Mechanisms and Mediators of the Skeletal Muscle Repeated Bout Effect

Effects of Eccentric Exercise of the Extensors on Eccentric Exercise-Induced Muscle Damage of the Flexors in Limbs

INTRODUCTION

We tested the hypothesis that muscle damage protection effect would be induced by its antagonist muscle eccentric exercise.

METHODS

Sedentary young (20-28 yr) men were randomly assigned into six groups; three groups each for arm or leg exercise group ( n = 12/group). One group performed two bouts of 30 maximal eccentric contractions (30MaxEC) of the elbow flexors (EF) or 60 maximal eccentric contractions (60MaxEC) of the knee flexors (KF) using a different arm (contra-EF-EF) or leg (contra-KF-KF) between bouts. The other two groups performed 30MaxEC of the elbow extensors (EE) or 60MaxEC of the knee extensors (KE) first followed by the 30MaxEC of EF or 60MaxEC of KF using the ipsilateral (ipsi-EE-EF, ipsi-KE-KF) or contralateral limb (contra-EE-EF, contra-KE-KF). The two exercise bouts were separated by 2 wk for all groups. Changes in muscle damage markers before to 5 d after exercise were compared among the groups by mixed-design two-way ANOVA.

RESULTS

Changes in the markers after the second bout of the ipsi-EE-EF, contra-EE-EF, ipsi-KE-KF, and contra-KE-KF groups were smaller ( P < 0.05) than those after the first bout of the contra-EF-EF and contra-KF-KF groups, respectively. The changes after the second bout were smaller ( P < 0.05) for the ipsi-EE-EF than contra-EE-EF, and ipsi-KE-KF than contra-KE-KF group; however, those in the contra-EE-EF and contra-KE-KF groups were larger ( P < 0.05) than those after the second bout of the contra-EF-EF and contra-KF-KF groups.

CONCLUSIONS

These results showed that the magnitude of muscle damage of EF or KF was reduced by the initial bout of EE or KE eccentric exercise performed by both ipsilateral and contralateral limbs, suggesting that muscle damage protective effect is conferred by the antagonist muscle in the same and opposite limbs.

Advancing Age Is Not Associated With Greater Exercise-Induced Muscle Damage: A Systematic Review, Meta-Analysis, and Meta-Regression

OBJECTIVE

The aim of this paper was to undertake a Preferred Reporting Items for Systematic Reviews and Meta-Analysis-accordant meta-analysis comparing exercise-induced muscle damage (EIMD) in older and younger adults.

METHODS

Google Scholar, PubMed, and SPORTDiscus were searched in June 2023 for the terms "ageing" OR "age" OR "middle-aged" OR "old" OR "older" OR "elderly" OR "masters" OR "veteran" AND "muscle damage" OR "exercise-induced muscle damage" OR "exercise-induced muscle injury" OR "contraction-induced injury" OR "muscle soreness" OR "delayed onset muscle soreness" OR "creatine kinase." From 1,092 originally identified titles, 36 studies were included which had an exercise component comparing a younger against an older group. The outcome variables of EIMD were muscle function, muscle soreness, and creatine kinase. A meta-analysis was conducted on change to EIMD after exercise in older versus younger adults using standardized mean difference (SMD) and an inverse-variance random effects model.

RESULTS

Change after 24 and 72 hr, and peak change, in muscle function was not different between old and young (SMD range = -0.16 to -0.35). Muscle soreness was greater in younger than older adults for all comparisons (SMD range = -0.34 to -0.62). Creatine kinase was greater in younger than older adults at 24 hr (SMD = -0.32), as was peak change (SMD = -0.32). A relationship between sex and peak muscle function change was evident for males (SMD = -0.45), but not females (SMD = -0.44). All other meta-regression was nonsignificant.

CONCLUSION

Advancing age is not associated with greater symptoms of EIMD. The implication of this study is that the older adults can pursue regular physical activity without concern for experiencing greater EIMD.

The reliability of functional and systemic markers of muscle damage in response to a flywheel squat protocol

PURPOSE

To characterize the magnitude, timescale, and reliability of changes in functional and systemic outcome markers following moderate (MIR) and high (HIR) isoinertial resistance flywheel squat protocols (FSP).

METHODS

Twenty-four resistance-trained males completed two exercise trials (ET1 & ET2) separated by 32 days. Functional and systemic markers were assessed at pre-exercise (PRE), immediately post-exercise (IP), and 24 (24H), 48 (48H), and 72 (72H) hours post-exercise. Three-way group x trial x time repeated measures ANOVAs were conducted to compare all dependent variables between groups (MIR & HIR) and experimental trials across time. Test-retest reliability between trials was assessed using intraclass correlation coefficients (ICC).

RESULTS

At IP, both groups exhibited significantly decreased active range of motion, perceived recovery status, squat maximal voluntary isometric contraction force, and vertical jump performance, along with significantly increased muscle thickness and echo intensity (ultrasound), muscle soreness, and creatine kinase when compared to PRE. Most outcomes remained perturbed at 24H and 48H, especially in the HIR group. By 72H, only a subset of variables remained significantly changed from PRE. No significant attenuation of outcomes between trials were observed and test-retest reliability between trials was excellent for the FSP and moderate to excellent for most outcomes in both groups.

CONCLUSION

Our findings indicate that the FSP is a robust and repeatable exercise stimulus capable of eliciting significant exercise-induced muscle damage and reliable subsequent perturbations to functional and systemic markers of muscle damage. Our findings also support the use of crossover designs in future EIMD research designs with resistance-trained men.

Cellular deconstruction of the human skeletal muscle microenvironment identifies an exercise-induced histaminergic crosstalk

Plasticity of skeletal muscle is induced by transcriptional and translational events in response to exercise, leading to multiple health and performance benefits. The skeletal muscle microenvironment harbors myofibers and mononuclear cells, but the rich cell diversity has been largely ignored in relation to exercise adaptations. Using our workflow of transcriptome profiling of individual myofibers, we observed that their exercise-induced transcriptional response was surprisingly modest compared with the bulk muscle tissue response. Through the integration of single-cell data, we identified a small mast cell population likely responsible for histamine secretion during exercise and for targeting myeloid and vascular cells rather than myofibers. We demonstrated through histamine H1 or H2 receptor blockade in humans that this paracrine histamine signaling cascade drives muscle glycogen resynthesis and coordinates the transcriptional exercise response. Altogether, our cellular deconstruction of the human skeletal muscle microenvironment uncovers a histamine-driven intercellular communication network steering muscle recovery and adaptation to exercise.

Neuromuscular electrical stimulation producing low evoked force elicits the repeated bout effect on muscle damage markers of the elbow flexors

This study examined the repeated bout effect (RBE) on muscle damage markers following two bouts of neuromuscular electrical stimulation (NMES) in untrained individuals. Following familiarization, participants received 45 consecutive NMES to the biceps brachii at an intensity that produced low evoked force for the elbow flexors. Muscle damage markers (maximal voluntary isometric contraction [MVIC], elbow range of motion [ROM], muscle soreness via visual analogue scale [VAS] scores, pressure pain threshold [PPT], and muscle thickness) were measured before (PRE), after (POST), 1 day after (24 POST), and 2 days after (48 POST) NMES. Following 1 week of rest, procedures were replicated. Separate repeated measures two-way ANOVAs examined each measure. There were no interactions or bout main effects for MVIC or ROM. Time main effects indicated PRE MVIC was greater than POST (p ​= ​0.002) and 24-POST (p ​= ​0.024), and PRE ROM was greater than POST (p ​= ​0.036). There was no interaction for muscle thickness. Respective time and bout main effects indicated muscle thickness at PRE was less than POST (p ​= ​0.017), and second-bout muscle thickness (p ​= ​0.050) was less compared to the initial-bout. For PPT, there was an interaction (p ​= ​0.019). Initial-bout PRE PPT was less than POST (p ​= ​0.033). Initial-bout 48-POST PPT was less than second-bout 48-POST (p ​= ​0.037). There was a significant interaction for VAS (p ​= ​0.009). Initial-bout PRE VAS was less than POST (p ​= ​0.033) and 24-POST (p ​= ​0.015). Initial-bout POST and 24-POST VAS were greater than second-bout POST (p ​= ​0.023) and 24-POST (p ​= ​0.006), respectively. The results support RBE on muscle damage markers related to inflammation, but not MVIC and ROM.

Muscle soreness but not neuromuscular fatigue responses following downhill running differ according to the number of exercise bouts

Repeated sessions of eccentric-biased exercise promote strength gains through neuromuscular adaptation. However, it remains unclear whether increasing the number of these sessions can mitigate the extent of neuromuscular fatigue and exercise-induced muscle damage (EIMD) in response to a standardised eccentric-biased bout. Twelve healthy untrained adults (five females and seven males; 25.1 ± 4.9 years; andV ˙ O 2 max $\dot{V}{\mathrm{O}}_{2\,\max }$ : 49.4 ± 6.2 mL kg-1 min-1) completed two blocks of five downhill running (DR) sessions on a motorised treadmill at a speed equivalent to 60%-65%V ˙ O 2 max $\dot{V}{\mathrm{O}}_{2\,\max }$ for 15-30 min. Knee extensor maximal voluntary isometric torque (MVT), electrically evoked measures of neuromuscular fatigue (peripheral and central components), and lower-limb perceived muscle soreness (PMS) and perceived load (RPE × session duration) were assessed before and immediately after a 15 min standardised DR bout at baseline and after 5 and 10 DR sessions. MVT decreased following a standardised DR bout (p < 0.01) similarly at all three time points (-14%, -11% and -9%; p > 0.05). The same observations were found for all peripheral and central neuromuscular fatigue indicators after 0, 5 and 10 DR sessions. Quadriceps (but not plantar flexor or gluteus) PMS was lower after 10 DR sessions (8.7 ± 8.5 mm) compared to baseline (29.6 ± 22.2 mm and p = 0.01), but no difference was observed after 5 DR sessions (15.4 ± 11.9 mm and p = 0.08). Ten repeated sessions of eccentric-biased exercise led to a reduction in quadriceps femoris PMS following a standardised DR bout but neither 5 nor 10 sessions altered the central or peripheral fatigue responses to the same standardised DR bout. These findings suggest distinct physiological adaptations to repeated eccentric-biased exercise regarding EIMD and neuromuscular fatigue.

Do Cheaters Prosper? Effect of Externally Supplied Momentum During Resistance Training on Measures of Upper Body Muscle Hypertrophy

Exercise technique, defined as the controlled execution of bodily movements to ensure an exercise effectively targets specific muscle groups while minimizing the risk of injury, is a resistance training (RT) variable frequently highlighted as critical to successful RT program outcomes, with proper technique suggested to play a role in maximizing muscle development. This study examined the effects of externally applied momentum on RT-induced muscular adaptations in the upper extremities. Thirty young adults were recruited to participate in a within-participant design, with one limb randomly allocated to perform biceps curls and triceps pushdowns using strict form (STRICT) and the other using external momentum (CHEAT). Participants completed four sets of each exercise with 8-12 repetitions until momentary muscular failure, twice a week for eight weeks. We obtained pre-post proximal and distal measures of muscle thickness for the elbow flexors and extensors, and assessed circumference changes in the upper arms. Data were analyzed in a Bayesian framework including both univariate and multivariate mixed effect models with random effects. Differences between conditions were estimated as average treatment effects, with inferences based on posterior distributions and Bayes Factors (BFs). Results showed similar between-conditions increases for all muscle thickness sites as well as circumference measures, generating consistent support for the null hypothesis (BF = 0.06 to 0.61). Volume load was markedly greater for CHEAT compared to STRICT across each week of the intervention. In conclusion, the use of external momentum during single-joint RT of the upper extremities neither helped nor hindered hypertrophy of the target muscles.

Effects of Vegan and Omnivore Diet on Post-Downhill Running Economy and Muscle Function

OBJECTIVES

The objective of this study was to examine the difference between the extent of muscle damaging exercise on muscle function variables of vegans and omnivores.

METHODS

Twenty recreationally trained participants completed the study. Participants were assigned to either vegan (n = 10) or omnivore (n = 10) groups. Subjects completed a consent visit followed by 2 visits consisting of running exercise sessions and test familiarization. They returned to the laboratory for visit 4 3-5 days after visit 3 to complete the testing battery. Following the testing, the participants performed a downhill run on the treadmill at -15% grade and approximately 70% of their speed at VO2peak and repeated the testing battery upon completion. Participants were asked to track their food intake. Visits 5, 6, and 7 took place 24, 48, and 72 h following the downhill running protocol, respectively, and consisted of the same testing battery used during visit 4. The detection of differences was performed using two-way (group x time) mixed factorial ANOVA with repeated measures.

RESULTS

No group x time interactions were noted for running economy or any of the dependent variables. Main effects of time were found for muscle thickness (p<.001) with small effect sizes (d=-0.194 to d=-0.265), pain pressure threshold (p=.002) with medium effect sizes (d=.460 to d=.461), NPRS scale (p<.001) with large effect sizes (d = -0.776 to d=-1.520), and jump height (p<.002) with small to medium effect sizes (d=.304 to d=.438). Nutritional analysis compared the two groups revealed no difference (p>.05) between relative intake of macronutrients and that both exceeded typical recommendations for protein (vegan group - 1.4 g/kg, omnivore group - 1.6 g/kg).

CONCLUSION

The lack of differences in recovery between the groups suggests that nutritional adequacy may play a role in recovery. Recovery from downhill running might be influenced by several factors beyond diet, such as exercise protocol intensity, individual fitness levels, and age.

Arterial and Venous Pressure Dynamics in Blood Flow Restriction Versus Traditional Strength Training

Strength training responses are influenced by sets, repetitions, and mechanical load, whereas Blood Flow Restriction (BFR) training adds the variable of temporarily restricting blood flow via a tourniquet. This has intensified scientific discussions regarding the vascular responses and thereby safety of the BFR method. To address these concerns, we investigated intravascular pressure changes during low-load (LL-RT), low-load with BFR (LL-BFR-RT), and high-load (HL-RT) exercise. Ten healthy men (26.8 ± 4.59 years) performed unilateral biceps curls to failure in a randomized cross-over design: (1) LL-RT (30% 1RM), (2) LL-BFR-RT (30% 1RM, 50% LOP), and (3) HL-RT (75% 1RM). Total workload was significantly higher in LL-RT (692 ± 251 kg) compared to LL-BFR-RT (378 ± 58.7 kg) and HL-RT (327 ± 65.1 kg, p < 0.001). In terms of mean values, LL-BFR-RT resulted in higher diastolic and mean arterial pressures during rest periods between sets compared to other conditions (p ≤ 0.02). Both LL-RT and LL-BFR-RT led to longer durations spent at increased diastolic (above 90 mmHg, LL-RT: ~419 s vs. LL-BFR-RT: ~356 s vs. Hl-RT: ~122 s), systolic (above 140 mmHg, LL-RT: ~437 s vs. LL-BFR-RT: ~336 s vs. HL-RT: ~199 s), and mean arterial pressures (above 107 mmHg, LL-RT: ~451 s vs. LL-BFR-RT: ~384 s vs. HL-RT: ~168 s) compared to HL-RT (p ≤ 0.028). Relative to total exercise time, LL-BFR-RT resulted in higher proportion of time spent at elevated diastolic (above 90 mmHg, LL-RT: ~56.5% vs. LL-BFR-RT: ~68.7% vs. Hl-RT: ~33.5%) and mean arterial pressures (above 107 mmHg, LL-RT: ~60.8% vs. LL-BFR-RT: ~74.0% vs. HL-RT: ~45.7%) compared to HL-RT (p ≤ 0.034). Peripheral venous pressure was significantly higher in LL-BFR-RT compared to other conditions (p < 0.001), with both absolute and relative time spent at higher pressures (above 75 mmHg, LL-RT: ~57.0 s and ~ 9.12% vs. LL-BFR-RT: ~424 s and ~ 81.7% vs. HL-RT: ~36.0 s and ~ 8.99%, p ≤ 0.002). Our results suggest that BFR training performed to failure imposes greater arterial and venous stress in the exercising limb compared to high-load training without BFR, particularly due to prolonged exposure to elevated pressures. Further research is needed to assess the potential risks of elevated local arterial and venous pressure responses by frequent BFR use, particularly in populations with pre-existing medical conditions.

Recycle, repair, recover: the role of autophagy in modulating skeletal muscle repair and post-exercise recovery

Skeletal muscle is a highly plastic tissue that can adapt relatively rapidly to a range of stimuli. In response to novel mechanical loading, e.g. unaccustomed resistance exercise, myofibers are disrupted and undergo a period of ultrastructural remodeling to regain full physiological function, normally within 7 days. The mechanisms that underpin this remodeling are believed to be a combination of cellular processes including ubiquitin-proteasome/calpain-mediated degradation, immune cell infiltration, and satellite cell proliferation/differentiation. A relatively understudied system that has the potential to be a significant contributing mechanism to repair and recovery is the autophagolysosomal system, an intracellular process that degrades damaged and redundant cellular components to provide constituent metabolites for the resynthesis of new organelles and cellular structures. This review summarizes our current understanding of the autophagolysosomal system in the context of skeletal muscle repair and recovery. In addition, we also provide hypothetical models of how this system may interact with other processes involved in skeletal muscle remodeling and provide avenues for future research to improve our understanding of autophagy in human skeletal muscle.

The Effects of Near-Infrared Phototherapy Preirradiation on Lower-Limb Muscle Strength and Injury After Exercise: A Systematic Review and Meta-analysis

OBJECTIVE

To assess near-infrared preirradiation effects on postexercise lower-limb muscle damage and function and determine optimal dosage.

DATA SOURCES

PubMed, Embase, Cochrane Library, EBSCO, Web of Science, China National Knowledge Infrastructure, and Wanfang Data were systematically searched (2009-2023).

STUDY SELECTION

Randomized controlled trials of near-infrared preirradiation on lower-limb muscles after fatigue exercise were incorporated into the meta-analysis. Out of 4550 articles screened, 21 met inclusion criteria.

DATA EXTRACTION

The included studies' characteristics were independently extracted by 2 authors, with discrepancies resolved through discussion or by a third author. Quality assessment was performed using the Cochrane risk of bias tool and the Grading of Recommendations, Assessment, Development, and Evaluation System.

DATA SYNTHESIS

In 21 studies, near-infrared preirradiation on lower-limb muscles inhibited the decline in peak torque (standardized mean difference [SMD], 1.33; 95% confidence interval [CI], 1.08-1.59; p<.001; increasing 27.97±4.87N·m), reduced blood lactate (SMD, -0.2; 95% CI, -0.37 to -0.03; p=.272; decreasing 0.54±0.42mmol/L), decreased creatine kinase (SMD, -2.11; 95% CI, -2.57 to -1.65; p<.001; decreasing 160.07±27.96U/L), and reduced delayed-onset muscle soreness (SMD, -0.53; 95% CI, -0.81 to 0.24; p<.001). Using a 24-hour cutoff revealed 2 trends: treatment effectiveness depended on power and energy density, with optimal effects at 24.16 J/cm2 and 275 J/cm2 for energy, and 36.81 mW/cm2 and 5495 mW/cm2 for power. Noting that out of 21 studies, 19 are from Brazil, 1 from the United States, and 1 from Australia, and the results exhibit high heterogeneity.

CONCLUSIONS

Although we would have preferred a more geographic dispersion of laboratories, our findings indicate that near-infrared preirradiation mitigates peak torque decline in lower-limb muscles. Influenced by energy and power density with a 24-hour threshold, optimal energy and power densities are observed at 24.16 J/cm2, 275 J/cm2, 36.81 mW/cm2, and 5495 mW/cm2, respectively. Laser preirradiation also reduces blood lactate, creatine kinase, and delayed-onset muscle soreness.

No effect of grape juice on exercise-induced muscle damage or performance in male runners: a randomized, placebo-controlled, triple-blind clinical trial

This study aimed to verify the effect of grape juice (Vitis Labrusca) intake on exercise-induced muscle damage (EIMD) and exercise performance parameters (5 km running time-trial (TT), running economy, and countermovement jump (CMJ)). Twenty trained male runners were randomized into two blinded groups and consumed either placebo (n = 9) or grape juice (n = 11) for six consecutive days (600 mL/day). On the fourth day, the participants performed a downhill running (-15%) at speed that elicited 70% V̇O2max for 20 min, to induce muscle damage, followed by assessment of running economy, 5 km TT, and CMJ tests. Blood samples were obtained before and after the exercise tests for quantifying total phenols, creatine kinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH). On the sixth day, blood parameters and CMJ were evaluated. A two-way Analysis of covariance (ANCOVA) mixed model was employed for data analysis, the effects were the juice groups, measurement and a interaction between the factors. EIMD was confirmed by increased levels of indirect markers (serum AST and LDH activities) and an impairment in TT and CMJ performances after 48 h. The 5 km TT, economy, and CMJ were compromised after EIMD, to a similar extent in the groups. Blood concentrations of CK, LDH, AST, and total phenolic compounds presented similar time course behavior between the groups, showing no group × time interaction effects. In conclusion, grape juice consumption over 6 days did not attenuate EIMD markers or the impairment in running performance in trained male runners. (ReBEC number: RBR-9jkkvbb).

Bridging the Gap Between Training and Competition in Elite Rink Hockey: A Pilot Study

BACKGROUND

Monitoring training load and competition load is crucial for evaluating and improving athlete performance. This study proposes an applied approach to characterize and classify the training task specificity in relation to competition in a top-level rink hockey team, considering external and internal load from training tasks and competition.

HYPOTHESIS

Training tasks and game demands have significant dose-response differences, and exercises can be classified successfully based on their physiological and biomechanical demands.

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

Level 5.

METHODS

Ten elite-level male rink hockey players participated in this study. Players were monitored on 6 different task categories during 8 training sessions and 2 official games. A linear mixed model with random intercepts was used to compare training tasks and competition load, accounting for individual repeated measures. A 2-step cluster analysis was performed to classify the training tasks and games based on physiological and biomechanical load, employing log-likelihood as the distance measure and Schwartz's Bayesian criterion.

RESULTS

Average heartrate, maximum heartrate, and high-speed skating (18.1-30 km/h) were the best physiological load predictors, while the most effective biomechanical load predictors were impacts [8-10] g(n), decelerations [-10 to -3]m/s²(n), and accelerations [3-10]m/s²(n). Different physiological and biomechanical responses were verified between training tasks and match demands. A 4-quadrant efforts assessment for each task category revealed that training tasks used by the team in the analysis presented lower biomechanical and physiological load demands than competition.

CONCLUSION

Training tasks failed to adequately replicate the specific demands of competition, especially regarding high mechanical stress, such as the absence of high-intensity impacts and decelerations.

CLINICAL RELEVANCE

This method of classification of training tasks may allow coaches to understand further the specificity and contribution of each task to competition demands, consequently improving the capacity of load management and the preparedness and readiness of players for competition.

Comparing the Effects of Collagen Hydrolysate and Dairy Protein on Recovery from Eccentric Exercise: A Double Blind, Placebo-Controlled Study

BACKGROUND

Consuming collagen hydrolysate (CH) may improve symptoms of exercise-induced muscle damage (EIMD); however, its acute effects have not been compared to dairy protein (DP), the most commonly consumed form of protein supplement. Therefore, this study compared the effects of CH and DP on recovery from EIMD.

METHODS

Thirty-three males consumed either CH (n = 11) or DP (n = 11), containing 25 g of protein, or an isoenergetic placebo (n = 11) immediately post-exercise and once daily for three days. Indices of EIMD were measured before and 30 min and 24, 48, and 72 h after 30 min of downhill running on a -15% slope at 80% of VO2max speed.

RESULTS

Downhill running induced significant EIMD, with time effects (all p < 0.001) for the delayed onset of muscle soreness (visual analogue scale), countermovement jump height, isometric midthigh pull force, maximal voluntary isometric contraction force, running economy, and biomarkers of muscle damage (creatine kinase) and inflammation (interleukin-6, high-sensitivity C-reactive protein). However, no group or interaction effects (all p > 0.05) were observed for any of the outcome measures.

CONCLUSIONS

These findings suggest that the post-exercise consumption of CH or DP does not improve indices of EIMD during the acute recovery period in recreationally active males.

Acute effects of intra-training carbohydrate ingestion in CrossFit® trained adults: a randomized, triple-blind, placebo-controlled crossover trial

Carbohydrate (CHO) intake during exercise could decrease the subjective perceived exertion and promote recovery; however, the effects of intra-training CHO ingestion remain uncertain in CrossFit® (CF) sessions. Therefore, the aim of this randomized, triple-blind, placebo-controlled crossover trial was to investigate the effect of acute CHO intake during a CF session on the delayed onset muscle soreness (DOMS), the perceived exertion (RPE), performance, recovery, and metabolic markers (capillary lactate and glucose) in CF athletes. Twenty-three male athletes trained in CF ingested CHO (60 g of maltodextrin + fructose) or a placebo (PLA) during a CF session. DOMS was assessed 24 and 48 h after the CF session. The Counter Movement Jump (CMJ) test and the Deep Squat test at 70% of the athlete's body weight (AST70) were performed before, immediately after, and 24 h after the session. Perceived exertion, Feeling Scale (FS), Gastrointestinal Distress Score (GDS), heart rate, capillary lactate, and glucose were assessed across the session. CHO supplementation did not improve DOMS (all P ≥ 0.127), CMJ, or AST70 parameters (all P ≥ 0.053) compared to PLA. There were no differences between CHO and PLA in RPE, FS, GDS, heart rate (all P ≥ 0.088), performance (e.g., nº of repetitions; all P ≥ 0.556), or lactate levels (P = 0.810). However, glucose levels increased from the back squat to the WOD and remained stable after the AMRAP (P < 0.001). In conclusion, acute CHO intake during a CF session did not improve DOMS, perceived exertion, performance, recovery, or metabolic markers in CF athletes. TRN: NCT06440343. Date: 2024-05-10.

Does the Repeated-Bout Effect Influence Post-Activation Performance Enhancement in Recreational Runners?

Purpose: This study examined how a low dose of an eccentric-oriented lunge exercise could induce the repeated-bout effect (RBE) and affect the subsequent post-activation performance enhancement (PAPE) in recreational runners. Methods: Twenty male recreational runners (32.1 ± 2.8 years; 173.4 ± 6.1 cm; 73.3 ± 11.5 kg; 57.8 ± 7.2 mL·kg-1·min-1) were divided into control (N = 10) and experimental (N = 10) groups. In the first and fourth weeks, the groups were assessed for jump capacity, dynamic balance, and submaximal running kinematics before and after an incremental shuttle-run test until exhaustion. The experimental group was also submitted to two sessions of the eccentric-oriented lunge exercise (3 sets of 10 repetitions with 2 min of passive recovery) in the second and third weeks. Results: We observed that the first session promoted muscle damage, which was significantly (p < .05) reduced after the second training session, thus indicating an RBE. Meanwhile, there was no effect of the RBE on dynamic balance and submaximal running kinematics in the post-intervention. However, there was a significant increase in countermovement jump height (p = .008) for the experimental group when compared to the control group, although no PAPE was observed. Conclusions: The current results demonstrate that a simple, low-dose eccentric-oriented exercise may induce an RBE, leading to reduced muscle damage and a possibly improved lower limbs' muscle power in recreational runners. However, the absence of PAPE effects suggests that the RBE may not directly influence the potentiation/fatigue balance after fatiguing running exercises.

The influence of muscle strength and aerobic fitness on functional recovery in elite female soccer players

BACKGROUND

We examined the influence of muscle strength and aerobic fitness on wellbeing and muscle function recovery in female soccer players.

METHODS

Sixteen players from the English Women's Super League (age: 26±4 yrs; height, 1.70±0.07 m; mass, 67.9±6.4 kg) completed an isometric mid-thigh pull test (IMTP) and maximal aerobic speed test (MAST). Using a median split, players were divided by strength into high (H-IMTP) and low (L-IMPT) groups and by fitness into high (H-MAST) and low (L-MAST) groups. Countermovement jump height (CMJ), Reactive Strength Index (RSI) and wellbeing were measured 2 days prematch, then 3 subsequent days post-match (M+1, M+2, M+3).

RESULTS

In H-IMTP, CMJ, RSI and wellbeing were higher at M+1-M+3 (P<0.05). At M+3, CMJ in H-IMTP was 30.3±3.5 cm vs. 26.2±3.4 in L-IMTP. CMJ and wellbeing were unaffected by fitness, but RSI was lower at M+1-M+3 in the L-IMTP group (P<0.05).

CONCLUSIONS

In conclusion, isometrically stronger but not aerobically fitter female soccer players recover quicker after matches.

The repeated bout effect evokes the training-induced skeletal muscle cellular memory

Physical exercise is well-established as beneficial for health. With the 20th-century epidemiological transition, promoting healthy habits like exercise has become crucial for preventing chronic diseases. Stress can yield adaptive long-term benefits, potentially transmitted trans-generationally. Physical training exposes individuals to metabolic, thermal, mechanical, and oxidative stressors, activating cell signaling pathways that regulate gene expression and adaptive responses, thereby enhancing stress tolerance - a phenomenon known as hormesis. Muscle memory is the capacity of skeletal muscle to respond differently to environmental stimuli in an adaptive (positive) or maladaptive (negative) manner if the stimuli have been encountered previously. The Repeated Bout Effect encompasses our skeletal muscle capacity to activate an intrinsic protective mechanism that reacts to eccentric exercise-induced damage by activating an adaptive response that resists subsequent damage stimuli. Deciphering the molecular mechanism of this phenomenon would allow the incorporation of muscle memory in training programs for professional athletes, active individuals looking for the health benefits of exercise training, and patients with "exercise intolerance." Moreover, enhancing the adaptive response of muscle memory could promote healing in individuals who traditionally do not recover after immobilization. The improvement could be part of an exercise program but could also be targeted pharmacologically. This review explores Repeated Bout Effect mechanisms: neural adaptations, tendon and muscle fiber property changes, extracellular matrix remodeling, and improved inflammatory responses.

Changes in motor unit behaviour across repeated bouts of eccentric exercise

Unaccustomed eccentric exercise (EE) is protective against muscle damage following a subsequent bout of similar exercise. One hypothesis suggests the existence of an alteration in motor unit (MU) behaviour during the second bout, which might contribute to the adaptive response. Accordingly, the present study investigated MU changes during repeated bouts of EE. During two bouts of exercise where maximal lengthening dorsiflexion (10 repetitions × 10 sets) was performed 3 weeks apart, maximal voluntary isometric torque (MVIC) and MU behaviour (quantified using high-density electromyography; HDsEMG) were measured at baseline, during (after set 5), and post-EE. The HDsEMG signals were decomposed into individual MU discharge timings, and a subset were tracked across each time point. MVIC was reduced similarly in both bouts post-EE (Δ27 vs. 23%, P = 0.144), with a comparable amount of total work performed (∼1,300 J; P = 0.905). In total, 1,754 MUs were identified and the decline in MVIC was accompanied by a stepwise increase in discharge rate (∼13%; P < 0.001). A decrease in relative recruitment was found immediately after EE in Bout 1 versus baseline (∼16%; P < 0.01), along with reductions in derecruitment thresholds immediately after EE in Bout 2. The coefficient of variation of inter-spike intervals was lower in Bout 2 (∼15%; P < 0.001). Our data provide new information regarding a change in MU behaviour during the performance of a repeated bout of EE. Importantly, such changes in MU behaviour might contribute, at least in part, to the repeated bout phenomenon.

Effect of a honey-sweetened beverage on muscle soreness and recovery of performance after exercise-induced muscle damage in strength-trained females

Background

This study explores a novel approach to mitigating delayed-onset muscle soreness (DOMS), a common issue among strength-trained females. By investigating the potential of a honey-sweetened beverage, which contains anti-inflammatory properties, we aim to enhance muscle recovery after exercise-induced muscle damage (EIMD).

Method

A randomized, cross-over, placebo-controlled, and double-blinded study was conducted with sixteen female strength athletes. Firstly, the baseline measurements were recorded, and participants were randomly divided into two conditions: honey-sweetened beverage (HSB; 70 g of honey in 250 mL water with a concentration of 28%) and placebo (PLA; 250 mL of water with 70 g of artificial sweetener). The HSB and PLA were consumed 90 min before the EIMD started (200 vertical jumps with 10% body-weighted vests). Recovery monitoring of performance indicators and DOMS was performed after EIMD. The results of wall-sit, V-Sit and reach flexibility test (VSFT), vertical jump height (VJH), pressure pain threshold (PPT), and one repetition maximum (IRM) tests were recorded 48 h after EIMD. Also, DOMS was recorded using the visual analog scale (VAS) before the start of the test and immediately, 12, 24, and 48 h after EIMD. A one-week interval was considered a washout period for each condition. The collected data were analyzed by repeated measures of ANOVA and Bonferroni post hoc test and dependent t-test at P ≤ 0.05 level.

Results

Compared to PLA, HSB ingestion improves wall-sit performance (p = 0.003), 1RM (p = 0.019), and RPE (p = 0.003) after EIMD. However, no significant differences were observed between BL, PLA, and HSB in VJH (p = 0.384), VSFT (p = 0.840), and PPT (p = 0.151) after EIMD. Furthermore, HSB, compared to PLA, considerably decreased the values of DOMS immediately, 12, 24, and 48 h after EIMD (p < 0.05).

Conclusion

Our findings illustrated that ingesting HSB in strength-trained females can be a helpful strategy for improving recovery indicators such as muscle strength, endurance, and muscle soreness after EIMD.

Comparison of Metabolic, Ionic, and Electrolyte Responses to Exhaustive Low-Load Strength Training With and Without Blood Flow Restriction and High-Load Resistance Training

Low-load blood-flow-restriction resistance training (LL-BFR-RT) is gaining popularity, but its physiological effects remain unclear. This study aimed to compare LL-BFR-RT with low-load resistance exercise (LL-RT) and high-load resistance exercise (HL-RT) on metabolism, electrolytes, and ions in the lower extremities by invasive catheter measurements, which are crucial for risk assessment. Ten healthy men (27.6 ± 6.4 years) completed three trials of knee-extensor exercises with LL-RT (30% 1RM), LL-BFR-RT (30% 1RM, 50% limb occlusion pressure), and HL-RT (75% 1RM). The exercise protocol consisted of four sets to voluntary muscle failure with 1 min of rest between sets. Blood gas analysis was collected before, during, and after each trial through intravenous catheters at the exercising leg. LL-BFR-RT had lower total workload (1274 ± 237 kg, mean ± SD) compared to LL-RT (1745 ± 604 kg), and HL-RT (1847 ± 367 kg, p < 0.01), with no difference between LL-RT and HL-RT. Pain perception did not differ significantly. Exercise-induced drop in oxygen partial pressure, lactate accumulation and electrolyte shifts (with increased [K+]) occurred during under all conditions (p < 0.001). Creatine kinase and lactate dehydrogenase increased significantly 24- and 48-h postexercise under all three conditions (p < 0.001). This study, using invasive catheter measurements, found no significant differences in metabolic, ionic, and electrolyte responses among LL-BFR-RT, LL-RT, and HL-RT when exercised to voluntary muscular failure. LL-BFR-RT reduced time to failure without specific physiological responses.

Match-related fatigue in basketball: A systematic review

This study aimed to systematically review fatigue responses following basketball match-play and during congested match schedules, considering performance, physiological, athlete-reported, and sleep-related outcomes. Relevant articles published until 23 January 2024 were searched using Scopus, Web of Science, and SPORTDiscus. After screening, 44 studies were included in the systematic review. The main findings indicate that, in most cases, vertical jumping and linear sprinting showed significant decrements at match-end (<1 hour post-match) compared to pre-match [small-to-very large effect sizes (ES)], with persistent (≥1 hour post-match) impairments lasting 24-48 hours in jumping (only in males, small-to-very large ES) and linear sprinting (moderate-to-very large ES). Physiological changes generally included significant increases (moderate-to-very large ES) in cortisol and nutrient metabolism markers at match-end, alongside persistent increases in muscle damage (mainly at 13-72 hours post-match) and inflammation (13-48 hours). Finally, match-play generally increased muscle soreness (mainly at 24-48 hours, moderate-to-very large ES) and perceived fatigue (mainly at match-end), with unclear effects on mood, and no apparent impact on sleep-related outcomes. Research assessing congested match schedules is limited, although possible worsening in muscle damage, inflammation, perceived fatigue and well-being were observed in male players. Overall, these findings indicate an impairment in some of the reviewed performance, physiological, and athlete-reported outcomes.

Exploring the Dose-Response Relationship Between Estimated Resistance Training Proximity to Failure, Strength Gain, and Muscle Hypertrophy: A Series of Meta-Regressions

BACKGROUND

The proximity to failure in which sets are terminated has gained attention in the scientific literature as a potentially key resistance training variable. Multiple meta-analyses have directly (i.e., failure versus not to failure) or indirectly (e.g., velocity loss, alternative set structures) evaluated the effect of proximity to failure on strength and muscle hypertrophy outcomes categorically; however, the dose-response effects of proximity to failure have not been analyzed collectively in a continuous manner.

OBJECTIVE

To meta-analyze the aforementioned areas of relevant research, proximity to failure was quantified as the number of repetitions in reserve (RIR). Importantly, the RIR associated with each effect in the analysis was estimated on the basis of the available descriptions of the training interventions in each study. Data were extracted and a series of exploratory multilevel meta-regressions were performed for outcomes related to both strength and muscle hypertrophy. A range of sensitivity analyses were also performed. All models were adjusted for the effects of load, method of volume equating, duration of intervention, and training status.

RESULTS

The best fit models for both strength and muscle hypertrophy outcomes demonstrated modest quality of overall fit. In all of the best-fit models for strength, the confidence intervals of the marginal slopes for estimated RIR contained a null point estimate, indicating a negligible relationship with strength gains. However, in all of the best-fit models for muscle hypertrophy, the marginal slopes for estimated RIR were negative and their confidence intervals did not contain a null point estimate, indicating that changes in muscle size increased as sets were terminated closer to failure.

CONCLUSIONS

The dose-response relationship between proximity to failure and strength gain appears to differ from the relationship with muscle hypertrophy, with only the latter being meaningfully influenced by RIR. Strength gains were similar across a wide range of RIR, while muscle hypertrophy improves as sets are terminated closer to failure. Considering the RIR estimation procedures used, however, the exact relationship between RIR and muscle hypertrophy and strength remains unclear. Researchers and practitioners should be aware that optimal proximity to failure may differ between strength and muscle hypertrophy outcomes, but caution is warranted when interpreting the present analysis due to its exploratory nature. Future studies deliberately designed to explore the continuous nature of the dose-response effects of proximity to failure in large samples should be considered.

Aerobic Exercise Protects against Cardiotoxin-Induced Skeletal Muscle Injury in a DDAH1-Dependent Manner

Dimethylarginine dimethylaminohydrolase 1 (DDAH1) is a critical enzyme that regulates nitric oxide (NO) signaling through the degradation of asymmetric dimethylarginine (ADMA). Previous studies have revealed a link between the beneficial effects of aerobic exercise and the upregulation of DDAH1 in bones and hearts. We previously reported that skeletal muscle DDAH1 plays a protective role in cardiotoxin (CTX)-induced skeletal muscle injury and regeneration. To determine the effects of aerobic exercise on CTX-induced skeletal muscle injury and the role of DDAH1 in this process, wild-type (WT) mice and skeletal muscle-specific Ddah1-knockout (Ddah1MKO) mice were subjected to swimming training for 8 weeks and then injected with CTX. In WT mice, swimming training for 8 weeks significantly promoted skeletal muscle regeneration and attenuated inflammation, oxidative stress, and apoptosis in the gastrocnemius (GA) muscle after CTX injection. These phenomena were associated with increases in the protein expression of PAX7, myogenin, MEF2A, eNOS, SOD2, and peroxiredoxin 5 and decreases in iNOS expression in GA muscles. Swimming training also decreased serum ADMA levels and increased serum nitrate/nitrite (NOx) levels and skeletal muscle DDAH1 expression. Interestingly, swimming training in Ddah1MKO mice had no obvious effect on CTX-induced skeletal muscle injury or regeneration and did not repress the CTX-induced inflammatory response, superoxide generation, or apoptosis. In summary, our data suggest that DDAH1 is important for the protective effect of aerobic exercise on skeletal muscle injury and regeneration.

Impact of Eccentric Exercise Interventions with Small and Large Ranges of Motion on Rat Skeletal Muscle Tissue and Muscle Force Production

Eccentric training induces greater hypertrophy while causing more muscle damage than concentric training. This study examined the effects of small-range eccentric contractions (SR-ECCs) and large-range eccentric contractions (LR-ECCs) on muscle morphology, contractility, and damage in rats. Thirty male Fischer 344 rats were divided into five groups: small-range ECC single-bout (SR-ECCSB, n = 4), large-range ECC single-bout (LR-ECCSB, n = 4), SR-ECC intervention (SR-ECCIntv, n = 7), LR-ECC intervention (LR-ECCIntv, n = 8), and control (Cont, n = 7). These groups underwent transcutaneous electrical stimulation involving 80 ECCs twice a week for four weeks. The results indicated that the LR-ECCSB group had more Evans blue dye-positive fibers than other groups. The SR-ECCIntv group showed no increase in the mean myofiber cross-sectional area. However, Pax7+ and Ki67+ cells significantly increased in both ECCIntv groups compared to the Cont group, and the connective tissue area was significantly greater in the LR-ECCIntv than in others. Muscle force was lower in both ECCIntv groups compared to the Cont group. These findings suggest that SR-ECC intervention may induce a smaller increase in the number of fibers with a large myofiber cross-sectional area and satellite cell proliferation with less muscle damage and myofibrosis compared to LR-ECCs.

Youths Are Less Susceptible to Exercise-Induced Muscle Damage Than Adults: A Systematic Review With Meta-Analysis

PURPOSE

This meta-analysis aimed to (1) provide a comparison of peak changes in indirect markers of exercise-induced muscle damage (EIMD) in youths versus adults and (2) determine if the involved limb moderated this effect.

METHOD

Studies were eligible for inclusion if they (1) provided a human youth versus adult comparison; (2) provided data on muscle strength, soreness, or creatine kinase markers beyond ≥24 hours; and (3) did not provide a recovery treatment. Effect sizes (ES) were presented alongside 95% confidence intervals.

RESULTS

EIMD exhibited larger effects on adults than in youths for muscle strength (ES = -2.01; P < .001), muscle soreness (ES = -1.52; P < .001), and creatine kinase (ES = -1.98; P < .001). The random effects meta-regression indicated that the effects of upper- and lower-limb exercise in youths and adults were significant for muscle soreness (coefficient estimate = 1.11; P < .001) but not for muscle strength or creatine kinase (P > .05). As such, the between-group effects for muscle soreness (ES = -2.10 vs -1.03; P < .05) were greater in the upper than lower limbs.

CONCLUSION

The magnitude of EIMD in youths is substantially less than in their adult counterparts, and this effect is greater in upper than lower limbs for muscle soreness. These findings help guide practitioners who may be concerned about the potential impact of EIMD when training youth athletes.

Recovery from sport-induced muscle damage in relation to match-intervals in major events

Muscle damage could affect the next match performance in sports when the time to recover from a previous match is shorter. We examined the interval between matches in nine team sports (e.g., soccer, rugby, field hockey, basketball, volleyball, baseball) and two racket sports (badminton, tennis) in World Cups held in 2022-2023, 2020 Tokyo Olympic Games and Gland Slam in 2023. We then performed narrative review using three electronic databases (PubMed, Scopus, Google Scholar) to get information about muscle damage and recovery in the 11 sports, and discussed whether the intervals in the events would be enough for athletes. We found that the match intervals varied among sports and events ranging from 0 to 17 days. The interval was the shortest for softball (0-2 days) and the longest (5-17 days) for rugby. Regarding muscle damage, changes in muscle function and/or performance measures after a match were not reported for cricket, volleyball and softball, but some information was available for other sports, although the studies did not necessarily use athletes who participated in the major events. It was found that recovery was longer for soccer and rugby than other sports. Importantly, the match-intervals in the events did not appear to accommodate the recovery time required from the previous match in many sports. This could increase a risk of injury and affect players' conditions and health. Changing the match-intervals may be difficult, since it affects the budget of sporting events, but an adequate interval between matches should be considered for each sport from the player's and coach's point of view.

Pre-exercise cryotherapy reduces myoglobin and creatine kinase levels after eccentric muscle stress in young women

Introduction: The aim of this study was to investigate the effect of pre-exercise whole-body cryotherapy (WBC) on muscle damage indicators following eccentric treadmill exercise in young women. Methods: Twenty-seven participants underwent two 1-h downhill treadmill runs, replicating 60% of their maximal oxygen uptake, with a 4-week intermission for recovery and treatment application. In this intermission, one group underwent 20 sessions of WBC, delivered five times a week at -120°C for 3 min each, while the comparison group received no such treatment. Markers of muscle injury-serum myoglobin concentration, creatine kinase and lactate dehydrogenase activity and also uric acid, and cell-free DNA concentration-were measured before and after downhill runs. Results: The study observed a notable reduction in post-exercise myoglobin and CK levels in the WBC group after the second running session. Discussion: The results suggest that WBC can have a protective effects against muscle damage resulting from eccentric exercise.

Repeated Bout Effect of Downhill Running on Physiological Markers of Effort and Post Exercise Perception of Soreness in Trained Female Distance Runners

This study examined the effect of repeated bouts of level and downhill running on physiological markers of effort and exercise-induced muscle soreness in trained female distance runners. Ten participants (Age: 24.4 ± 2.0 years; V̇O2peak: 52.9 ± 1.1 mL·kg-1·min-1), naïve to downhill running, completed six alternate 5 min trials of level and downhill running (-15%) at a 70% velocity at V̇O2peak on two occasions, three weeks apart. Perceived muscle soreness was measured upon completion and in the 72 h post exercise. V̇O2, Heart Rate (HR), Blood Lactate (BLa), and Respiratory Exchange Ratio (RER) were lower running downhill (p < 0.016, ηp2 > 0.541). For the first downhill run, Rating of Perceived Exertion (RPE) was higher compared to that for level running (p = 0.051; d = 0.447), but for the remaining trials, RPE was lower when running downhill (p < 0.004; d > 0.745). V̇O2, HR, and RER were not different in the second bout (p > 0.070, ηp2 < 0.318); however, V̇O2 was lower in each downhill trial (Δ = 1.6-2.2 mL·kg-1·min-1; d = 0.382-0.426). In the second bout, BLa was lower (p = 0.005, ηp2 = 0.602), RPE in the first trial was lower (p = 0.002; d = 0.923), and post exercise perceived soreness of the gastrocnemius, quadriceps, and hamstrings was attenuated (p < 0.002; ηp2 > 0.693). Perceived soreness of the gluteal muscles was lower in the second bout immediately post exercise, 24 h, and 48 h post exercise (p < 0.025; d > 0.922). A repeated bout of downhill running attenuated perceived muscle soreness and may modulate the physiological and perceived physical demand of a second bout of level and downhill running.

Force-Time Characteristics of Repeated Bouts of Depth Jumps and the Effects of Compression Garments

No studies have reported ground reaction force (GRF) profiles of the repeated depth jump (DJ) protocols commonly used to study exercise-induced muscle damage. Furthermore, while compression garments (CG) may accelerate recovery from exercise-induced muscle damage, any effects on the repeated bout effect are unknown. Therefore, we investigated the GRF profiles of 2 repeated bouts of damage-inducing DJs and the effects of wearing CG for recovery. Nonresistance-trained males randomly received CG (n = 9) or placebo (n = 8) for 72 hours recovery, following 20 × 20 m sprints and 10 × 10 DJs from 0.6 m. Exercise was repeated after 14 days. Using a 3-way (set × bout × group) design, changes in GRF were assessed with analysis of variance and statistical parametric mapping. Jump height, reactive strength, peak, and mean propulsive forces declined between sets (P < .001). Vertical stiffness, contact time, force at zero velocity, and propulsive duration increased (P < .05). According to statistical parametric mapping, braking (17%-25% of the movement) and propulsive forces (58%-81%) declined (P < .05). During the repeated bout, peak propulsive force and duration increased (P < .05), while mean propulsive force (P < .05) and GRF from 59% to 73% declined (P < .001). A repeated bout of DJs differed in propulsive GRF, without changes to the eccentric phase, or effects from CG.

Effect of Spirulina Nigrita® Supplementation on Indices of Exercise-Induced Muscle Damage after Eccentric Protocol of Upper Limbs in Apparently Healthy Volunteers

Spirulina is a supplement with antioxidant and anti-inflammatory properties that may enhance performance and recovery after intense exercise. The present study aimed to investigate the effects of Spirulina Nigrita® on physical performance, and recovery markers after intense eccentric exercise in healthy moderately physically active volunteers. In a double-blind crossover design, participants were supplemented either with spirulina (42 mg Kg-1 BW per day) or a placebo for 15 days before conducting an eccentric exercise protocol using the non-dominant arm. A six-week washout period was required between conditions. Performance and mobility markers such as isometric peak torque (PTQ), ligament range of motion (ROM), and perceived muscle discomfort (VAS) were assessed and blood samples (CK, LDH) were obtained at 1, 24, 48, and 72 h post-exercise. No significant differences were noticed between the two conditions on any of the investigated markers, indicating that spirulina supplementation has no positive effect on isometric muscle performance or alleviation of exercise-induced muscle damage (EIMD) symptoms in the specific population.

Age-related blunting of serial sarcomerogenesis and mechanical adaptations following 4 wk of maximal eccentric resistance training

During aging, muscles undergo atrophy, which is partly accounted for by a loss of sarcomeres in series. Serial sarcomere number (SSN) is associated with aspects of muscle mechanical function including the force-length and force-velocity-power relationships; hence, the age-related loss of SSN contributes to declining performance. Training emphasizing eccentric contractions increases SSN in young healthy rodents; however, the ability for eccentric training to increase SSN in old age is unknown. Ten young (8 mo) and 11 old (32 mo) male Fisher344/BN rats completed 4 wk of unilateral eccentric plantar flexion training. Pre- and posttraining, the plantar flexors were assessed for the torque-frequency, passive torque-angle, and torque-velocity-power relationships. The soleus, lateral gastrocnemius (LG), and medial gastrocnemius (MG) were harvested for SSN assessment via laser diffraction, with the untrained leg used as a control. In the untrained leg/pretraining, old rats had lower SSN in the soleus, LG, and MG, lower maximum torque, power, and shortening velocity, and greater passive torque than young. Young showed increased soleus and MG SSN following training. In contrast, old had no change in soleus SSN and experienced SSN loss in the LG. Pre- to posttraining, young experienced an increase in maximum isometric torque, whereas old had reductions in maximum torque, shortening velocity, and power, and increased passive torque. Our results show that although young muscle has the ability to add sarcomeres in response to maximal eccentric training, this stimulus could be not only ineffective, but also detrimental to aged muscle leading to dysfunctional remodeling.NEW & NOTEWORTHY The loss of sarcomeres in series with age contributes to declining muscle performance. The present study investigated whether eccentric training could improve performance via serial sarcomere addition in old muscle, like in young muscle. Four weeks of maximal eccentric training induced serial sarcomere addition in the young rat plantar flexors and improved in vivo performance, however, led to dysfunctional remodeling accompanied by further impaired performance in old rats.

Cadence Modulation during Eccentric Cycling Affects Perception of Effort But Not Neuromuscular Alterations

INTRODUCTION

A recent study showed that cadence modulation during short eccentric cycling exercise affects oxygen consumption (V̇O 2 ), muscular activity (EMG), and perception of effort (PE). This study examined the effect of cadence on V̇O 2 , EMG, and PE during prolonged eccentric cycling and exercise-induced neuromuscular alterations.

METHODS

Twenty-two participants completed three sessions 2-3 wk apart: 1) determination of the maximal concentric peak power output, familiarization with eccentric cycling at two cadences (30 and 60 rpm at 60% peak power output), and neuromuscular testing procedure; 2) and 3) 30 min of eccentric cycling exercise at a cadence of 30 or 60 rpm. PE, cardiorespiratory parameters, and vastus lateralis and rectus femoris EMG were collected during exercise. The knee extensors' maximal voluntary contraction torque, the torque evoked by double stimulations at 100 Hz (Dt100) and 10 Hz (Dt10), and the voluntary activation level were evaluated before and after exercise.

RESULTS

V̇O 2 , EMG, and PE were greater at 30 than 60 rpm (all P < 0.05). Maximal voluntary contraction torque, evoked torque, and Dt10/Dt100 ratio decreased (all P < 0.01) without cadence effect (all P > 0.28). Voluntary activation level remained constant after both eccentric cycling exercises ( P = 0.87).

CONCLUSIONS

When performed at the same power output, eccentric cycling exercise at 30 rpm elicited a greater PE, EMG, and cardiorespiratory demands than pedaling at 60 rpm. Exercise-induced fatigability was similar in both eccentric cycling conditions without neural impairments, suggesting that eccentric cycling seemed to alter more specifically muscular function, such as the excitation-contraction coupling process. In a rehabilitation context, eccentric cycling at 60 rpm seems more appropriate because it will induce lower PE for similar strength loss compared with 30 rpm.

Skeletal Muscle Heat Shock Protein Content and the Repeated Bout Effect

The "Repeated Bout Effect" (RBE) occurs when a skeletal muscle is preconditioned with a few lengthening contractions (LC) prior to exposing the muscle to a greater number of LC. The preconditioning (PC) results in significantly less damage and preservation of force. Since it takes only a few LC to increase muscle heat shock protein (HSP) content, it was of interest to examine the relationship between HSPs and the RBE. To do this, one tibialis anterior (TA) muscle from Sprague-Dawley rats (n = 5/group) was preconditioned with either 0, 5, or 15 lengthening contractions (LC) and exposed to a treatment of 60 LC 48 h later. Preconditioning TA muscles with 15 LC, but not 5 LC, significantly elevated muscle αB-crystallin (p < 0.05), HSP25 (p < 0.05), and HSP72 content (p < 0.001). These preconditioned TA muscles also showed a significantly (p < 0.05) reduced loss of active torque throughout the subsequent 60 LC. While there was a trend for all preconditioned muscles to maintain higher peak torque levels throughout the 60 LC, no significant differences were detected between the groups. Morphologically, preconditioned muscles appeared to show less discernible muscle fiber damage. In conclusion, an elevated skeletal muscle HSP content from preconditioning may contribute to the RBE.

Proteomic Profiling of Muscular Adaptations to Short-Term Concentric Versus Eccentric Exercise Training in Humans

The molecular mechanisms underlying muscular adaptations to concentric (CON) and eccentric (ECC) exercise training have been extensively explored. However, most previous studies have focused on specifically selected proteins, thus, unable to provide a comprehensive protein profile and potentially missing the crucial mechanisms underlying muscular adaptation to exercise training. We herein aimed to investigate proteomic profiles of human skeletal muscle in response to short-term resistance training. Twenty young males were randomly and evenly assigned to two groups to complete a 4-week either ECC or CON training program. Measurements of body composition and physiological function of the quadriceps femoris were conducted both before and after the training. Muscle biopsies from the vastus lateralis of randomly selected participants (five in ECC and four in CON) of both before and after the training were analyzed using the liquid-chromatography tandem mass spectrometry in combination with bioinformatics analysis. Neither group presented a significant difference in body composition or leg muscle mass; however, muscle peak torque, total work, and maximal voluntary contraction were significantly increased after the training in both groups. Proteomics analysis revealed 122 differentially abundant proteins (DAPs; p value < 0.05 & fold change >1.5 or <0.67) in ECC, of which the increased DAPs were mainly related to skeletal muscle contraction and cytoskeleton and enriched specifically in the pentose phosphate pathway, extracellular matrix-receptor interaction, and PI3K-Akt signaling pathway, whereas the decreased DAPs were associated with the mitochondrial respiratory chain. One hundred one DAPs were identified in CON, of which the increased DAPs were primarily involved in translation/protein synthesis and the mitochondria respiratory, whereas the decreased DAPs were related to metabolic processes, cytoskeleton, and de-ubiquitination. In conclusion, the 4-week CON and ECC training resulted in distinctly different proteomic profiles, especially in proteins related to muscular structure and metabolism.

Acute Response to Training after Returning from the Off-Season in Elite Rugby League Athletes

The purposes of this study were to quantify the physiological response to the initial two-week preseason period in elite male rugby league (RL) athletes, and to determine if a repeated bout effect (RBE) occurs. Eighteen RL players were monitored for the initial two-week preseason period. Blood samples were collected on days (D)1, D2, D4, D5, D8, D9, D11 and D12 to measure creatine kinase (CK). Neuromuscular power was assessed on D1, D5, D8 and D12. During field-based sessions, the external training load was quantified using global positioning system technology, whilst the internal load was quantified using the training impulse and the session rating of perceived exertion. Resistance-based gym session volume was quantified by total repetitions x weight lifted. Perceived measures of fatigue and muscle soreness were assessed on all training days. Two-way (day x week) repeated measures analysis of variance and Bonferroni's corrected post-hoc tests identified significant changes. There were no significant changes in CK activity (649.2 ± 255.0 vs. 673.8 ± 299.1 µL; p = 0.63) or internal training load measures from week 1 to week 2. External training load measures including total distance (4138.1 ± 198.4 vs. 4525.0 ± 169.2 m; p < 0.001) and repeated high-intensity efforts (12.6 ± 1.8 vs. 17.5 ± 1.8 au; p < 0.001) significantly increased in week 2 compared to week 1. Internal training loads and CK activity did not change in response to an increase in external training loads during the initial preseason. The current results provide support for a 'real world' perspective of the RBE phenomenon that may be more applicable for team sport practitioners.

Effects of far-infrared radiation lamp therapy on recovery from a simulated soccer-match in elite female soccer players

We investigated the effects of far-infrared radiation (FIR) lamp therapy on changes in muscle damage and performance parameters following six sets of 15-min Loughborough intermittent shuttle test (LIST), a simulated soccer match. Twenty-four elite female soccer players (20-24 y) were assigned into FIR or sham treatment group (n = 12/group). The participants received a 60-min FIR or sham treatment (30 min per muscle) over knee extensors (KE) and flexors (KF) at 2, 25, 49, 73, and 97 h post-LIST. Maximal voluntary isometric contraction (MVC) torque and muscle soreness of the KE and KF, plasma creatine kinase (CK) activity as muscle damage markers, and several performance parameters including countermovement jump (CMJ) and Yo-Yo intermittent recovery test level 1 (YYIR1) were measured before and 1, 24, 48, 72, 96, and 120 h post-LIST. Changes in the measures were compared between groups by a mixed-design two-way ANOVA. The running distance covered during LIST and changes in the measures at 1-h post-LIST (before the treatment) were similar (p = 0.118-0.371) between groups. Changes in muscle damage markers at 24-120 h post-LIST were smaller (p < 0.05, η2 = 0.208-0.467) for the FIR (e.g., MVC-KE torque decrease at 48-h post-LIST: -1 ± 2%, peak KE soreness: 16 ± 10 mm, peak CK: 172 ± 42 IU/L) than sham group (-11 ± 9%, 33 ± 7 mm, 466 ± 220 IU/L, respectively). Performance parameters recovered faster (p < 0.05, η2 = 0.142-0.308) to baseline for the FIR (e.g., decreases at 48-h post-LIST; CMJ: 0 ± 1%, YYIR1: 0 ± 1%) than sham group (-6 ± 2%, -9 ± 6%, respectively). These results suggest that the FIR lamp therapy was effective for enhancing recovery from a soccer match.

Reduction in systemic muscle stress markers after exercise-induced muscle damage following concurrent training and supplementation with specific collagen peptides - a randomized controlled trial

Introduction

Collagen peptide supplementation in conjunction with exercise has been shown to improve structural and functional adaptations of both muscles and the extracellular matrix. This study aimed to explore whether specific collagen peptide (SCP) supplementation combined with a concurrent training intervention can improve muscular stress after exercise-induced muscle damage, verified by reliable blood markers.

Methods

55 sedentary to moderately active males participating in a concurrent training (CT) intervention (3x/week) for 12 weeks were administered either 15 g of SCP or placebo (PLA) daily. Before (T1) and after the intervention (T2), 150 muscle-damaging drop jumps were performed. Blood samples were collected to measure creatine kinase (CK), lactate dehydrogenase (LDH), myoglobin (MYO) and high-sensitivity C-reactive protein (hsCRP) before, after, and at 2 h, 24 h and 48 h post exercise.

Results

A combination of concurrent training and SCP administration showed statistically significant interaction effects, implying a lower increase in the area under the curve (AUC) of MYO (p = 0.004, ηp2 = 0.184), CK (p = 0.01, ηp2 = 0.145) and LDH (p = 0.016, ηp2 = 0.133) in the SCP group. On closer examination, the absolute mean differences (ΔAUCs) showed statistical significance in MYO (p = 0.017, d = 0.771), CK (p = 0.039, d = 0.633) and LDH (p = 0.016, d = 0.764) by SCP supplementation.

Conclusion

In conclusion, 12 weeks of 15 g SCP supplementation combined with CT intervention reduced acute markers of exercise-induced muscle damage and improved post-exercise regenerative capacity, as evidenced by the altered post-exercise time course. The current findings indicate that SCP supplementation had a positive effect on the early phase of muscular recovery by either improving the structural integrity of the muscle and extracellular matrix during the training period or by accelerating membrane and cytoskeletal protein repair.

Clinical trial registration

https://www.clinicaltrials.gov/study/NCT05220371?cond=NCT05220371&rank=1, NCT05220371.

Recovery kinetics following sprint training: resisted versus unresisted sprints

PURPOSE

To determine the recovery kinetics of performance and exercise-induced muscle damage following different sprint-training protocols.

METHODS

In a crossover design, ten male and female athletes (20.6 ± 2.4 years) performed 2 × (3 × 20 m: 2 min rest) and 1× (3 × 30 m: 3 min rest) of: (a) unresisted sprints (UST), (b) resisted sprints with 10% of body mass (BM) load (RST10), (c) resisted sprints with 20% BM load (RST20), against a control trial (no-training).

RESULTS

Blood lactate (mmol/L) increased post-training versus pre-training in all sprint-training trials (6.7 ± 2.4 vs 1.2 ± 0.2, 5.6 ± 2.4 vs 1.3 ± 0.3, 7.3 ± 2.7 vs 1.2 ± 0.3, in UST, RST10, RST20, respectively), as did creatine kinase (U/L) 24 h, 48 h and 72 h post-training (UST: 251 ± 173, 238 ± 154, 209 ± 115 vs 155 ± 9, RST10: 252 ± 134, 240 ± 83, 218 ± 103 vs 164 ± 106; RST20: 237 ± 133, 323 ± 303, 262 ± 184 vs 179 ± 106, respectively). DOMS of knee-extensors (KE) and knee-flexors (KF) increased post-training up to 72 h in all sprint-training trials versus pre-training (ranging from 1.6 ± 1.3 to 3.8 ± 2.8 vs 1.0 ± 0, respectively). Eccentric torque (N m) of the KE of the non-dominant limb, decreased 24 h post-training versus pre-training in all sprint-training trials (UST: 249 ± 49 vs 266 ± 54; RST10: 229 ± 52 vs 273 ± 72; RST20: 253 ± 6 vs 262 ± 56), as did that of the KF of the dominant limb (UST: 135 ± 29 vs 144 ± 26; RST10: 130 ± 29 vs 140 ± 25; RST20: 139 ± 33 vs 142 ± 26). 10-m sprint-time (s) increased 48 h post-training versus pre-training (1.81 ± 0.15 vs 1.77 ± 0.11), and 30-m sprint-time increased 24 h, 48 h, 72 h post-training versus pre-training (4.35 ± 0.36, 4.40 ± 0.44, 4.33 ± 0.41 vs 4.21 ± 0.34, respectively), only in RST20.

CONCLUSIONS

Unresisted and resisted sprint-training induces prolonged reduction of muscle strength (24 h), and sprinting performance (72 h), associated with prolonged increase of DOMS and CK (72 h).

Immediate crossover fatigue after unilateral submaximal eccentric contractions of the knee flexors involves peripheral alterations and increased global perceived fatigue

After a unilateral muscle exercise, the performance of the non-exercised contralateral limb muscle can be also impaired. This crossover fatigue phenomenon is still debated in the literature and very few studies have investigated the influence of eccentric contractions. This study was designed to assess neuromuscular adaptations involved in the crossover fatigue of the non-exercised contralateral knee flexor muscles. Seventeen healthy young men performed a unilateral submaximal eccentric exercise of the right knee flexors until a 20% reduction in maximal voluntary isometric contraction torque was attained in the exercised limb. Before (PRE), immediately after exercise cessation (POST) and 24 hours later (POST24), neuromuscular function and perceived muscle soreness were measured in both the exercised limb and non-exercised limb. In addition, global perceived fatigue was assessed at each measurement time. At POST, significant reductions in maximal voluntary isometric contraction were observed in the exercised limb (-28.1%, p < 0.001) and in the non-exercised limb (-8.5%, p < 0.05), evidencing crossover fatigue. At POST, voluntary activation decreased in the exercised limb only (-6.0%, p < 0.001), while electrically evoked potentiated doublet torque was impaired in both the exercised limb and the non-exercised limb (-11.6%, p = 0.001). In addition, global perceived fatigue significantly increased at POST (p < 0.001). At POST24, all measured variables returned to PRE values, except for perceived muscle soreness scores exhibiting greater values than PRE (p < 0.05). A possible cumulative interaction between peripheral alterations and global perceived fatigue may account for the immediate crossover fatigue observed in the non-exercised limb.

Neurochemical mechanism of muscular pain: Insight from the study on delayed onset muscle soreness

We reviewed fundamental studies on muscular pain, encompassing the characteristics of primary afferent fibers and neurons, spinal and thalamic projections, several muscular pain models, and possible neurochemical mechanisms of muscle pain. Most parts of this review were based on data obtained from animal experiments, and some researches on humans were also introduced. We focused on delayed-onset muscle soreness (DOMS) induced by lengthening contractions (LC), suitable for studying myofascial pain syndromes. The muscular mechanical withdrawal threshold (MMWT) decreased 1-3 days after LC in rats. Changing the speed and range of stretching showed that muscle injury seldom occurred, except in extreme conditions, and that DOMS occurred in parameters without muscle damage. The B2 bradykinin receptor-nerve growth factor (NGF) route and COX-2-glial cell line-derived neurotrophic factor (GDNF) route were involved in the development of DOMS. The interactions between these routes occurred at two levels. A repeated-bout effect was observed in MMWT and NGF upregulation, and this study showed that adaptation possibly occurred before B2 bradykinin receptor activation. We have also briefly discussed the prevention and treatment of DOMS.

Effects of single and repeated bouts of flywheel exercise on jump performance and muscle damage in athletes and non athletes

BACKGROUND

Although recent studies have investigated the effects of flywheel (FW) training on muscle function, the effects of transient FW exercise on jump performance in athletes are unknown. This study examined the effects of single and repeated bouts of FW squat exercises on jump performance and muscle damage in male collegiate basketball players.

METHODS

The participants were 10 healthy college-age men (nonathletes) and 11 male basketball players (athletes). The intervention involved 100 squat exercises (10 repetitions × 10 sets) using an FW device. To examine the repeated-bout effects, the protocol was conducted again after a 2-week interval. Squat jumps, countermovement jumps, drop jumps, and rebound jumps were evaluated as jump performance, while isometric maximal voluntary contraction (MVC) torque in knee extension, muscle soreness, range of motion, thigh circumference, muscle thickness, and echo intensity were evaluated as markers of muscle damage. Measurements were taken at baseline, immediately after exercise, 24 h later, and 72 h later.

RESULTS

The jump performance of nonathletes decreased after exercise (p < 0.05), while that of the athletes did not. The results were similar for muscle soreness. MVC torque decreased significantly after the first exercise in both groups (p < 0.05) and was significantly lower in the nonathletes versus athletes. Significant repeated-bout effects were found for muscle soreness in nonathletes but not athletes.

CONCLUSIONS

These results suggest that a single bout of FW exercise reduces jump performance in male nonathletes but not basketball players.

Effects of Minimal-Equipment Resistance Training and Blood Flow Restriction on Military-Relevant Performance Outcomes

ABSTRACT

Cintineo, HP, Chandler, AJ, Mastrofini, GF, Lints, BS, McFadden, BA, and Arent, SM. Effects of minimal-equipment resistance training and blood flow restriction on military-relevant performance outcomes. J Strength Cond Res 38(1): 55-65, 2024-This study compared minimal-equipment resistance training (RT) with and without blood flow restriction (BFR) to traditional-equipment RT on performance and body composition changes over 6 weeks. Reserve officers' training corps cadets and midshipmen (N = 54, 40.7% female) were randomized into traditional-equipment RT (TRAD), minimal-equipment RT (MIN), or minimal-equipment RT with BFR (MIN + BFR). Performance and body composition were assessed pretraining and post-training, and measures of intensity and workload were evaluated throughout. Performance assessments included the army combat fitness test (ACFT), countermovement vertical jump, 3RM bench press, and V̇O2max; body composition measures included body fat percentage, fat-free mass, and muscle and tendon thickness. All groups trained 4 days per week after a full-body routine. Data were analyzed by mixed-effects models (α = 0.05). Group-by-time interactions for 3RM deadlift and 3RM bench press (p < 0.004) showed larger improvements for TRAD compared with MIN and MIN + BFR. Time main effects for all other performance variables, body fat percentage, fat-free mass, and muscle thickness (p ≤ 0.035) indicated improvements in all groups. A group-by-time interaction for blood lactate (p < 0.001) and group main effects for heart rate (p < 0.001) and workload variables (p < 0.008) indicated higher intensity and workload for MIN and MIN + BFR compared with TRAD. A sex-by-time interaction for 3RM deadlift (p = 0.008) and sex-by-group-by-time interaction for 3RM bench press (p = 0.018) were also found. Minimal-equipment RT improved performance and body composition, although strength improvements were greater with traditional equipment. Minimal-equipment RT and minimal-equipment RT with BFR exhibited higher exertion levels than TRAD, although adaptations were similar. Overall, individuals can improve performance and body composition using portable, field-expedient RT equipment.

Effect of blood flow restriction with low-load exercise on muscle damage in healthy adults: A systematic review of randomized controlled trials

INTRODUCTION

Blood flow restriction (BFR) is a relatively new rehabilitative technique and low-load exercise combined with BFR (LL-BFR) can increase muscle strength and muscle mass. However, it is currently unknown whether LL-BFR causes muscle damage. Therefore, the aim of this study is to investigate the effects of LL-BFR on muscle damage and provide recommendations for sports training and physical exercise.

MATERIALS AND METHODS

A systematic search was conducted using PubMed, Web of Science, Medline, Cochrane Library and Physiotherapy Evidence Database (PEDro) with a cut-off of March 2022. Randomized controlled trials (RCTs) and English-language studies were selected. Two independent assessors used the PEDro scoring scale to evaluate the methodological quality and risk of bias of the included studies.

RESULTS

Of the 2935 articles identified, 15 RCTs were included in this systematic review. Two studies demonstrated that LL-BFR could induce muscle damage in healthy individuals; however, two studies presented contrasting findings in the short term. Four studies found that no muscle damage occurred after LL-BFR in the long term. The remaining seven articles showed that it was unclear if LL-BFR could cause muscle damage, regardless of whether these participants were trained or not.

CONCLUSION

Although LL-BFR may induce muscle damage within 1 week, it will help gain long-term muscle strength and muscle hypertrophy. However, the lack of sufficient evidence on the effect of LL-BFR on muscle damage in clinical practice warrants additional RCTs with large sample sizes in the future.

Effects of low-load blood flow restriction on the venous system in comparison to traditional low-load and high-load exercises

Purpose: Blood-Flow-Restriction (BFR) training provides the ability to achieve hypertrophy effects even though only light mechanical loads are applied. However, its impact on venous pressures and function are still unknown. Therefore, the present study investigates the influence of BFR-training on intravascular venous pressure and venous function in comparison to control exercises with low or high mechanical loads. Methods: In a randomized cross-over design, ten healthy men (27.6 ± 6.4 years) underwent three trials of unilateral knee-extensor exercise with three different training protocols, low-load- (LL-RT, 30% of the individual 1-repetition-maximum, 1RM), low-load BFR- (LL-BFR-RT, 30% 1RM, 50% limb occlusion pressure, LOP) and high-load resistance exercise (HL-RT, 75% 1RM). Exercise protocols contain about four sets of knee extension exercise (Range-of-Motion: 0-0-95°), separated by 60 s of rest. Each set was performed until volitional muscle failure. For analysis of changes in intravascular venous pressures and venous function, a venous catheter was placed at the exercising leg before each trial. Whereas venous pressures were recorded throughout the exercise trials, phlebodynamometric investigations were performed before and after each trial. Furthermore, subjective pain perception during and after exercise was accessed by visual analogue scale. One-way ANOVA was used to assess mean differences between training protocols, while two-way repeated-measures ANOVA (rANOVA; time x condition) was performed to compare changes in measures over time among conditions. Data were given as means ± standard deviation (SD). Results: In comparison to the exercise trials without venous occlusion, total workload was significantly lower in the LL-BFR-RT (LL-RT: 1745 ± 604 kg vs LL-BFR-RT: 1274 ± 237 kg vs HL-RT: 1847 ± 367 kg, p = 0.004) without indicating statistical differences in venous pressures during the exercise sets (interaction: p = 0.140) or pain perception (interaction: p = 0.574). Similarly, phlebodynamometric assessment of venous function (e.g. refill-time of the venous system pre-vs. post exercise trials-LL-RT: 29.7 ± 11.0 s vs 25.5 ± 9.6 s, LL-BFR-RT: 26.6 ± 13.0 s vs 27.3 ± 13.8 s, HL-RT: 25.9 ± 10.9 s vs 23.1 ± 8.2 s) revealed no time (p = 0.156), condition effect (p = 0.802) or their interactions (p = 0.382). Conclusion: The present study is the first one describing the acute effects of LL-BFR-RT to muscle failure on venous pressures and function in comparison to a LL- and HL-RT in the lower limbs. In contrast to the existing literature, LL-BFR-RT does not elevate the venous pressures during exercise higher than a comparative exercise without BFR and does not show any adverse effects on venous function after the exercise.

The effect of medical grade compression garments on the repeated-bout effect in non-resistance-trained men

NEW FINDINGS

What is the central question of this study? What are the effects of compression garments on recovery from unaccustomed damaging exercise and subsequent protective adaptations? What is the main finding and its importance? Compression did not influence recovery, but was associated with blunted protective adaptations for isokinetic performance, which were completely absent at high velocities. Based on these findings, the use of compression garments for recovery would not be recommended following unaccustomed exercise, particularly if the maintenance of high-velocity performance following exercise-induced muscle damage is desirable.

ABSTRACT

Whilst compression garments (CG) may enhance recovery from exercise-induced muscle damage (EIMD), many recovery strategies can attenuate adaptative responses. Therefore, the effects of CG on recovery from EIMD, and the rapid protective adaptations known as the repeated bout effect (RBE) were investigated. Thirty-four non-resistance-trained males (18-45 years) randomly received class II medical-grade CG or placebo for 72 h following eccentrically-focused lower-body exercise, in a double-blind, randomised controlled trial. Indices of EIMD were assessed at baseline, 0, 24, 48 and 72 h post-exercise, before exercise and testing were repeated after 14 days. Results were analysed using a three-way (time × condition × bout) linear mixed-effects model. Exercise impaired isometric and isokinetic strength, with soreness and thigh circumference elevated for 72 h (P < 0.001). Compression did not enhance recovery (P > 0.05), despite small to moderate effect sizes (ES, reported alongside 90% confidence intervals) for isokinetic strength (ES from 0.2 [-0.41, 0.82] to 0.65 [0.03, 1.28]). All variables recovered faster after the repeated bout (P < 0.005). However, RBE for peak isokinetic force was impaired in CG at 60° s-1 (group × bout interaction: χ2  = 4.24, P = 0.0395; ES = -0.56 [-1.18, 0.07]) and completely absent at 120° s-1 (χ2  = 16.2, P < 0.001, ES = -0.96 [-1.61, -0.32]) and 180° s-1 (χ2  = 10.4, P = 0.001, ES = -0.72 [-1.35, -0.09]). Compression blunted RBE at higher isokinetic velocities without improving recovery in non-resistance-trained males, potentially contraindicating their use following unaccustomed exercise in this population.

More than energy cost: multiple benefits of the long Achilles tendon in human walking and running

Elastic strain energy that is stored and released from long, distal tendons such as the Achilles during locomotion allows for muscle power amplification as well as for reduction of the locomotor energy cost: as distal tendons perform mechanical work during recoil, plantar flexor muscle fibres can work over smaller length ranges, at slower shortening speeds, and at lower activation levels. Scant evidence exists that long distal tendons evolved in humans (or were retained from our more distant Hominoidea ancestors) primarily to allow high muscle-tendon power outputs, and indeed we remain relatively powerless compared to many other species. Instead, the majority of evidence suggests that such tendons evolved to reduce total locomotor energy cost. However, numerous additional, often unrecognised, advantages of long tendons may speculatively be of greater evolutionary advantage, including the reduced limb inertia afforded by shorter and lighter muscles (reducing proximal muscle force requirement), reduced energy dissipation during the foot-ground collisions, capacity to store and reuse the muscle work done to dampen the vibrations triggered by foot-ground collisions, reduced muscle heat production (and thus core temperature), and attenuation of work-induced muscle damage. Cumulatively, these effects should reduce both neuromotor fatigue and sense of locomotor effort, allowing humans to choose to move at faster speeds for longer. As these benefits are greater at faster locomotor speeds, they are consistent with the hypothesis that running gaits used by our ancestors may have exerted substantial evolutionary pressure on Achilles tendon length. The long Achilles tendon may therefore be a singular adaptation that provided numerous physiological, biomechanical, and psychological benefits and thus influenced behaviour across multiple tasks, both including and additional to locomotion. While energy cost may be a variable of interest in locomotor studies, future research should consider the broader range of factors influencing our movement capacity, including our decision to move over given distances at specific speeds, in order to understand more fully the effects of Achilles tendon function as well as changes in this function in response to physical activity, inactivity, disuse and disease, on movement performance.

Contralateral versus ipsilateral protective effect against muscle damage of the elbow flexors and knee extensors induced by maximal eccentric exercise

The present study compared the ipsilateral repeated bout effect (IL-RBE) and contralateral repeated bout effect (CL-RBE) of the elbow flexors (EF) and knee flexors (KF) for the same interval between bouts to shed light on their mechanisms. Fifty-two healthy sedentary young (20-28 years) men were randomly assigned to the IL-EF, IL-KF, CL-EF, and CL-KF groups (n = 13/group). Thirty maximal eccentric contractions of the EF were performed in IL-EF and CL-EF, and 60 maximal eccentric contractions of the KF were performed in IL-KF and CL-KF, with a 2-week interval between bouts. Changes in muscle damage markers such as maximal voluntary contraction (MVC) torque, muscle soreness, and plasma creatine kinase activity, and proprioception measures before to 5 days post-exercise were compared between groups. Changes in all variables were greater (p < 0.05) after the first than second bout for all groups, and the changes were greater (p < 0.05) for the EF than KF. The changes in all variables after the second bout were greater (p < 0.05) for the CL than IL condition for both EF and KF. The magnitude of the average protective effect was similar between CL-EF (33%) and CL-KF (32%), but slightly greater (p < 0.05) for IL-EF (67%) than IL-KF (61%). These demonstrate that the magnitude of CL-RBE relative to IL-RBE was similar between the EF and KF (approximately 50%), regardless of the greater muscle damage for the EF than KF. It appears that the CL-RBE is more associated with neural adaptations at cerebrum, cerebellum, interhemispheric inhibition, and coricospinal tract, but the IL-RBE is induced by additional adaptations at muscles.

The Repeated Bout Effect of Multiarticular Exercises on Muscle Damage Markers and Physical Performances: A Systematic Review and Meta-Analyses

ABSTRACT

Doma, K, Matoso, B, Protzen, G, Singh, U, and Boullosa, D. The repeated bout effect of multiarticular exercises on muscle damage markers and physical performances: a systematic review and meta-analyses. J Strength Cond Res 37(12): 2504-2515, 2023-This systematic review and meta-analysis compared muscle damage markers and physical performance measures between 2 bouts of multiarticular exercises and determined whether intensity and volume of muscle-damaging exercises affected the outcomes. The eligibility criteria consisted of (a) healthy male and female adults; (b) multiarticular exercises to cause muscle damage across 2 bouts; (c) outcome measures were compared at 24-48 hours after the first and second bouts of muscle-damaging exercise; (d) at least one of the following outcome measures: creatine kinase (CK), delayed onset of muscle soreness (DOMS), muscle strength, and running economy. Study appraisal was conducted using the Kmet tool, whereas forest plots were derived to calculate standardized mean differences (SMDs) and statistical significance and alpha set a 0.05. After screening, 20 studies were included. The levels of DOMS and CK were significantly greater during the first bout when compared with the second bout at T24 and T48 (p < 0.001; SMD = 0.51-1.23). Muscular strength and vertical jump performance were significantly lower during the first bout compared with the second bout at T24 and T48 (p ≤ 0.05; SMD = -0.27 to -0.40), whereas oxygen consumption and rating of perceived exertion were significantly greater during the first bout at T24 and T48 (p < 0.05; SMD = 0.28-0.65) during running economy protocols. The meta-analyses were unaffected by changes in intensity and volume of muscle-damaging exercises between bouts. Multiarticular exercises exhibited a repeated bout effect, suggesting that a single bout of commonly performed exercises involving eccentric contractions may provide protection against exercise-induced muscle damage for subsequent bouts.

Influence of specific collagen peptides and 12-week concurrent training on recovery-related biomechanical characteristics following exercise-induced muscle damage-A randomized controlled trial

Introduction

It has been shown that short-term ingestion of collagen peptides improves markers related to muscular recovery following exercise-induced muscle damage. The objective of the present study was to investigate whether and to what extent a longer-term specific collagen peptide (SCP) supplementation combined with a training intervention influences recovery markers following eccentric exercise-induced muscle damage.

Methods

Fifty-five predominantly sedentary male participants were assigned to consume either 15 g SCP or placebo (PLA) and engage in a concurrent training (CT) intervention (30 min each of resistance and endurance training, 3x/week) for 12 weeks. Before (T1) and after the intervention (T2), eccentric muscle damage was induced by 150 drop jumps. Measurements of maximum voluntary contraction (MVC), rate of force development (RFD), peak RFD, countermovement jump height (CMJ), and muscle soreness (MS) were determined pre-exercise, immediately after exercise, and 24 and 48 h post-exercise. In addition, body composition, including fat mass (FM), fat-free mass (FFM), body cell mass (BCM) and extracellular mass (ECM) were determined at rest both before and after the 12-week intervention period.

Results

Three-way mixed ANOVA showed significant interaction effects in favor of the SCP group. MVC (p = 0.02, ηp2 = 0.11), RFD (p < 0.01, ηp2 = 0.18), peak RFD (p < 0.01, ηp2 = 0.15), and CMJ height (p = 0.046, ηp2 = 0.06) recovered significantly faster in the SCP group. No effects were found for muscle soreness (p = 0.66) and body composition (FM: p = 0.41, FFM: p = 0.56, BCM: p = 0.79, ECM: p = 0.58).

Conclusion

In summary, the results show that combining specific collagen peptide supplementation (SCP) and concurrent training (CT) over a 12-week period significantly improved markers reflecting recovery, specifically in maximal, explosive, and reactive strength. It is hypothesized that prolonged intake of collagen peptides may support muscular adaptations by facilitating remodeling of the extracellular matrix. This, in turn, could enhance the generation of explosive force.

Clinical trial registration

ClinicalTrials.gov, identifier ID: NCT05220371.