Isometric training and long-term adaptations: Effects of muscle length, intensity, and intent: A systematic review

Muscle Swelling and Neuromuscular Responses Following Blood Flow Restricted Exercise in Untrained Women

Purpose: There is conflicting evidence related to the prevalence and magnitude of exercise-induced muscle damage (EIMD) following four sets to volitional failure with BFR (BFR-F) or 75 total repetitions with BFR (1 × 30, 3 × 15, BFR-75). The purpose of this investigation was to examine muscle swelling, peak torque, and neuromuscular responses following BFR-75 and BFR-F. Methods: Thirteen untrained women completed unilateral isokinetic (120°s-1) leg extensions concentric-eccentric at 30% of their maximal voluntary isometric contraction (MVIC) using BFR-75 and BFR-F protocols, separated by 15 minutes. Ultrasound was used to assess muscle thickness, cross sectional area, and echo intensity of the rectus femoris and vastus lateralis before, 0-, 24-, 48-, 72-, and 96-hours post-exercise. Peak torque and surface electromyography (sEMG) were recorded during MVICs before, 24-, 48-, 72-, and 96-hours post-exercise to determine sEMG amplitude, frequency, and neuromuscular efficiency. Results: There were no differences between conditions. Collapsed across conditions, muscle thickness and cross-sectional area increased at 0-hours for the rectus femoris (2.5 ± 0.4, 2.8 ± 0.4 cm, 10.6 ± 1.8, 12.1 ± 1.8 cm2, respectively) and vastus lateralis (2.1 ± 0.5, 2.5 ± 0.7 cm; 22.2 ± 3.9, 25.1 ± 4.5 cm2, respectively), but returned to baseline at 24-hours. There were no changes in echo intensity, sEMG amplitude, sEMG frequency, or neuromuscular efficiency. MVIC peak torque increased relative to pre-exercise at 24-, 48-, 72-, and 96-hours (159.9 ± 34.9, 171.4 ± 30.1-179.1 ± 35.6 Nm). Conclusion: These results suggest that BFR-75 and BFR-F did not cause EIMD but caused an acute increase in muscle swelling that returned to baseline 24-hours post-exercise.

Protein supplementation optimizes muscle strength and hypertrophic responses induced by low-load training with blood flow restriction in resistance-trained individuals

BACKGROUND & AIMS

Low-load blood flow restriction (LL-BFR) training induces favorable changes in muscle hypertrophy and strength. However, the potential additive effect of LL-BFR and protein supplementation on these outcomes remains unclear.

METHODS

Twenty-four recreationally resistance-trained men were randomly assigned to either a protein (PRO) or placebo (PLA) supplementation group in a 2:1 ratio. After being submitted to maximum dynamic strength (1-RM) and elbow flexors muscles cross-sectional area (EFCSA) assessments at baseline, participants were enrolled in a 3-week unilateral LL-BFR training (4 days per week, 4 sets of 15 repetitions, 30 % 1-RM) for the elbow flexors muscles in the incline dumbbell curl exercise. Psychological outcomes (rate of perceived exertion, pain and muscle soreness) were obtained at the first and last training session. EFCSA and 1-RM were reassessed after LL-BFR, with EFCSA being assessed at 45 %, 65 % and 85 % of humerus length.

RESULTS

Psychological responses to LL-BFR improved in PRO and PLA (both p < 0.05), with no significant between-group differences (all comparisons, p > 0.05). A significant improvement in 1-RM was detected for PRO (+7.2 %, p = 0.0002), but not PLA (+3.5 %, p = 0.156). PRO experienced significant increases in EFCSA at 45 % (+7.5 %, p = 0.021), 65 % (+5.2 %, p = 0.033) and 85 % lengths (+8.4 %, p = 0.002), while PLA experienced increases only at the 85 % length (+5.9 %, p = 0.045). Absolute increases in 1-RM were greater for PRO vs. PLA (p = 0.039), whereas increases in EFCSA tended to be greater for PRO vs. PLA at 45 % (p = 0.086) and 65 % lengths (p = 0.072).

CONCLUSION

Our results showed that protein supplementation optimized the LL-BFR-induced muscle strength and hypertrophy improvements in trained individuals under comparable psychological responses.

Integrating Motor Learning Principles into Muscle Force and Balance Control

The principles of specificity and similarity play a crucial role in supporting the transfer and retention of motor performance in general sports training. Nevertheless, the extent to which force control ability translates into dynamic performance remains unclear. We aimed to investigate the effect of force control training on the transfer and retention of balance control in 18 young individuals. The force control training utilized a visual-guided force tracking task with either a uniform or non-uniform sinusoidal wave in ankle plantar flexors (PF). Postural stability was assessed by measuring the center of pressure (COP) in a single-leg standing posture. Despite consistent repetitions, no significant differences in COP parameters were observed between the pre- and post-training assessments. However, significant differences were noted between the pre-training assessments and the post-training assessments conducted one week later, utilizing a randomized order. Shifting from a regimen of constant repetition to a randomized order has a positive impact on the transfer and retention of acquired motor skills. This approach, based on the motor learning theory, holds promise for enhancing the motor performance of athletes and patients undergoing rehabilitation.

Acute effects of isometric conditioning activity with different distribution contraction on countermovement jump performance in resistance trained participants

The aim of this study was to compare the effects of 3 sets of isometric conditioning activity (ICA), each with an equal total duration (9 s per set) but with different distributions contractions, on force production during ICA and subsequent countermovement jump (CMJ) performance. Fifteen resistance-trained males participated in this study (age: 22.1 ± 2.4 years; body mass: 85.1 ± 9.7 kg; height: 181.3 ± 6.5 cm; relative one-repetition maximum (1RM) in back squat: 1.59 ± 0.32 kg/kg of body mass). Participants completed 3 conditions, each consisting of ICA in the half-back squat with a pushing isometric muscle action (PIMA) position at a 120-degree knee angle against an immovable barbell, differing in repetition distribution: 3 sets of 9 repetitions lasting 1 s each (SUST-1), 3 sets of 3 repetitions lasting 3 s each (SUST-3), 3 sets of single repetitions lasting 9 s (SUST-9), and a control condition (CTRL) without ICA. A 1-minute rest was allowed between sets. Approximately 3 min pre-ICA and at 15 s, 3-, 6-, 9-, and 12-minutes post-ICA, the CMJ performance was assessed. Moreover, peak force (PF) production, and force generated at 100 (Force100) and 200 ms (Force200) during each ICA were evaluated. A two-way repeated measures ANOVA indicated a main effect of time on CMJ height (F = 2.674; p = 0.029; ηp²=0.171) but did not show significant differences between conditions (F = 0.934; p = 0.434; ηp²=0.067) or interactions (F = 0.826; p = 0.648; ηp²=0.060). Post-hoc comparisons indicated a significant decrease in CMJ height at the 9th minute compared to the 3rd minute (35.7 ± 5.6 cm vs. 36.8 ± 5.5 cm post-CA; d = 0.161; p = 0.048). In addition, no significant interactions or main effects were found for CMJ contraction time, PF and Force100 during ICA. However, a main effect of condition was demonstrated on Force200 (F = 19.181; p < 0.001; ηp²= 0.013). Post-hoc comparisons revealed higher Force200 values in SUST-1 (mean difference [MD] = 549 ± 137 N; d = 1.049; p < 0.001) and SUST-3 (MD = 348 ± 112 N; d = 0.665; p = 0.002) compared to the SUST-9 condition. None of the ICAs used in the present study had any effect on the CMJ performance. However, the significantly higher Force200 values noted in the SUST-1, and SUST-3 conditions compared to the SUST-9 condition suggest that the specific distributions of isometric contraction influence the force generated during their execution.

From full to partials: Investigating the impact of range of motion training on maximum isometric action, and muscle hypertrophy in young women

We compared maximum voluntary isometric action (MVIA), electromyographic (EMG) amplitude, and hypertrophy of rectus femoris (RF) and vastus lateralis (VL) between groups training in different ranges of motion (ROM). Fifty untrained women were randomised into control group (CON) or to perform knee extension exercise in one of the following groups (0°=extended knee): Full ROM (FULLROM:100°-30°), Initial ROM (INITIALROM:100°-65°), Final ROM (FINALROM:65°-30°), and Varied ROM (VARROM: alternating between INITIALROM and FINALROM). Pre- and post-training assessments included MVIA at 30º, 65º and 100º of knee flexion, during which EMG amplitude of RF and VL was recorded. Summed changes in cross-sectional area, assessed via ultrasound, were measured at four locations along muscles. Results showed greater improvements in INITIALROM and VARROM for MVIA at 100º (20.63%-25.5%) and FINALROM and VARROM for MVIA at 30º (17.28%-17.97%) compared to other groups (-2.92%-9.83% and 0.84%-3.31%, respectively). EMG response was larger in INITIALROM than FINALROM and CON at 100º (15.84% vs -6.61%-1.16%). FINALROM had a higher EMG response than INITIALROM at 30º (4.52% vs -14.95%). For hypertrophy, INITIALROM, FULLROM, and VARROM showed greatest increases (13.20%-17%). Greater MVIA gains aligned with trained ROM, leading to better VARROM results. INITIALROM, FULLROM, and VARROM were more effective than FINALROM in hypertrophy.

Hamstring T-Junction Surgical Repair: An Elite Footballer's Return to Play Journey Through a New Football-Centered Complex Approach

Background

Hamstring strain injuries have a significant impact in football, with a high re-injury rate, particularly when the distal musculotendinous T-junction (DMTJ) is involved. In some cases, surgical repair is necessary to reduce the risk of re-injury and ensure return to play (RTP) at the pre-injury level.

Study design

Case Report.

Case description

A 24-year-old male football (soccer) player, playing in the Swiss first division, with recidivate hamstring injury, who undercame to surgical repair of DMTJ and returned to play through after 19 weeks. This case report introduces a new football-centered model divided into four main phases, showing how it guided the clinical reasoning used through the RTP process, along with MRI evaluations, clinical outcomes, global positioning system (GPS) data, and strength and power (S&P) neuromuscular testing.

Outcomes

The subject gradually returned to team training after 12 weeks and successfully returned to play after 19 weeks. The player participated in 26 official matches throughout the season, accumulating 1.323 minutes of play without reporting any symptoms at the injury site.

Conclusions

The subject had a successful return to play following the rehab model proposed in this case report, as he was involved in all the matches, and he played without any symptoms or new injuries.

Level of evidence

5.

Comparison Between Shoulder Flexed and Extended Positions in Elbow Flexion Resistance Training on Regional Hypertrophy and Maximum Strength: Preacher versus Bayesian Cable Curls

In the present study, the effects of resistance training on regional hypertrophy and maximum strength of the elbow flexor muscles were compared between elbow flexion exercises performed with different shoulder joint angles (∼50° of flexion vs. extension) while matched for resistance profiles. In a within-subject design, 15 young men (25.6 ± 2.1 y; 77.3 ± 6.8 kg; 175.1 ± 5.7 cm) underwent a resistance training program twice a week for 10 weeks (3-5 sets, 8-12RM), and their arms were dominant-side balanced, randomly assigned to one of the two conditions according to elbow flexion exercises: unilateral cable curl with shoulder flexed (Preacher curl; PREA) or unilateral cable curl with shoulder extended (Bayesian curl; BAYE). B-mode ultrasound imaging was used to measure changes in muscle thickness of the biceps brachii and brachialis at proximal, mid, and distal arm regions, and one-repetition maximum tests were completed in each respective trained exercise before and after training. Both conditions showed significant increases in muscle thickness (p < 0.05) with no significant differences between them (p > 0.05) across the biceps brachii proximal, mid, and distal regions (relative change [Hedges' g effect size]; PREA: 6%[0.51], 7%[0.49], 7%[0.53]; BAYE: 9%[0.73], 9%[0.62], 9%[0.62]) and brachialis (PREA: 10%[0.72]; BAYE: 8%[0.65]). Similarly, significant improvements in maximum strength were observed (p < 0.05), with equivalent results between conditions (PREA: 28%[0.85], BAYE: 37%[1.22]; equivalence testing, p-values = 0.061, 0.637). In conclusion, the shoulder joint angle does not seem to affect muscle hypertrophy and maximum strength gains after different elbow flexion exercises matched for resistance profiles.

Resistance exercise training improves disuse-induced skeletal muscle atrophy in humans: a meta-analysis of randomized controlled trials

BACKGROUND

This meta-analysis aimed to determine whether resistance exercise training (RET) can attenuate the loss of muscle volume and function in anti-gravitational muscles, especially quadriceps and calf muscles, during immobilization/disuse conditions.

METHODS

A comprehensive literature search was conducted to identify randomized controlled trials comparing RET vs. no exercise during immobilization/disuse. Searches were conducted in databases including Web of Science, PubMed, EBOSCO, and Cochrane Library, without imposing a time limit until 20 March, 2023. Studies reporting outcomes related to muscle volume, MVC, peak power, concentric peak force, eccentric peak force, isometric MVC torque of knee extension, isometric MVC torque of knee flexion were included. Data were pooled using random-effects models.

RESULTS

Eleven randomized controlled trials were finally included. RET elicited substantial benefits for preserving quadriceps muscle volume (n = 5, MD = 252.56, 95% CI = 151.92, 353.21, p < 0.001). RET demonstrated a statistically significant preventive effect on the reduction of MVC in both quadriceps (n = 4, MD = 338.59, 95% CI = 247.49, 429.69, p < 0.001) and calf muscles (n = 3, MD = 478.59, 95% CI = 160.42, 796.77, p < 0.01). Peak power of quadriceps muscles (n = 4, MD = 166.08, 95% CI = 28.44, 303.73, p < 0.05) and calf muscles (n = 2, MD = 176.58, 95% CI = 102.36, 250.79, p < 0.001) were elevated after RET intervention. RET significantly ameliorated the weakening of both concentric and eccentric peak force in quadriceps (concentric: n = 2, MD = 470.95, 95% CI = 355.45, 586.44, p < 0.001; eccentric: n = 1, MD = 351.51, 95% CI = 254.43, 448.58, p < 0.001) and calf muscles (concentric: n = 2, MD = 867.52, 95% CI = 548.18, 1186.86, p < 0.001; eccentric: n = 1, MD = 899.86, 95% CI = 558.17, 1241.55, p < 0.001). Additionally, the diminishing of isometric MVC torques of knee extension (n = 6, MD = 41.85, 95% CI = 20.93, 62.77, p < 0.001) and knee flexion (n = 4, MD = 13.20, 95% CI = 8.12, 18.77, p < 0.001) were enhanced significantly after RET intervention.

CONCLUSIONS

RET effectively minimized deterioration of muscle volume and muscle function during immobilization/disuse, particularly in anti-gravitational muscles. RET should be recommended to maintain muscle and neuromuscular health for spaceflight, bed rest, immobilization/disuse conditions. Further research is needed to explore the effects of RET in more diverse populations and under various disuse conditions. More high-quality research will be required to demonstrate the aforementioned benefits conclusively.

The role of stretch-shortening cycle and sex in subsequent jump tasks improvement after conditioning activity based on holding isometric muscle action

BACKGROUND

This study aimed to elucidate the effectiveness of holding isometric muscle action (HIMA) by examining its impact on vertical jump enhancement due to sex and the presence of the stretch-shortening cycle (SSC) in subsequent jump tasks.

METHODS

The sample was 63 men and 42 women aged 20-27, engaged in continuous strength training for over two years at least, without musculoskeletal injuries in the past six months, divided into experimental (EXP) and control (CON) groups for countermovement jump (CMJ) and squat jump (SQ) tests considering sex. Conditioning activity (CA) involved three sets of four seconds of full-back squats at 70% 1RM for the experimental group. Jump heights for CMJ and SJ were measured, and absolute (baseline-best) and relative (%) changes were analyzed. For statistical analysis were made with Three-Way ANOVA and Tukey-Kramer post-hoc tests to evaluate jump performance differences.

RESULTS

EXP achieved more gains than control in SQ for both sexes, and both measurement approaches (P<0.05), yet no sex differences in gains were found (P>0.05). Absolute CMJ improvements were significant in experimental men versus control (P<0.05), but relative gains were not (P>0.05). SSC presence did not differentiate SQ and CMJ improvements according to sex (P>0.05); however, the effect size was large <0.80.

CONCLUSIONS

The utility of HIMA protocol as a CA has proven to be effective in improving jump performance despite sex or SSC involvement in subsequent tasks. This study showcases the adaptability of the PAPE protocol based on isometric full-back squats with submaximal load, confirming its effectiveness in enhancing jump performance in various settings.

A comparison of maximal isometric force in the first pull, transition and second pull of the clean and their contribution to predict performance in national and international level weightlifters

This study aimed to examine differences in isometric peak force (PF) at the start of the first pull, transition, and second pull phases of the clean, and determine their contribution in explaining the variance in snatch and clean & jerk (C&J) performance. Thirty-one national and international level male and female weightlifters participated. Isometric start position pull (ISPP), isometric transition position pull (ITPP), and isometric mid-thigh pull (IMTP) PF, along with competition performance, were analysed both in absolute and allometrically scaled terms. Partial Least Squares Regression identified a single latent variable explaining 81.4% of the variance in Snatch and 79.6% in C&J. ISPP PF alone significantly contributed to explaining the variance the snatch and C&J. For allometrically scaled values, a single latent variable accounted for and 62.8% variance in Snatch and 60.7% of the variance in C&J, with ISPP PF significantly contributing to the Snatch and approached significance for C&J (p = 0.056). These results underscore the importance of evaluating maximal force in the initial lift phase and suggest that training to enhance strength in this phase may be crucial for improving weightlifting performance.

Impact of Five Weeks of Strengthening Under Blood Flow Restriction (BFR) or Supplemental Oxygen Breathing (Normobaric Hyperoxia) on the Medial Gastrocnemius

Background and Objectives: This study investigates the effects of a five-week training program on the medial gastrocnemius muscle, comparing two approaches: blood flow restriction (BFR) training and normobaric hyperoxia (oxygen supplementation). It evaluates three strengthening modalities (dynamic, isometric, and the 3/7 method) analyzing their impact on maximal voluntary contraction (MVC), muscle architecture, and perceived exertion. Methods: A total of 36 young healthy participants (21 females, 15 males) were randomized into six subgroups (n = 6 each) based on the type of contraction and oxygen condition. Training sessions (three per week) were conducted for five weeks at 30% of MVC. Measurements of MVC, muscle circumference, pennation angle, fascicle length, and perceived exertion were taken at baseline (T0), mid-protocol (T1), and post-protocol (T2). Results: All groups demonstrated significant increases in MVC after five weeks, with no notable differences between BFR and oxygen conditions. Structural changes were observed in specific subgroups: the BFR-isometric group showed increased calf circumference (p < 0.05), and the 3/7 groups exhibited significant fascicle length gains (p < 0.05). Perceived exertion was consistently higher in BFR groups compared to oxygen supplementation, particularly in dynamic exercises. Conclusions: Both BFR and oxygen supplementation are effective in enhancing strength with light loads, though they elicit different structural and perceptual responses. Oxygen supplementation may be more comfortable and less strenuous, offering a viable alternative for populations unable to tolerate BFR. Future research should focus on optimizing training parameters and exploring applications tailored to specific athletic or clinical contexts.

Oh, My Quad: A Clinical Commentary And Evidence-Based Framework for the Rehabilitation of Quadriceps Size and Strength after Anterior Cruciate Ligament Reconstruction

Quadriceps weakness after anterior cruciate ligament reconstruction (ACLR) is a well-known phenomenon, with more persistent quadriceps weakness observed after ACLR with a bone-patellar tendon-bone or quadriceps tendon autograft than with a hamstring tendon autograft. Longstanding quadriceps weakness after ACLR has been associated with suboptimal postoperative outcomes and the progression of radiographic knee osteoarthritis, making the recovery of quadriceps size and strength a key component of ACLR rehabilitation. However, few articles have been written for the specific purpose of optimizing quadriceps size and strength after ACLR. Therefore, the purpose of this review article is to integrate the existing quadriceps muscle basic science and strength training literature into a best-evidence synthesis of exercise methodologies for restoring quadriceps size and strength after ACLR, as well as outline an evidence-informed quadriceps load-progression for recovering the knee's capacity to manage the force-profiles associated with high-demand physical activity. Level of Evidence: 5.

Examining the Effects of Dynamic and Isometric Resistance Training on Knee Joint Kinetics During Unplanned Sidesteps in Elite Female Athletes

ABSTRACT

Kadlec, D, Jordan, MJ, Alderson, J, and Nimphius, S. Examining the effects of dynamic and isometric resistance training on knee joint kinetics during unplanned sidesteps in elite female athletes. J Strength Cond Res 38(12): 2079-2087, 2024-The purpose of this study was to examine the effects of a 4-week block of isometric (isometric RT ) and dynamic resistance training (dynamic RT ) on kinetic variables associated with anterior cruciate ligament (ACL) injury risk during unplanned sidesteps in elite female athletes. Twenty-one elite female athletes competing for a women's international rugby union team were recruited with 15 ( n = 15; age: 23.4 ± 4.7 years; 170.7 ± 8.4 cm; 84.4 ± 15.4 kg) completing assessment of knee flexion moment, knee valgus moment (KVM), knee internal rotation moment (KIRM), knee joint power during unplanned sidesteps, and lower limb strength before and after a 4-week intervention. Linear mixed effects models and one-dimensional statistical parametric mapping assessed the effect of the interventions. Statistical significance was set at α = 0.05. Postintervention the isometric RT group revealed reduced peak KVM during early stance ( p = 0.04) while the dynamic RT group decreased peak KIRM ( p < 0.01) and KIRM over 8.8-86.6% ( p < 0.01) and 96.9-98.5% ( p = 0.047). An exploratory combined group analysis revealed reductions in KVM over 7.9-21.8% ( p = 0.002) and in KIRM over 8.3-90.5% ( p < 0.01) and 96.2-98.5% ( p = 0.046). Most lower limb isometric and dynamic strength measures increased after both resistance training interventions. Overall, both groups increased lower-body maximum strength while reducing kinetic knee joint variables associated with ACL injury risk during unplanned sidesteps. These results highlight the importance of increasing single-joint and multijoint strength in female athletes to mitigate the mechanical knee joint demands during sidestepping.

Exploring the biomechanics and fatigue patterns of eccentric quasi-isometric muscle actions in the knee extensors and flexors

PURPOSE

Eccentric quasi-isometric (EQI) resistance training is emerging as a promising option in sports medicine and rehabilitation. Despite prior research on EQI contractions in quadriceps and biceps brachii, their use in hamstring injury contexts is underexplored. Therefore, our study examines and contrasts the biomechanics and fatigue effects of EQI training on knee extensors and flexors.

METHODS

Following familiarization, 16 healthy, active participants (9 men, 7 women; 23.5 ± 2.6 years, 72.1 ± 12.8 kg, 173.4 ± 10.7 cm) performed, in random order, four EQI contractions for knee extensions and flexions, respectively. EQI contractions were isotonically loaded to 70% of concentric (60°·s-1) maximal voluntary contraction. Rest between repetitions was set at three minutes, while four minutes separated each muscle group. Peak torque, mean torque, and optimal angle were evaluated pre- and post-bouts. Inter-repetition contraction time and angular velocity were also assessed.

RESULTS

Average torque was 160.9 ± 44.2 and 71.5 ± 23.2 Nm for the extensors and flexors. Peak and mean torque significantly decreased for both extensors (p < 0.001, d = 0.70-0.71) and flexors (p ≤ 0.022, d = 0.36) after EQI contractions, respectively. However, the optimal angle increased for extensors (p < 0.001, d = 1.00) but not flexors (p = 0.811, d = 0.06). During EQI contractions, knee flexors exhibited greater intra-repetition velocity than extensors (p = 0.002; η2 = 0.50). Decreases in inter-repetition time and range of motion were more consistent for the extensors.

CONCLUSIONS

Distinct responses exist when comparing EQI contractions of the knee extensors and flexors, particularly their effect on peak torque angles. These findings suggest knee flexors may require lower relative intensities to align more closely with extensor EQI contractions.

Similar Regional Hypertrophy of the Elbow Flexor Muscles in Response to Low-Load Training With Vascular Occlusion at Short Versus Long Muscle Lengths

BACKGROUND

The regional hypertrophy response of elbow flexor muscles was compared after unilateral elbow flexion training in extended versus flexed shoulder position under vascular occlusion, which can induce muscle hypertrophy in the absence of muscle damage-induced edema/swelling.

HYPOTHESIS

Hypertrophy of elbow flexor muscles would be greater in extended compared with flexed shoulder position.

STUDY DESIGN

Randomized within-subject trial.

LEVEL OF EVIDENCE

Level 2.

METHODS

A total of 21 resistance-trained men (age, 25 ± 5 years; height, 1.78 ± 0.07 m; weight, 79.3 ± 13.1 kg) performed unilateral elbow flexions with one shoulder extended/elbow flexor muscles lengthened/long muscle length (LONG) and the other flexed/elbow flexor muscles shortened/short muscle length (SHORT) under a low-load (30% 1-repetition maximum) vascular occlusion training regimen (15 repetitions per set, 4 sets per session, 4 sessions per week for 3 weeks, using 80% of vascular occlusion pressure). Magnetic resonance imaging measured elbow flexor muscles cross-sectional area (EFCSA) pre- and post-training at 45%, 65%, and 85% of humerus length.

RESULTS

EFCSA significantly increased in both SHORT (P = 0.04) and LONG (P = 0.05) at 45% and 85% lengths (P < 0.01 for both). Changes in EFCSA between SHORT and LONG were statistically similar at the 45% (+6.20% vs +5.08%; Cohen d = 0.006; P = 0.98), 65% (+5.91% vs +3.83%, Cohen d = 0.28, P = 0.30), and 85% lengths (+8.51% vs +7.38%, Cohen d = 0.18,P = 0.56).

CONCLUSION

Muscle hypertrophy of the elbow flexor muscles displayed a similar behavior after low-load elbow flexion training with vascular occlusion performed in the extended versus flexed shoulder position.

CLINICAL RELEVANCE

Therapists, clinicians, and coaches may choose elbow flexion exercises expecting to achieve similar results for hypertrophy in this muscle group, such that exercise selection may rely on availability of equipment in the training room or personal preference.

Hamstrings Hypertrophy Is Specific to the Training Exercise: Nordic Hamstring versus Lengthened State Eccentric Training

INTRODUCTION

The hamstring muscles play a crucial role in sprint running but are also highly susceptible to strain injuries, particularly within the biceps femoris long head (BFlh). This study compared the adaptations in muscle size and strength of the knee flexors, as well as BFlh muscle and aponeurosis size, after two eccentrically focused knee flexion training regimes: Nordic hamstring training (NHT) vs lengthened state eccentric training (LSET, isoinertial weight stack resistance in an accentuated hip-flexed position) vs habitual activity (no training controls: CON).

METHODS

Forty-two healthy young males completed 34 sessions of NHT or LSET over 12 wk or served as CON ( n = 14/group). Magnetic resonance imaging-measured muscle volume of seven individual knee flexors and BFlh aponeurosis area, and maximum knee flexion torque during eccentric, concentric, and isometric contractions were assessed pre- and post-training.

RESULTS

LSET induced greater increases in hamstrings (+18% vs +11%) and BFlh (+19% vs +5%) muscle volumes and BFlh aponeurosis area (+9% vs +3%) than NHT (all P ≤ 0.001), with no changes after CON. There were distinctly different patterns of hypertrophy between the two training regimes, largely due to the functional role of the muscles; LSET was more effective for increasing the size of knee flexors that also extend the hip (2.2-fold vs NHT), whereas NHT increased the size of knee flexors that do not extend the hip (1.9-fold vs LSET; both P ≤ 0.001). Changes in maximum eccentric torque differed only between LSET and CON (+17% vs +4%; P = 0.009), with NHT (+11%) inbetween.

CONCLUSIONS

These results suggest that LSET is superior to NHT in inducing overall hamstrings and BFlh hypertrophy, potentially contributing to better sprint performance improvements and protection against hamstring strain injuries than NHT.

Acute effects of voluntary isometric contractions at maximal shortening vs. ballistic stretching on flexibility, strength and jump

Background

Isometric training is used in sport, conventional physical activity and rehabilitation. Understandably, there is a great deal of research related to its effect on performance. It is known that the length of the muscle at the moment of contraction is a determinant of strength levels. In the literature we find research on isometric training in short muscle lengths, although it has not been studied in maximally shortened positions or the acute effects that occur after its application. Ballistic stretching (BS) is also popular in sport. Their execution involves actively reaching maximally shortened muscle positions. So far, isometric training has not been compared with protocols involving ballistic stretching. Considering the above, the aim of the present study was to investigate the effects of BS and voluntary isometric contraction at maximal shortening (VICAMS) on range of motion, strength and vertical jump.

Methods

The study involved 60 healthy, physically active individuals (40 and 52 years old) who were randomly assigned to three groups: BS, VICAMS and a control group (CG). To assess acute effects, before and after the intervention, active range of motion (AROM), maximal voluntary isometric force (MVIF) and countermovement jump height (CMJ) were determined.

Results

Time main effects and time*group interactions were found for all variables (p < 0.001). Between-group differences were shown for the VICAMS group after the intervention, with statistically significant higher AROM values compared to the other groups. MVIF values were also higher in the VICAMS group. Intra-group differences were observed for the VICAMS and Ballistic groups, as values on all variables increased from baseline. For the CMJ, intra-group differences showed that both the VICAMS and BS groups improved values compared to baseline values.

Conclusions

The application of VICAMS induced acute improvements over BS in AROM, MVIF and CMJ. These results are important for coaches seeking immediate performance improvement and offer an optimal solution to the warm-up protocol.

Kinetic and kinematic profile of eccentric quasi-isometric loading

Eccentric quasi-isometric (EQI) contractions (maintaining a yielding contraction for as long as possible, beyond task failure) have gained interest in research and applied settings. However, little is known regarding the biomechanical profile of EQIs. Fourteen well-trained males performed four maximal effort knee-extensor EQIs, separated by 180 seconds. Angular impulse, velocity, and time-under-tension through the 30-100º range of motion (ROM), and in eight ROM brackets were quantified. Statistical parametric mapping, analyses of variance, and standardised effects (Hedges' g (ES), %Δ) detected between-contraction joint-angle-specific differences in time-normalised and absolute variables. Mean velocity was 1.34º·s-1 with most (62.5 ± 4.9%) of the angular impulse imparted between 40-70º. Most between-contraction changes occurred between 30-50º (p≤ 0.067, ES = 0.53 ± 0.31, 60 ± 52%), while measures remained constant between 50-100º (= 0.069-0.83, ES = 0.10 ± 0.26, 14.3 ± 24.6%). EQIs are a time-efficient means to impart high cumulative mechanical tension, especially at short to medium muscle lengths. However, angular impulse distribution shifts towards medium to long muscle lengths with repeat contractions. Practitioners may utilise EQIs to emphasize the initial portion of the ROM, and limit ROM, or apply EQIs in a fatigued state to emphasize longer muscle lengths.

Post-Activation Performance Enhancement of Punch Force and Neuromuscular Performance in Amateur Boxing: Toward a More Individualized and "Real-World" Approach

ABSTRACT

Finlay, MJ, Greig, M, Bridge, CA, and Page, RM. Post-activation performance enhancement of punch force and neuromuscular performance in amateur boxing: Toward a more individualized and "real-world" approach. J Strength Cond Res 38(6): 1063-1071, 2024-Previous research on post-activation performance enhancement has been applied in several sporting settings, although this is lacking in a boxing setting. This study explored the effectiveness of 2 upper-body conditioning activities in improving punch-specific performance during an amateur boxing-simulated bout. On 3 separate occasions, 10 male senior elite amateur boxers performed the following conditioning activities before a boxing-specific simulation protocol: isometric (ISO) punch, elastic resistance (ER) punch, and a control trial. Boxers performed maximal punches against a vertically mounted force plate, and countermovement jumps (CMJ) at baseline, before round 1, after each round, and 4 minutes after the simulation. Both conditioning activities, but not the control trial, produced small worthwhile increases (effect size ≥ 0.20; equal to or greater than the smallest worthwhile change) in punch force, although worthwhile increases in rate of force development were limited to the cross during the ISO trial. No group-based improvements in CMJ performance were observed. Individual analysis revealed that 6 boxers improved punch-specific performance to the greatest extent in the ISO trial; in contrast, only 1 boxer did so in the ER trial. Three boxers exhibited similar performance increases across trials. In conclusion, both conditioning activities may be applied to an amateur boxer's warm-up to acutely enhance punch-specific performance. The ISO conditioning activity seems most effective; however, the interindividual variability suggests a need for protocols to be individualized to each athlete. The conditioning activities in the present study may be applied to sparring, competitive bouts, or to other combat sports.

How to activate the glutes best? Peak muscle activity of acceleration-specific pre-activation and traditional strength training exercises

PURPOSE

Isometric training and pre-activation are proven to enhance acceleration performance. However, traditional strength training exercises do not mirror the acceleration-specific activation patterns of the gluteal muscles, characterized by ipsilateral hip extension during contralateral hip flexion. Therefore, the aim of the study was to determine gluteal muscle activity of acceleration-specific exercises compared to traditional strength training exercises.

METHODS

In a cross-sectional study design, the peak electromyographic activity of two acceleration-specific exercises was investigated and compared to two traditional strength training exercises each for the gluteus maximus and medius. Twenty-four participants from various athletic backgrounds (13 males, 11 females, 26 years, 178 cm, 77 kg) performed four gluteus maximus [half-kneeling glute squeeze (HKGS), resisted knee split (RKS), hip thrust (HT), split squat (SS)] and four gluteus medius [resisted prone hip abduction (RPHA), isometric clam (IC), side-plank with leg abduction (SP), resisted side-stepping (RSS)] exercises in a randomized order.

RESULTS

The RKS (p = 0.011, d = 0.96) and the HKGS (p = 0.064, d = 0.68) elicited higher peak gluteus maximus activity than the SS with large and moderate effects, respectively. No significant differences (p > 0.05) were found between the HT, RKS and HKGS. The RPHA elicited significantly higher gluteus medius activity with a large effect compared to RSS (p < 0.001, d = 1.41) and a moderate effect relative to the SP (p = 0.002, d = 0.78).

CONCLUSION

The acceleration-specific exercises effectively activate the gluteal muscles for pre-activation and strength training purposes and might help improve horizontal acceleration due to their direct coordinative transfer.

Reliability and Validity of the Strain Gauge "GSTRENGTH" for Measuring Peak Force in the Isometric Belt Squat at Different Joint Angles

Since isometric training is gaining popularity, some devices are being developed to test isometric force as an alternative to the more expensive force plates (FPs); thus, the aim of this study was to test the reliability and validity of "GSTRENGTH" for measuring PF in the isometric belt squat exercise. Five subjects performed 24 contractions at three different knee angles (90°, 105° and 120°) on two occasions (120 total cases). Peak force data were measured using FPs and a strain gauge (SG) and analyzed by Pearson's product-moment correlation coefficient, ICCs, Cronbach's alpha, a paired sample t-test and Bland-Altman plots. Perfect or almost perfect relationships (r: 0.999-1) were found with an almost perfect or perfect level of agreement (ICCs: 0.992-1; α: 0.998-1). The t-test showed significant differences for the raw data but not for the predictions by the equations obtained with the SG values. The Bland-Altman plots, when significant, showed trivial to moderate values for systematic bias in general. In conclusion, "GSTRENGTH" was shown to be a valid alternative to FPs for measuring PF.

Postsubmaximal Isometric Full Squat Jump Potentiation in Trained Men

ABSTRACT

Koźlenia, D, and Domaradzki, J. Postsubmaximal isometric full squat jump potentiation in trained men. J Strength Cond Res 38(3): 459-464, 2024-This study investigated the effects of postsubmaximal isometric full squats on jump height (JH). The study included 45 men aged 20-27 years with at least 6 years of resistance training experience that had been continuous for at least 2 years and a minimum relative strength of 120% of body mass in the full-back squat. They were randomly divided into an experimental group (EG) and a control group (CG). After a standard warm-up, subjects performed a countermovement jump (CMJ) to ascertain a baseline value. A conditioning activity (CA) introduced in the EG involved three 4-second sets of a high bar isometric full-back squat at 70% repetition maximum, with a 1-minute break. Five CMJs were performed in the following 9 minutes. Statistical significance was set at α = 0.05. A 2-way analysis of covariance (ANCOVA) (group-time), with baseline CMJ as a covariable, revealed statistically significant differences between groups ( p < 0.0001). The Bonferroni post hoc tests revealed higher results in the EG at the third, fifth, seventh, and ninth minutes ( p < 0.05). A 1-way repeated-measures analysis of variance (ANOVA) showed that time was statistically significant within groups ( p < 0.0001). The post hoc tests indicated JH improvement after 3 minutes compared with the baseline, and the trend persisted in the following 6 minutes ( p < 0.05) in the EG. The postactivation performance enhancement (PAPE) protocol based on a submaximal isometric full squat enhanced JH in the third minute after CA, which persisted for at least 6 minutes. These results indicate a requirement to evoke performance enhancement in response to an isometric CA.

Reliability of two devices for shoulder strength assessment: Wii Fit Balance Board and hand-held dynamometer

Background

The aim of this study was to compare the reliability and agreement between two devices - Wii Fit Balance Board (WBB) versus Hand-Held Dynamometer (HHD) to measure isometric strength during the athletic shoulder (ASH) test in healthy amateur rugby players.

Methods

Fifteen males (23.73 ± 2.8 years) completed two testing sessions. Maximal isometric contractions using the dominant arm (D) and non-dominant arm (ND) against a WBB and HHD were assessed at three angles of abduction (180°, 'I'; 135°, 'Y' and 90°, 'T'), in a prone lying position.

Results

The results indicate a very large correlation between the HHD and the WBB. WBB provides acceptable reliability at I-Test D (CV = 9.97%, ICC = 0.88) and HHD in the I-Test D (CV = 8.90%, ICC = 0.94), I-Test ND (CV = 8.60%, ICC = 0.95) in peak strength values. The HHD is most reliable in D ASH I-Y-T (CV = 10.94%) and WBB (CV = 11.05%). In the ND ASH I-Y-T test, the HHD is the most reliable (CV = 12.5%) compared to the WBB (CV = 14.43%).

Conclusions

These results suggest that WBB is a reliable device to assess strength in the ASH test with a very large correlation with the HHD. WBB and HHD are two affordable devices to assess isometric shoulder strength.

Effects of Resistance Training on Spasticity in People with Stroke: A Systematic Review

Resistance training induces neuromuscular adaptations and its impact on spasticity remains inadequately researched. This systematic review (PROSPERO: CRD42022322164) aimed to analyze the effects of resistance training, compared with no treatment, conventional therapy, or other therapies, in people with stroke-related spasticity. A comprehensive search was conducted up to October 2023 in PubMed, PEDro, Cochrane, Web of Science, and Scopus databases. Selection criteria were randomized controlled trials involving participants with stroke-related spasticity intervened with resistance training. The PEDro scale was used to evaluate the methodological quality. From a total of 274 articles, 23 full-text articles were assessed for eligibility and nine articles were included in the systematic review, involving 225 participants (155 males, 70 females; mean age: 59.4 years). Benefits were found to spasticity after resistance training. Furthermore, studies measuring spasticity also reported benefits to function, strength, gait, and balance. In conclusion, resistance training was superior to, or at least equal to, conventional therapy, other therapies, or no intervention for improving spasticity, as well as function, strength, gait, and balance. However, the results should be taken with caution because of the heterogeneity of the protocols used. Further research is needed to explore the effects of resistance training programs on people with stroke.

The effects of regional quadriceps architecture on angle-specific rapid force expression

Evaluating anatomical contributions to performance can increase understanding of muscle mechanics and guide physical preparation. While the impact of anatomy on muscular performance is well studied, the effects of regional quadriceps architecture on rapid torque or force expression are less clear. Regional (proximal, middle, and distal) quadriceps (vastus lateralis, rectus femoris, and vastus intermedius) thickness (MT), pennation angle (PA), and fascicle length (FL) of 24 males (48 limbs) were assessed via ultrasonography. Participants performed maximal isometric knee extensions at 40°, 70°, and 100° of knee flexion to evaluate rate of force development from 0 to 200 ms (RFD0-200). Measurements were repeated on three occasions with the greatest RFD0-200 and mean muscle architecture measures used for analysis. Linear regression models predicting angle-specific RFD0-200 from regional anatomy provided adjusted correlations (√adjR2) with bootstrapped compatibility limits. Mid-rectus femoris MT (√adjR2 = 0.41-0.51) and proximal vastus lateralis FL (√adjR2 = 0.42-0.48) were the best single predictors of RFD0-200, and the only measures to reach precision with 99% compatibility limits. Small simple correlations were found across all regions and joint angles between RFD0-200 and vastus lateralis MT (√adjR2 = 0.28 ± 0.13; mean ± SD), vastus lateralis FL (√adjR2 = 0.33 ± 0.10), rectus femoris MT (√adjR2 = 0.38 ± 0.10), and lateral vastus intermedius MT (√adjR2 = 0.24 ± 0.10). Between-correlation comparisons are reported within the article. Researchers should measure mid-region rectus femoris MT and vastus lateralis FL to efficiently and robustly evaluate potential anatomical contributions to rapid knee extension force changes, with distal and proximal measurements providing little additional value. However, correlations were generally small to moderate, suggesting that neurological factors may be critical in rapid force expression.

Effects of Low-Intensity Torque-Matched Isometric Training at Long and Short Muscle Lengths of the Hamstrings on Muscle Strength and Hypertrophy: A Randomized Controlled Study

ABSTRACT

Nakao, S, Ikezoe, T, Taniguchi, M, Motomura, Y, Hirono, T, Nojiri, S, Hayashi, R, Tanaka, H, and Ichihashi, N. Effects of low-intensity torque-matched isometric training at long and short muscle lengths of the hamstrings on muscle strength and hypertrophy: A randomized controlled study. J Strength Cond Res 37(10): 1978-1984, 2023-This study investigated the effects of low-intensity torque-matched isometric training on muscle hypertrophy and strengthening at long (LL) and short muscle lengths (SL). Twenty-eight young subjects completed an 8-week hamstring isometric training program (30% of maximal voluntary contraction (MVC) × 5 s × 20 repetitions × 5 sets × 3 times/week) at 30° knee flexion (LL) or 90° knee flexion (SL). The cross-sectional area (CSA) of the hamstrings and MVC were measured before and after the intervention. The active torque because of muscle contraction was calculated by subtracting the passive torque at rest from the total torque (30% MVC). The active torque was significantly lower in the LL training group than in the SL training group (p < 0.01), whereas there was no between-group difference in total torque during training. For CSA and MVC at 30° knee flexion, the split-plot analysis of variance (ANOVA) showed no significant time × group interaction; however, it did show a significant main effect of time (p < 0.05), indicating a significant increase after training intervention. As for MVC at 90° knee flexion, there was a significant time × group interaction (p < 0.05) and a significant simple main effect of time in both the LL (p < 0.01; Cohen's d effect size [ES] = 0.36) and SL (p < 0.01; ES = 0.64) training groups. Therefore, low-intensity isometric training at LL can induce hypertrophy and strengthening, even in cases where the active torque production is lower than that at SL, whereas the training at SL may be more effective for muscle strengthening at SL.

Effects of intrinsic foot muscle strengthening on the medial longitudinal arch mobility and function: A systematic review

OBJECTIVE

To Investigate the effects of intrinsic foot muscle (IFM) strengthening on foot's medial longitudinal arch (MLA) mobility and function in healthy individuals. We also identified exercise type and resistance training characteristics (series and repetitions).

METHODS

Eight databases were searched, between October 2020 and February 2021 and updated in May 2021. We included randomized controlled trials involving IFM strengthening exercises compared with controls (no exercise or exercises not involving isolated intrinsic foot muscle strengthening). Methodological quality of the studies was assessed using PEDro scale and Cochrane Risk of Bias tool. Quality of evidence was evaluated using GRADE model (Grading of Recommendations, Assessment, Development and Evaluations).

RESULTS

Four randomized controlled trials (RCT) were included. IFM strengthening did not change MLA mobility in the short-term (4 weeks); however, it promoted medium-term effects (8 weeks - low quality of evidence). IFM exercises improved function in the short and medium-term (low quality of evidence). Most studies used the short-foot exercise and the toe-towel curl exercise with contractions of 5 s and load progression from sitting to standing.

CONCLUSION

IFM strengthening exercises change MLA mobility in the medium-term (8 weeks) and improve the dynamic balance of healthy individuals in short- (4 weeks) and medium-terms.

The effectiveness of isometric protocols using an external load or voluntary effort on jump height enhancement in trained females

This study aimed to examine the effectiveness of isometric post-activation performance enhancement protocols using an external load (EXL) or voluntary effort (VE) on jump height (JH) in trained females divided into EXL (n = 15), VE (n = 14), and control (CON; n = 12) groups. JH was assessed using countermovement jumps at baseline and the third, fifth, seventh, and ninth minutes after the protocols. The EXL performed three sets of back squats with a 70%-repetition maximum load for four seconds, with one-minute breaks. The VE performed three sets of pushing against an immovable bar in the back squat position for five seconds, with one-minute breaks. The CON group ran on a treadmill at 6 km/h for four minutes. A RM-ANOVA showed a significant interaction for group-time (p < 0.01). The EXL protocol provided JH improvement at the third minute compared to baseline (p = 0.01), though it decreased in subsequent minutes (p < 0.05). JH declined in the VE group at the third and fifth minutes (p < 0.05), then peaked, surpassing baseline, after nine minutes (p = 0.04). No significant differences were found between the protocols in the relative effect (best-baseline) (p = 0.09), though the EXL group appeared to gain more (effect size [ES] = 0.76). Both protocols improved JH, but caution is required due to peak performance time and potential JH reduction.

Effect of free-weight vs. machine-based strength training on maximal strength, hypertrophy and jump performance - a systematic review and meta-analysis

BACKGROUND

The effectiveness of strength training with free-weight vs. machine equipment is heavily debated. Thus, the purpose of this meta-analysis was to summarize the data on the effect of free-weight versus machine-based strength training on maximal strength, jump height and hypertrophy.

METHODS

The review was conducted in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, and the systematic search of literature was conducted up to January 1st, 2023. Studies that directly compared free-weight vs. machine-based strength training for a minimum of 6 weeks in adults (18-60 yrs.) were included.

RESULTS

Thirteen studies (outcomes: maximal strength [n = 12], jump performance [n = 5], muscle hypertrophy [n = 5]) with a total sample of 1016 participants (789 men, 219 women) were included. Strength in free-weight tests increased significantly more with free-weight training than with machines (SMD: -0.210, CI: -0.391, -0.029, p = 0.023), while strength in machine-based tests tended to increase more with machine training than with free-weights (SMD: 0.291, CI: -0.017, 0.600, p = 0.064). However, no differences were found between modalities in direct comparison (free-weight strength vs. machine strength) for dynamic strength (SMD: 0.084, CI: -0.106, 0.273, p = 0.387), isometric strength (SMD: -0.079, CI: -0.432, 0.273, p = 0.660), countermovement jump (SMD: -0.209, CI: -0.597, 0.179, p = 0.290) and hypertrophy (SMD: -0.055, CI: -0.397, 0.287, p = 0.751).

CONCLUSION

No differences were detected in the direct comparison of strength, jump performance and muscle hypertrophy. Current body of evidence indicates that strength changes are specific to the training modality, and the choice between free-weights and machines are down to individual preferences and goals.

Effects of Different Isometric Training Programs on Muscle Size and Function in the Elbow Flexors

It remains unknown whether a regimen of a combination of high- and low-intensity resistance training increases muscle size and maximal voluntary isometric contraction (MVC) simultaneously. This study aimed to clarify the effect of the combination of high- and low-intensity resistance training on muscle size and neuromuscular function in the elbow flexors. Sixteen male adults participated in a 9-week isometric training regimen in elbow joint flexion of each arm. We randomly assigned two different training regimens to left and right arms: one aiming to strengthen maximal strength (ST) and the other aiming to develop muscle size as well as maximal strength, which consists of one contraction to volitional failure with 50% of MVC added to ST (COMB). Following the 3-week training to volitional failure as familiarization, the participants conducted the 6-week ST and COMB training in each arm. Before the intervention, and at the third (Mid) and ninth (Post) weeks, MVC and muscle thickness in the anterior part of the upper arm (ultrasound) were measured. Muscle cross-sectional area (mCSA) was derived from the obtained muscle thickness. From Mid to Post, the relative change in MVC was similar in both arms. The COMB regimen increased muscle size, but no significant change was found in ST. Following the 3-week isometric training to volitional failure, the 6-week training regimen for developing maximal voluntary and muscle hypertrophy increased MVC, with increasing mCSA, and the training-induced change in MVC was similar to that for developing maximal voluntary strength alone.

Six-Week Joint-Specific Isometric Strength Training Improves Serve Velocity in Young Tennis Players

PURPOSE

Evaluate the effects of 6 weeks of specific-joint isometric strength training on serve velocity (SV), serve accuracy (SA), and force-time curve variables.

METHODS

Sixteen young competition tennis players were divided into an intervention (n = 10) or control group (n = 6). SV, SA, maximal voluntary isometric contraction, peak rate of force development, rate of force development, and impulse (IMP) at different time frames while performing a shoulder internal rotation (SHIR) or flexion were tested at weeks 0, 3, and 6.

RESULTS

The intervention group showed significant increases in SV from pretest to posttest (7.0%, effect size [ES] = 0.87) and no variations in SA. Moreover, the intervention group showed significant increases from pretest to posttest in shoulder-flexion rate of force development at 150 (30.4%, ES = 2.44), 200 (36.5%, ES = 1.26), and 250 ms (43.7%, ES = 1.67) and in SHIR IMP at 150 (35.7%, ES = 1.18), 200 (33.4%, ES = 1.19), and 250 ms (35.6%, ES = 1.08). Furthermore, significant increases were found in shoulder-flexion rate of force development from intertest to posttest at 150 ms (24.5%, ES = 1.07) and in SHIR IMP at 150 (13.5%, ES = 0.90), 200 (19.1%, ES = 0.98), and 250 ms (27.2%, ES = 1.16). SHIR IMP changes from pretest to intertest were found at 150 ms (25.6%, ES = 1.04). The control group did not show changes in any of the tested variables.

CONCLUSIONS

Six weeks of upper-limb specific-joint isometric strength training alongside habitual technical-tactical workouts results in significant increases in SV without SA detriment in young tennis players.

Metabolic and cardiovascular responses to continuous and intermittent plank exercises

BACKGROUND

Plank exercise (PE) is a whole-body isometric muscle training which is beneficial for physical health. However, none of the previous studies investigated the responses within a typical isometric muscle training or PE protocol consisting of multiple sets. The application of PE was restricted for the understudied metabolic and cardiovascular responses, especially for the patients with cardiovascular diseases. This study is to alleviate the safety concerns of PE by investigating the PE-induced metabolic and cardiovascular responses.

METHODS

Eleven male recreational-level college students completed a baseline cardiopulmonary exercise test, continuous PE (CPE) and intermittent PE (IPE). Ratio of maximal oxygen uptake per kilogram of body mass (%VO_2max/kg), ratio of maximal heart rate (%HR_max), and respiratory exchange ratio (RER) were continuously measured during PEs and divided into seven equal timepoints. Blood pressure (BP) was measured every minute during, before, and after PEs. A mixed-model repeated measures ANOVA was used to examine the interaction effect of exercise × phase.

RESULTS

The %VO_2max/kg (F_6,69=11.25, P < 0.001), %HR_max (F_6,65=7.74, P < 0.001), RER (F_6,69=11.56, P < 0.001), and BP (systolic BP, F_2,26=8.42, P = 0.002; diastolic BP, F_2,24=22.63, P < 0.001) increased by safe magnitudes. Compared with the corresponding period in the IPE group, the %VO_2max/kg (33.5 [2.2] vs. 27.7 [1.9], P = 0.043) and %HR_max (63.2 [3.9] vs. 53.3 [2.1], P = 0.019) increased more significantly from the 40% duration of CPE. Systolic BP increased by larger magnitudes during CPE than IPE (154.2 [3.8] vs. 142.3 [4.8] mmHg, P = 0.002). RERs were over 1 during PEs without cardiovascular and metabolic variables over the anaerobic threshold.

CONCLUSION

Energy was mainly supplied by anaerobic metabolism during PEs. CPE may be preferable for trainees aiming at anaerobic capacity enhancement. IPEs may be preferable to CPEs for youth patients with mild and borderline cardiovascular diseases due to their lower metabolic and cardiovascular responses.

SPECIAL TRAINING ON LOWER LIMBS SMALL MUSCLE GROUPS STRENGTH

ABSTRACT Introduction Specific training with vibration can show short- and long-term effects on neuromuscular capacity. This training method gives muscles a frequent stimulus amplitude variation and can promote muscle strength, explosive power, neuromuscular coordination, and balance training. Objective This paper compares the effects of strength training with vibration on the strength of small muscle groups in the lower limbs of athletes. Methods 24 young people were randomly assigned to a low- and high-frequency group. Both groups used traditional strength training with the addition of 30 and 40Hz vibrational training. Training with load intensity between 30 and 70% of maximal strength lasting 60 minutes was repeated in 3 weekly sessions for eight weeks. Functional tests were recorded before and after the experiment, and their results were statistically analyzed. Results The peak torque of the hip muscles of the two groups of athletes increased significantly after training (P<0.05). In the high-frequency athletes, the peak in the hip extensor increased by 15.3% and the flexor by 18.2%; in the low-frequency group, there was an increase of 10.3%, representing a very significant difference (P<0.01). Conclusion Additional vibration stimulation for resistance strength training can effectively improve strength training. With a relatively small load, this training method can effectively improve maximal muscular strength, explosive power, and muscular endurance. Evidence level II; Therapeutic Studies - Investigating the results.

Postactivation Performance Enhancement of Amateur Boxers’ Punch Force and Neuromuscular Performance Following 2 Upper-Body Conditioning Activities

Purpose: The purpose of this study was to assess the efficacy of upper-body punch-specific isometric (ISO) and elastic resistance (ER) conditioning activities (CAs) on the punch force and neuromuscular performance of amateur boxers. Methods: Ten male senior elite amateur boxers (19.7 [1.2]| y; height 180.9 [7.0] cm; mass 78.7 [9.6] kg) visited the laboratory on 4 separate occasions. Initially, the participants performed baseline physical tests comprising bench-press 1-repetition maximum and countermovement jumps. On the other 3 occasions, the boxers performed maximal punches against a vertically mounted force plate and maximal countermovement jumps prior to and following an ISO or ER CA, as well as a control trial. Results: No interactions between CA × time were found in all performance variables. As observed by mean changes, effect sizes, and signal:noise ratio, both the ISO and ER, but not the control trial, consistently produced small to moderate, worthwhile increases in punch force and rate of force development, with the greatest increases in performance typically observed in the ISO trial. No meaningful improvements were observed in countermovement jump performance in all trials, indicative of a localized postactivation performance enhancement effect. Conclusion: In conclusion, the ISO and ER CAs may be implemented in an amateur boxers’ warm-up to acutely enhance punch-force variables, although the ISO punch appears to be the superior CA to improve punch-specific performance. The CAs used in the present study may also be relevant to other combat sports inclusive of a striking element.

Association between interindividual variability in training volume and strength gain

This study aimed to examine the association between interindividual variability in strength changes and in training volume. A total of 26 untrained men completed 4-weeks of isometric knee extension (KE group, n = 12) and hip flexion (HF group, n = 14) training. Each training session comprised four sets of ten isometric contractions, 3-s contractions every 20 s. Training volume, which was defined as impulse during contractions, and maximal voluntary contraction (MVC) torque during KE and HF were evaluated. Based on the magnitude of MVC torque changes, the participants were divided into the high and low responders (n = 13; KE = 6 and HF = 7 per responders). The MVC torque changes (KE, 20.8%; HF, 22.4%) and total training volume did not significantly differ between the two groups. A higher training volume was demonstrated in the low responders than the high responders. The total training volume was positively associated with the MVC torque changes in low responders (r = 0.869%, 95% confidence interval [0.610, 0.960], p < 0.001), but not in high responders [r = 0.229, 95% confidence interval (−0.368, 0.693), p = 0.451], KE or HF group. Results showed that training volume was an important factor in determining the magnitude of strength gains in low responders, and MVC torque could improve by approximately 20% with the use of the study protocol regardless of joint actions involved during training.

The relationship between handgrip and rotator cuff muscle strength in shoulder pain: a cross-sectional study

Background/Aims

Shoulder pain is reported to be the third most common musculoskeletal disorder. Rotator cuff muscles play an important role in stabilising the shoulder and decreasing pain. Assessment of handgrip strength has been proposed as an indicator of rotator cuff function in healthy individuals, but not in those experiencing shoulder pain. The aim of this study was to assess the relationship between handgrip strength and shoulder rotator cuff strength in patients experiencing shoulder pain as a result of pathology or surgical intervention. A secondary aim was to identify any association between the duration of shoulder pain and handgrip strength and shoulder rotator cuff strength.

Methods

A total of 32 patients with shoulder pain (19 men, 13 women) were evaluated. The mean age was 52.88 (± 15.66) years, with a mean duration of shoulder pain of 13.44 (± 10.22) weeks. Handgrip strength was measured using the standard Jamar hydraulic hand dynamometer, and individual isometric rotator cuff strength was measured using the Baseline push-pull dynamometer.

Results

Correlation was found between handgrip strength and the abductor (r=0.58), external rotator (r=0.57), and internal rotator strength (r=0.59). A linear regression model was used to derive the equations for the association. No significant (P>0.05) correlation was found between the duration of pain and the handgrip strength or rotator cuff strength.

Conclusions

The strength of the correlation found indicates that handgrip strength can be used for assessment and within a rehabilitation programme to monitor rotator cuff function in patients with shoulder pain or post-surgical rehabilitation. The strength of rotator cuff muscles can be predicted by the equations derived from the regression model relating to grip strength assessment.

Appropriate Reporting of Exercise Variables in Resistance Training Protocols: Much more than Load and Number of Repetitions

Manipulating resistance training variables is crucial to plan the induced stimuli correctly. When reporting the exercise variables in resistance training protocols, sports scientists and practitioners often refer to the load lifted and the total number of repetitions. The present conceptual review explores all within-exercise variables that may influence the strength and hypertrophic gains, and the changes in muscle architecture. Together with the (1) load and (2) the number of repetitions, (3) performing repetitions to failure or not to failure, (4) the displacement of the load or the range of movement (full or partial), (5) the portion of the partial movement to identify the muscle length at which the exercise is performed, (6) the total time under tension, the duration of each phase and the position of the two isometric phases, (7) whether the concentric, eccentric or concentric-eccentric phase is performed, (8) the use of internal or external focus and (9) the inter-set rest may all have repercussions on the adaptations induced by each resistance exercise. Manipulating one or more variable allows to increase, equalize or decrease the stimuli related to each exercise. Sports scientists and practitioners are invited to list all aforementioned variables for each exercise when reporting resistance training protocols.

Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position

The biarticular triceps brachii long head (TB_Long) is lengthened more in the overhead than neutral arm position. We compared triceps brachii hypertrophy after elbow extension training performed in the overhead vs. neutral arm position. Using a cable machine, 21 adults (14 males and 7 females, age: 23.4 ± 1.6 y, height: 1.69 ± 0.09 m, body mass: 64.5 ± 12.4 kg) conducted elbow extensions (90-0°) with one arm in the overhead (Overhead-Arm) and the other arm in the neutral (Neutral-Arm) position at 70% one-repetition maximum (1RM), 10 reps/set, 5 sets/session, 2 sessions/week for 12 weeks. Training load was gradually increased (+5% 1RM/session) when the preceding session was completed without repetition failure. 1RM of the assigned condition and MRI-measured muscle volume of the TB_Long, monoarticular lateral and medial heads (TB_Lat+Med), and whole triceps brachii (Whole-TB) were assessed pre- and post-training. Training load and 1RM increased in both arms similarly (+62-71% at post, P = 0.285), while their absolute values/weights were always lower in Overhead-Arm (-34-39%, P < 0.001). Changes in muscle volume in Overhead-Arm compared to Neutral-Arm were 1.5-fold greater for the TB_Long (+28.5% vs. +19.6%, Cohen's d = 1.272, P < 0.001), 1.4-fold greater for the TB_Lat+Med (+14.6% vs. +10.5%, d = 1.106, P = 0.002), and 1.4-fold greater for the Whole-TB (+19.9% vs. +13.9%, d = 1.427, P < 0.001). In conclusion, triceps brachii hypertrophy was substantially greater after elbow extension training performed in the overhead versus neutral arm position, even with lower absolute loads used during the training.

Isotonic and Isometric Exercise Interventions Improve the Hamstring Muscles’ Strength and Flexibility: A Narrative Review

Background: Hamstring weakness has been associated with an increased risk of hamstring strain, a common sports injury that occurs when athletes perform actions such as quick sprints. The hamstring complex comprises three distinct muscles: the long and short heads of the bicep femoris, the semimembranosus, and the semitendinosus. Methods: The researchers collected the data from different electronic databases: PubMed, Google Scholar, and the Web of Science. Results: Many studies have been conducted on the numerous benefits of hamstring strength, in terms of athletic performance and injury prevention. Isotonic and isometric exercises are commonly used to improve hamstring strength, with each exercise type having a unique effect on the hamstring muscles. Isotonic exercise improves the muscles’ strength, increasing their ability to resist any force, while isometric training increases strength and the muscles’ ability to produce power by changing the muscle length. Conclusions: These exercises, when performed at low intensity, but with high repetition, can be used by the healthy general population to prepare for training and daily exercise. This can improve hamstring muscle strength and flexibility, leading to enhanced performance and reduced injury risk.

The Effect of Yoga on Health-Related Fitness among Patients with Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis

BACKGROUND

There is a need for a type of physical activity that could address the challenging cycle of physical inactivity, impaired health-related fitness, and type 2 diabetes mellitus (T2DM) conditions. Yoga could be one type of exercise to overcome the barriers to adhere to regular physical activity. The current study aimed to systematically review the effect of yoga on health-related fitness, including cardiorespiratory fitness, muscle strength, body composition, balance, and flexibility, among patients with T2DM.

METHODS

We systematically searched four databases and two registries (Pubmed, Scopus, Cochrane, Embase, WHO-ITCRP, and Clinicaltrials.gov) in September 2021, following a registered protocol on PROSPERO (CRD42022276225). Study inclusion criteria were T2DM patients with or without complication, yoga intervention as a single component or as a complement compared to other kinds of exercise or an inactive control, health-related fitness, and a randomized, controlled trial or quasi-experimental with control group design. The ROBINS-I tool and ROB 2.0 tool were used to assess the risk of bias in the included studies. A vote-counting analysis and meta-analysis computed using random effects' models were conducted.

RESULTS

A total of 10 records from 3 quasi-experimental and 7 randomized, controlled trials with 815 participants in total were included. The meta-analysis favored yoga groups compared to inactive controls in improving muscle strength by 3.42 (95% confidence interval 2.42 to 4.43), repetitions of chair stand test, and improving cardiorespiratory fitness by 6.6% (95% confidence interval 0.4 to 12.8) improvement of baseline forced vital capacity. The quality of evidence for both outcomes was low.

CONCLUSION

Low-quality evidence favored yoga in improving health-related fitness, particularly muscle strength and cardiorespiratory fitness, among patients with T2DM.

FUNDING

All authors in this systematic review received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Effects of Performing Isometric Bench Press Training at Single Versus Multiple Joint Positions on Strength and Power Performance

Isometric strength training has been reported to benefit various sport-related dynamic performances. However, it is still unknown whether performing isometric strength training at single or multiple joint angles would elicit greater benefit.

PURPOSE

To compare the effects of isometric bench press performed at single (SIBP) and multiple (MIBP) joint angles on dynamic strength and overhead throwing performance.

METHODS

Sixteen male softball and baseball athletes performed overhead throwing, 1-repetition-maximum (1RM) bench press, and ballistic push-up during pretest and posttest. They were then randomly assigned to either SIBP or MIBP to undergo 12 strength training sessions. During the training, isometric bench press was performed at only 90° elbow angle for SIBP but at 60°, 90°, and 120° elbow angles for MIBP.

RESULTS

A significant main time effect was observed for bench press 1RM (P = .003) and relative 1RM (P < .001). Similarly, a significant main time effect was observed for ballistic push-up peak power only (P = .037). There was no significant change in overhead throwing velocity in either group. There was also no significant difference in change in all measures between groups. However, a moderate effect in favor of MIBP was observed for change in ballistic push-up peak power (P = .180, g = 0.67).

CONCLUSIONS

Based on the current findings, the inclusion of both SIBP and MIBP were equally beneficial to maximal strength development. However, performing MIBP had a greater effect on power development.

Immediate and cumulative effects of upper-body isometric exercise on the cornea and anterior segment of the human eye

Objectives

The execution of isometric resistance training has demonstrated to cause changes in the ocular physiology. The morphology of the cornea and anterior chamber is of paramount importance in the prevention and management of several ocular diseases, and thus, understating the impact of performing isometric exercise on the eye physiology may allow a better management of these ocular conditions. We aimed to determine the short-term effects of 2-minutes upper-body isometric effort at two different intensities on corneal and anterior eye morphology.

Methods

Eighteen healthy young adults performed a 2-minutes isometric biceps-curl exercise against two loads relative to their maximum strength capacity (high-intensity and low-intensity) in a randomized manner. An Oculus Pentacam was used to measure the corneal morphology and anterior chamber parameters in both experimental conditions at baseline, during the isometric effort (after 30, 60, 90 and 120 seconds), and after 30 and 120 seconds of passive recovery.

Results

We found that isometric effort causes an increase in pupil size (P < 0.001), and a decrease in the iridocorneal angle (P = 0.005), anterior chamber volume (P < 0.001) and K-flat (P < 0.001) during isometric effort, with these effects being more accentuated in high-intensity condition (P < 0.005 in all cases).Performing 2-minutes upper-body isometric effort did not alter anterior chamber depth, central corneal thickness, corneal volume, and K-steep (P > 0.05 in all cases).

Conclusions

Our data exhibit that performing 2-minutes of upper-body isometric exercise modifies several parameters of the corneal morphology and anterior eye biometrics, with these changes being greater for the high-intensity exercise condition. The findings of this study may be of relevance for the prevention and management of corneal ectasias and glaucoma.

Effects of compression garment on muscular efficacy, proprioception, and recovery after exercise-induced muscle fatigue onset for people who exercise regularly

Fatigue is a major cause of exercise-induced muscle damage (EIMD). Compression garments (CGs) can aid post-exercise recovery, therefore, this study explored the effects of CGs on muscular efficacy, proprioception, and recovery after exercise-induced muscle fatigue in people who exercise regularly. Twelve healthy participants who exercised regularly were enrolled in this study. Each participant completed an exercise-induced muscle fatigue test while wearing a randomly assigned lower-body CG or sports pants (SP); after at least 7 days, the participant repeated the test while wearing the other garment. The dependent variables were muscle efficacy, proprioception (displacements of center of pressure/COP, and absolute error), and fatigue recovery (muscle oxygen saturation/SmO2, deoxygenation and reoxygenation rate, and subjective muscle soreness). A two-way repeated measure analysis of variance was conducted to determine the effect of garment type. The results indicated that relative to SP use, CG use can promote muscle efficacy, proprioception in ML displacement of COP, and fatigue recovery. Higher deoxygenation and reoxygenation rates were observed with CG use than with SP use. For CG use, SmO2 quickly returned to baseline value after 10 min of rest and was maintained at a high level until after 1 h of rest, whereas for SP use, SmO2 increased with time after fatigue onset. ML displacement of COP quickly returned to baseline value after 10 min of rest and subsequently decreased until after 1 hour of rest. Relative to SP use, CG use was associated with a significantly lower ML displacement after 20 min of rest. In conclusion, proprioception and SmO2 recovery was achieved after 10 min of rest; however, at least 24 h may be required for recovery pertaining to muscle efficacy and soreness regardless of CG or SP use.

Putting "Heavy" into Heavy Slow Resistance

The body of literature on tendinopathy management has come a long way in the last few decades and a variety of changes in the clinical approach have emerged from this research. One particular approach that shows promise has been called "heavy slow resistance" (HSR), and this has been the subject of investigation in a number of randomized controlled trials. While the premise for this approach is defensible, a critical examination of the implementation of these HSR protocols results in some concerns when compared to basic exercise science principles. This article lays out some considerations that will help future investigators to improve their exercise prescription approaches in this area.