How long does the protective effect on eccentric exercise-induced muscle damage last?

Biomarkers in Endurance Exercise: Individualized Regulation and Predictive Value

The high interindividual variability of exercise response complicates the efficient use of blood-based biomarkers in sports. To address this problem, a useful algorithm to characterize the individual regulation and predictive value of different candidate markers will be developed. Forty-nine participants completed two identical exercise trials. Blood samples were collected before, immediately after, 3 hours after, and 24 hours after completion of exercise. Plasma concentrations of interleukin (IL-) 1RA, IL-6, IL-8, IL-10, IL-15, creatine kinase (CK), cortisol, c-reactive protein (CRP), lactate dehydrogenase (LDH), and thiobarbituric acid reactive substances (TBARS) were measured. Individualized regulation was analyzed using k-means clustering and a Group Assignment Quality (GAQ) score. Regression trees with a bootstrapped-aggregated approach were used to assess the predictive qualities of the markers. For most of the markers studied, a distinction can be made between individuals who show a stronger or weaker response to a particular endurance training program. The regulation of IL-6, IL-8, IL-10, and CK exhibited a high degree of stability within the individuals. Regarding the predictive power of the markers, for all dependent variables, the most accurate predictions were obtained for cortisol and IL-8 based on the baseline value. For CK, a good prediction of recovery of maximal strength and subjective feeling of exhaustion can be made. For IL-1RA and TBARS, especially their reregulation can be predicted if the baseline level is known. Focusing individual variations in biomarker responses, our results suggest the combined use of IL-6, IL-8, IL-10, and CK for the personalized management of stress and recovery cycles following endurance exercise.

Grass-Fed and Non-Grass-Fed Whey Protein Consumption Do Not Attenuate Exercise-Induced Muscle Damage and Soreness in Resistance-Trained Individuals: A Randomized, Placebo-Controlled Trial

Eccentric muscle contractions can cause structural damage to muscle cells resulting in temporarily decreased muscle force production and soreness. Prior work indicates pasture-raised dairy products from grass-fed cows have greater anti-inflammatory and antioxidant properties compared to grain-fed counterparts. However, limited research has evaluated the utility of whey protein from pasture-raised, grass-fed cows to enhance recovery compared to whey protein from non-grass-fed cows. Therefore, using a randomized, placebo-controlled design, we compared the effect of whey protein from pasture-raised, grass-fed cows (PRWP) to conventional whey protein (CWP) supplementation on indirect markers of muscle damage in response to eccentric exercise-induced muscle damage (EIMD) in resistance-trained individuals. Thirty-nine subjects (PRWP, n = 14; CWP, n = 12) completed an eccentric squat protocol to induce EIMD with measurements performed at 24, 48, and 72 h of recovery. Dependent variables included: delayed onset muscle soreness (DOMS), urinary titin, maximal isometric voluntary contraction (MIVC), potentiated quadriceps twitch force, countermovement jump (CMJ), and barbell back squat velocity (BBSV). Between-condition comparisons did not reveal any significant differences (p ≤ 0.05) in markers of EIMD via DOMS, urinary titin, MIVC, potentiated quadriceps twitch force, CMJ, or BBSV. In conclusion, neither PRWP nor CWP attenuate indirect markers of muscle damage and soreness following eccentric exercise in resistance-trained individuals.

Adaptability to eccentric exercise training is diminished with age in female mice

The ability of skeletal muscle to adapt to eccentric contractions has been suggested to be blunted in older muscle. If eccentric exercise is to be a safe and efficient training mode for older adults, preclinical studies need to establish if older muscle can effectively adapt and if not, determine the molecular signatures that are causing this impairment. The purpose of this study was to quantify the extent age impacts functional adaptations of muscle and identify genetic signatures associated with adaptation (or lack thereof). The anterior crural muscles of young (4 mo) and older (28 mo) female mice performed repeated bouts of eccentric contractions in vivo (50 contractions/wk for 5 wk) and isometric torque was measured across the initial and final bouts. Transcriptomics was completed by RNA-sequencing 1 wk following the fifth bout to identify common and differentially regulated genes. When torques post eccentric contractions were compared after the first and fifth bouts, young muscle exhibited a robust ability to adapt, increasing isometric torque 20%-36%, whereas isometric torque of older muscle decreased up to 18% (P ≤ 0.047). Using differential gene expression, young and older muscles shared some common transcriptional changes in response to eccentric exercise training, whereas other transcripts appeared to be age dependent. That is, the ability to express particular genes after repeated bouts of eccentric contractions was not the same between ages. These molecular signatures may reveal, in part, why older muscles do not appear to be as adaptive to exercise training as young muscles.NEW & NOTEWORTHY The ability to adapt to exercise training may help prevent and combat sarcopenia. Here, we demonstrate young mouse muscles get stronger whereas older mouse muscles become weaker after repeated bouts of eccentric contractions, and that numerous genes were differentially expressed between age groups following training. These results highlight that molecular and functional plasticity is not fixed in skeletal muscle with advancing age, and the ability to handle or cope with physical stress may be impaired.

The acute and repeated bout effects of multi-joint eccentric exercise on physical function and balance in older adults

PURPOSE

Eccentric muscle actions generate high levels of force at a low metabolic cost, making them a suitable training modality to combat age-related neuromuscular decline. The temporary muscle soreness associated with high intensity eccentric contractions may explain their limited use in clinical exercise prescription, however any discomfort is often alleviated after the initial bout (repeated bout effect). Therefore, the aims of the present study were to examine the acute and repeated bout effects of eccentric contractions on neuromuscular factors associated with the risk of falling in older adults.

METHODS

Balance, functional ability [timed up-and-go and sit-to-stand], and lower-limb maximal and explosive strength were measured in 13 participants (67.6 ± 4.9 year) pre- and post-eccentric exercise (0, 24, 48, and 72 hr) in Bout 1 and 14 days later in Bout 2. The eccentric exercise intervention was performed on an isokinetic unilateral stepper ergometer at 50% of maximal eccentric strength at 18 step‧min-1 per limb for 7 min (126 steps per limb). Two-way repeated measures ANOVAs were conducted to identify any significant effects (P ≤ 0.05).

RESULTS

Eccentric strength significantly decreased (- 13%) in Bout 1 at 24 hr post-exercise; no significant reduction was observed at any other time-point after Bout 1. No significant reductions occurred in static balance or functional ability at any time-point in either bout.

CONCLUSION

Submaximal multi-joint eccentric exercise results in minimal disruption to neuromuscular function associated with falls in older adults after the initial bout.

Sensory, functional and electromyographic variables show different recovery patterns over a seven day period following exercise-induced pain in the hamstrings

BACKGROUND

Delayed-onset muscle soreness (DOMS) is common after unaccustomed exercises and can restrict performance if intense physical activities are performed while the muscle is still sore. This study aimed to evaluate the recovery process following exercise-induced DOMS over a seven-day period by evaluating sensory, functional, and electromyographic parameters.

METHODS

Twenty-four healthy males participated in four experimental sessions (Day-0, Day-2, Day-4, Day-7). Pain perception, pressure pain sensitivity, active range of motion, maximal isometric strength, and muscle activity of the hamstrings during the maximal isometric contraction were assessed bilaterally at each session. A single-leg deadlift eccentric exercise (5-sets of 20-reps) was performed at the end of Day-0 to induce DOMS in the dominant leg.

FINDINGS

At Day-2, the DOMS-side showed increased pain sensitivity and decreased active range of motion, strength and muscle activity compared to Day-0 (P < 0.015). Muscle activity on the DOMS-side reached similar values than at baseline on Day-4, whereas pain perception, pressure pain sensitivity, maximal isometric strength, and active range of motion had returned to the baseline state on Day-7. No changes over time were observed on the control-side, showing all variables an excellent reliability between values at Day-0 and Day-7 (Intraclass Correlation Coefficient > 0.90).

INTERPRETATION

Surface electromyographic values during a maximal isometric contraction recover faster than the other parameters. Given the heterogeneous path of altered variables towards DOMS recovery, trainers and clinicians should consider a multimodal assessment, including quantitative sensory and functional measures in addition to the subjective perception of recovery.

The Effects of Pre-conditioning on Exercise-Induced Muscle Damage: A Systematic Review and Meta-analysis

BACKGROUND

Several studies have utilised isometric, eccentric and downhill walking pre-conditioning as a strategy for alleviating the signs and symptoms of exercise-induced muscle damage (EIMD) following a bout of damaging physical activity.

OBJECTIVES

This systematic review and meta-analysis examined the effects of pre-conditioning strategies on indices of muscle damage and physical performance measures following a second bout of strenuous physical activity.

DATA SOURCES

PubMed, CINAHL and Scopus.

ELIGIBILITY CRITERIA

Studies meeting the PICO (population, intervention/exposure, comparison, and outcome) criteria were included in this review: (1) general population or "untrained" participants with no contraindications affecting physical performance; (2) studies with a parallel design to examine the prevention and severity of muscle-damaging contractions; (3) outcome measures were compared using baseline and post-intervention measures; and (4) outcome measures included any markers of indirect muscle damage and muscular contractility measures.

PARTICIPANTS

Individuals with no resistance training experiences in the previous 6 or more months.

INTERVENTIONS

A single bout of pre-conditioning exercises consisting of eccentric or isometric contractions performed a minimum of 24 h prior to a bout of damaging physical activity were compared to control interventions that did not perform pre-conditioning prior to damaging physical activity.

STUDY APPRAISAL

Kmet appraisal system.

SYNTHESIS METHODS

Quantitative analysis was conducted using forest plots to examine standardised mean differences (SMD, i.e. effect size), test statistics for statistical significance (i.e. Z-values) and between-study heterogeneity by inspecting I2.

RESULTS

Following abstract and full-text screening, 23 articles were included in this paper. Based on the meta-analysis, the pre-conditioning group exhibited lower levels of creatine kinase at 24 h (SMD =  - 1.64; Z = 8.39; p = 0.00001), 48 h (SMD =  - 2.65; Z = 7.78; p = 0.00001), 72 h (SMD =  - 2.39; Z = 5.71; p = 0.00001) and 96 h post-exercise (SMD =  - 3.52; Z = 7.39; p = 0.00001) than the control group. Delayed-onset muscle soreness was also lower for the pre-conditioning group at 24 h (SMD =  - 1.89; Z = 6.17; p = 0.00001), 48 h (SMD =  - 2.50; Z = 7.99; p = 0.00001), 72 h (SMD =  - 2.73; Z = 7.86; p = 0.00001) and 96 h post-exercise (SMD =  - 3.30; Z = 8.47; p = 0.00001). Maximal voluntary contraction force was maintained and returned to normal sooner in the pre-conditioning group than in the control group, 24 h (SMD = 1.46; Z = 5.49; p = 0.00001), 48 h (SMD = 1.59; Z = 6.04; p = 0.00001), 72 h (SMD = 2.02; Z = 6.09; p = 0.00001) and 96 h post-exercise (SMD = 2.16; Z = 5.69; p = 0.00001). Range of motion was better maintained by the pre-conditioning group compared with the control group at 24 h (SMD = 1.48; Z = 4.30; p = 0.00001), 48 h (SMD = 2.20; Z = 5.64; p = 0.00001), 72 h (SMD = 2.66; Z = 5.42; p = 0.00001) and 96 h post-exercise (SMD = 2.5; Z = 5.46; p = 0.00001). Based on qualitative analyses, pre-conditioning activities were more effective when performed at 2-4 days before the muscle-damaging protocol compared with immediately prior to the muscle-damaging protocol, or 1-3 weeks prior to the muscle-damaging protocol. Furthermore, pre-conditioning activities performed using eccentric contractions over isometric contractions, with higher volumes, greater intensity and more lengthened muscle contractions provided greater protection from EIMD.

LIMITATIONS

Several outcome measures showed high inter-study heterogeneity. The inability to account for differences in durations between pre-conditioning and the second bout of damaging physical activity was also limiting.

CONCLUSIONS

Pre-conditioning significantly reduced the severity of creatine kinase release, delayed-onset muscle soreness, loss of maximal voluntary contraction force and the range of motion decrease. Pre-conditioning may prevent severe EIMD and accelerate recovery of muscle force generation capacity.

The Contralateral Repeated Bout Effect of Elbow Flexors Is Not Observed in Young Women Following Mild Muscle Damage from Eccentric Exercises

Investigation of the contralateral repeated bout effect (CL-RBE) in women is scarce. Therefore, this study aimed at examining whether CL-RBE exists in women. Twelve healthy women (age: 20.9 ± 2.5 years) performed two bouts of maximal elbow flexor eccentric exercise (3 sets × 15 repetitions per bout) separated by 14 days, using the opposite arms. Surface Electromyography (EMG) was recorded during both exercise bouts. The isokinetic muscle strength (60°/s), muscle soreness, range of motion (ROM), limb girth, and blood creatine kinase activity were measured pre-exercise, and at 24 and 48 h post-exercise with the muscle strength being measured immediately post-exercise as well. Significant main effects of time were observed for muscle strength, muscle soreness and ROM (p < 0.05). There were no significant differences between bouts for all the measured variables including the EMG median frequency (p > 0.05). These results suggest that the CL-RBE of elbow flexors was not evident in young healthy women. This was because the mild muscle damage induced by the initial bout of exercise was either not enough to initiate the CL-RBE or the CL-RBE in women lasted shorter than two weeks. This study provides important information for future studies on CL-RBE in women.

Neuromuscular fatigue and muscle damage following a simulated singles badminton match

PURPOSE

To understand muscle damage in badminton, changes in neuromuscular function were investigated after simulated badminton singles matches performed by ten state-level male players.

METHODS

Each participant played eight matches and measurements were taken before, immediately after, and 1 and 24 h after each match. Maximal voluntary isometric contraction (MVC) torque of the knee extensors and flexors, voluntary activation (VA) during MVC and torques generated by doublet (T_Doublet), 20 (T₂₀) and 80 Hz (T₈₀) electrical stimulations of the knee extensors were measured from the dominant leg (the racket-hold arm side). Muscle soreness was assessed by a 100-mm visual analogue scale from both legs. The number of lunges performed by each participant in each match was analysed by videos, and its relations to other measures were examined.

RESULTS

Pre-match knee extensor and flexor MVC torques were 278.4 ± 50.8 Nm and 143.0 ± 36.2 Nm, respectively. Knee extensor MVC torque of the dominant leg decreased immediately (12.0 ± 2.9%) and 1 h post-match (16.0 ± 3.2%), but returned to baseline at 24 h post-match. VA (11.4 ± 2.9%), T_Doublet (13.1 ± 6.0%), T₂₀ (31.1 ± 12.3%) and T₈₀ (25.5 ± 7.9%) decreased (p < 0.01) immediately post-match but recovered by 24 h post-match. A significant correlation (r = - 0.64, p < 0.01) was observed between the total number of lunges performed in a match (160-240 times) and the magnitude of decrease in MVC torque (6.4-14.7%). Muscle soreness developed more (p < 0.05) for the dominant (51.5 ± 11.6 mm) than the non-dominant leg (18.8 ± 8.6 mm).

CONCLUSION

Muscle damage induced by singles badminton matches was minimal, but the more the lunges are performed, the greater the neuromuscular fatigue.

Exercise induced muscle damage and repeated bout effect: an update for last 10 years and future perspectives

Exercise-induced muscle damage (EIMD) and repeated bout effect (RBE) are widely researched across various populations. EIMD is the muscle damage occurring after one bout of unaccustomed exercise while RBE is the attenuation of the same muscle damage in subsequent second bout. RBE seems to have significant implications for exercise prescription. Despite existence of vast literature, there is lack of clarity on the effects of EIMD and RBE in a healthy population. The purpose of this study is to review the literature on EIMD and RBE in healthy participants published during the last 10 years. The search of major databases (including Scopus, Google Scholar and PubMed) was conducted using specific keywords ‘Exercise induced muscle damage’, ‘Repeated bout effect’, ‘Healthy participants’ ‘Pre-conditioning’, ‘Eccentric exercise’. Studies published from 2011 onwards which included EIMD and RBE assessment in healthy participants were included in this review. Database searching revealed a total of 38 studies on EIMD and RBE in healthy participants. Three major themes of papers were identified that focused on EIMD and RBE along with (1) age related differences, (2) sex-based differences, and (3) response in athletes. Findings of this comprehensive review suggests that both EIMD and RBE are age, and sex specific. Delayed onset muscle soreness played a major role in both EIMD and RBE in all the population types. Female participants are less susceptible to EIMD as compared to age-matched male counterparts. Moreover, both EIMD and RBE are more elicited in middle aged and younger adults as compared to children and older adults while the magnitude of RBE turns out to be minimal in trained individuals due to persisting adaptations.

Including the Eccentric Phase in Resistance Training to Counteract the Effects of Detraining in Women: A Randomized Controlled Trial

ABSTRACT

Coratella, G, Beato, M, Bertinato, L, Milanese, C, Venturelli, M, and Schena, F. Including the eccentric phase in resistance training to counteract the effects of detraining in women: a randomized controlled trial. J Strength Cond Res 36(11): 3023-3031, 2022-The current study compared the effects of concentric-based (CONC), eccentric-based (ECC), and traditional concentric-eccentric (TRAD) resistance training on muscle strength, mass, and architecture and the postdetraining retention of the training-induced effects in women. Sixty women were randomly assigned to unilateral volume-equated CONC, ECC, or TRAD knee extension training or control ( N = 15 per group). Before training, after an 8-week intervention period, and after an 8-week detraining period, isokinetic concentric, eccentric, and isometric torque were measured. In addition, thigh lean mass was assessed by dual X-ray absorptiometry and vastus lateralis thickness, pennation angle, and fascicle length by ultrasound. After training, concentric and isometric torque increased ( p < 0.05) similarly in all groups, whereas eccentric torque increased more in ECC than that in CONC (+13.1%, effect size (ES): 0.71 [0.04-1.38]) and TRAD (+12.6%, ES: 0.60 [0.12-1.08]). Thigh lean mass increased in ECC (+6.1%, ES: 0.47 [0.27-0.67]) and TRAD (+3.1%, ES: 0.33 [0.01-0.65]). Vastus lateralis thickness and pennation angle increased ( p < 0.05) similarly in all groups, whereas fascicle elongation was visible in ECC (+9.7%, ES: 0.92 [0.14-1.65]) and TRAD (+7.1%, ES: 0.64 [0.03-1.25]). After detraining, all groups retained ( p < 0.05) similar concentric torque. ECC and TRAD preserved eccentric torque ( p < 0.05), but ECC more than TRAD (+17.9%, ES: 0.61 [0.21-1.21]). All groups preserved isometric torque ( p < 0.05), but ECC more than CONC (+14.2%, ES: 0.71 [0.04-1.38]) and TRAD (+13.8%, ES: 0.65 [0.10-1.20]). Thigh lean mass and vastus lateralis fascicle length were retained only in ECC ( p < 0.05), pennation angle was preserved in all groups ( p < 0.05), and thickness was retained in CONC and ECC ( p < 0.05). Including the eccentric phase in resistance training is essential to preserve adaptations after detraining.

Psoriasis, Is It a Microdamage of Our "Sixth Sense"? A Neurocentric View

Psoriasis is considered a multifactorial and heterogeneous systemic disease with many underlying pathologic mechanisms having been elucidated; however, the pathomechanism is far from entirely known. This opinion article will demonstrate the potential relevance of the somatosensory Piezo2 microinjury-induced quad-phasic non-contact injury model in psoriasis through a multidisciplinary approach. The primary injury is suggested to be on the Piezo2-containing somatosensory afferent terminals in the Merkel cell−neurite complex, with the concomitant impairment of glutamate vesicular release machinery in Merkel cells. Part of the theory is that the Merkel cell−neurite complex contributes to proprioception; hence, to the stretch of the skin. Piezo2 channelopathy could result in the imbalanced control of Piezo1 on keratinocytes in a clustered manner, leading to dysregulated keratinocyte proliferation and differentiation. Furthermore, the author proposes the role of mtHsp70 leakage from damaged mitochondria through somatosensory terminals in the initiation of autoimmune and autoinflammatory processes in psoriasis. The secondary phase is harsher epidermal tissue damage due to the primary impaired proprioception. The third injury phase refers to re-injury and sensitization with the derailment of healing to a state when part of the wound healing is permanently kept alive due to genetical predisposition and environmental risk factors. Finally, the quadric damage phase is associated with the aging process and associated inflammaging. In summary, this opinion piece postulates that the primary microinjury of our “sixth sense”, or the Piezo2 channelopathy of the somatosensory terminals contributing to proprioception, could be the principal gateway to pathology due to the encroachment of our preprogrammed genetic encoding.

Delayed Onset Muscle Soreness and Critical Neural Microdamage-Derived Neuroinflammation

Piezo2 transmembrane excitatory mechanosensitive ion channels were identified as the principal mechanotransduction channels for proprioception. Recently, it was postulated that Piezo2 channels could be acutely microdamaged on an autologous basis at proprioceptive Type Ia terminals in a cognitive demand-induced acute stress response time window when unaccustomed or strenuous eccentric contractions are executed. One consequence of this proposed transient Piezo2 microinjury could be a VGLUT1/Ia synaptic disconnection on motoneurons, as we can learn from platinum-analogue chemotherapy. A secondary, harsher injury phase with the involvement of polymodal Aδ and nociceptive C-fibers could follow the primary impairment of proprioception of delayed onset muscle soreness. Repetitive reinjury of these channels in the form of repeated bout effects is proposed to be the tertiary injury phase. Notably, the use of proprioception is associated with motor learning and memory. The impairment of the monosynaptic static phase firing sensory encoding of the affected stretch reflex could be the immediate consequence of the proposed Piezo2 microdamage leading to impaired proprioception, exaggerated contractions and reduced range of motion. These transient Piezo2 channelopathies in the primary afferent terminals could constitute the critical gateway to the pathophysiology of delayed onset muscle soreness. Correspondingly, fatiguing eccentric contraction-based pathological hyperexcitation of the Type Ia afferents induces reactive oxygen species production-associated neuroinflammation and neuronal activation in the spinal cord of delayed onset muscle soreness.

Is the Sex Difference a Clue to the Pathomechanism of Dry Eye Disease? Watch out for the NGF-TrkA-Piezo2 Signaling Axis and the Piezo2 Channelopathy

Dry eye disease (DED) is a multifactorial disorder with recognized pathology, but not entirely known pathomechanism. It is suggested to represent a continuum with neuropathic corneal pain with the paradox that DED is a pain-free disease in most cases, although it is regarded as a pain condition. The current paper puts into perspective that one gateway from physiology to pathophysiology could be a Piezo2 channelopathy, opening the pathway to a potentially quad-phasic non-contact injury mechanism on a multifactorial basis and with a heterogeneous clinical picture. The primary non-contact injury phase could be the pain-free microinjury of the Piezo2 ion channel at the corneal somatosensory nerve terminal. The secondary non-contact injury phase involves harsher corneal tissue damage with C-fiber contribution due to the lost or inadequate intimate cross-talk between somatosensory Piezo2 and peripheral Piezo1. The third injury phase of this non-contact injury is the neuronal sensitization process with underlying repeated re-injury of the Piezo2, leading to the proposed chronic channelopathy. Notably, sensitization may evolve in certain cases in the absence of the second injury phase. Finally, the quadric injury phase is the lingering low-grade neuroinflammation associated with aging, called inflammaging. This quadric phase could clinically initiate or augment DED, explaining why increasing age is a risk factor. We highlight the potential role of the NGF-TrkA axis as a signaling mechanism that could further promote the microinjury of the corneal Piezo2 in a stress-derived hyperexcited state. The NGF-TrkA-Piezo2 axis might explain why female sex represents a risk factor for DED.

Membrane Proteins Increase with the Repeated Bout Effect

PURPOSE

The ability of skeletal muscle to adapt to eccentric (ECC) contraction-induced injury is known as the repeated bout effect (RBE). Despite the RBE being a well-established phenomenon observed in skeletal muscle, cellular and molecular events particularly those at the membranes that contribute to the adaptive potential of muscle have yet to be established. Therefore, the purpose of this study was to examine how membrane-associated proteins respond to the RBE.

METHODS

Anterior crural muscles of C57BL/6 female mice (3-5 months) were subjected to repeated bouts of in vivo ECCs, with isometric torque being measured immediately before and after injury. A total of six bouts were completed with 7 d between each bout. Protein content of dystrophin, β-sarcoglycan, and junctophilin were then assessed via immunoblotting in injured and uninjured muscles.

RESULTS

When expressed relative to preinjury isometric torque of bout 1, deficits in postinjury isometric torque during bout 2 (38%) did not differ from bout 1 (36%; P = 0.646) and were attenuated during bouts 3 through 6 (range, 24%-15%; P ≤ 0.014). Contents of dystrophin, β-sarcoglycan, and junctophilin did not change immediately after a single bout of 50 maximal ECCs (P ≥ 0.155); however, as a result of repeated bouts, contents of dystrophin, β-sarcoglycan, and junctophilin all increased compared with muscles that completed one or no bouts of ECC contractions (P ≤ 0.003).

CONCLUSIONS

The RBE represents a physiological measure of skeletal muscle plasticity. Here, we demonstrate that repeated bouts of ECC contractions increase contents of dystrophin, β-sarcoglycan, and junctophilin and attenuate postinjury torque deficits. Given our results, accumulation of membrane-associated proteins likely contributes to strength adaptations observed after repeated bouts of ECC contractions.

Finishing stationary cycling too early after anterior cruciate ligament reconstruction is likely to lead to higher failure

Background

Anterior cruciate ligament injury arises when the knee anterior ligament fibers are stretched, partially torn, or completely torn. Operated patients either end up re-injuring their reconstructed anterior cruciate ligament or majority develop early osteoarthritis regardless of the remarkable improvements of surgical techniques and the widely available rehabilitation best practices. New mechanism theories of non-contact anterior cruciate ligament injury and delayed onset muscle soreness could provide a novel perspective how to respond to this clinical challenge.

Main body

A tri-phasic injury model is proposed for these non-contact injuries. Mechano-energetic microdamage of the proprioceptive sensory nerve terminals is suggested to be the first-phase injury that is followed by a harsher tissue damage in the second phase. The longitudinal dimension is the third phase and that is the equivalent of the repeated bout effect of delayed onset muscle soreness. Current paper puts this longitudinal injury phase into perspective as the phase when the long-term memory consolidation and reconsolidation of this learning related neuronal injury evolves and the phase when the extent of the neuronal regeneration is determined. Reinstating the mitochondrial energy supply and ‘breathing capacity’ of the injured proprioceptive sensory neurons during this period is emphasized, as avoiding fatigue, overuse, overload and re-injury.

Conclusions

Extended use, minimum up to a year or even longer, of a current rehabilitation technique, namely moderate intensity low resistance stationary cycling, is recommended preferably at the end of the day. This exercise therapeutic strategy should be a supplementation to the currently used rehabilitation best practices as a knee anti-aging maintenance effort.

Increasing the resting time between drop jumps lessens delayed-onset muscle soreness and limits the extent of prolonged low-frequency force depression in human knee extensor muscles

PURPOSE

Unaccustomed eccentric contractions generally result in a long-lasting contractile impairment, referred to as prolonged low-frequency force depression (PLFFD), and delayed-onset muscle soreness (DOMS). We here used repeated drop jumps (DJs) as an eccentric contraction model and studied the effects of increasing the time between DJs from 20 s to 5 min. We hypothesized that both PLFFD and DOMS would be less marked at the longer DJ interval due to the longer time to restore structural elements between DJs.

METHODS

Young men (n = 12) randomly performed 50 DJs with either 20-s (DJ-20 s) or 5-min (DJ-5 min) rest between DJs. Voluntary, 20 Hz and 100 Hz electrically stimulated isometric knee extension torques and muscle soreness were monitored before and for 7 days after DJs; serum CK activity was measured to assess muscle fibre protein leakage. In additional experiments, changes in mRNA levels were assessed in muscle biopsies collected before and 1 h after exercise.

RESULTS

A marked PLFFD was observed with both protocols and the extent of 20 Hz torque depression was smaller immediately and 1 day after DJ-5 min than after DJ-20 s (p < 0.05), whereas the MVC and 100 Hz torques were similarly decreased with the two protocols. Markedly larger differences between the two protocols were observed for the muscle soreness score, which 1-4 days after exercise was about two times larger with DJ-20 s than with DJ-5 min (p < 0.01).

CONCLUSIONS

The larger protective effect of the longer DJ interval against DOMS than against PLFFD indicates that their underlying mechanisms involve different structural elements.

Effect of Leg Eccentric Exercise on Muscle Damage of the Elbow Flexors after Maximal Eccentric Exercise

PURPOSE

The magnitude of muscle damage induced by maximal eccentric exercise is attenuated when the same exercise is repeated by homologous muscle of the ipsilateral or contralateral limb. It is not known if the muscle damage-protective effect is also transferred to nonhomologous muscles. The present study investigated the effects of unilateral knee extensor (KE) or flexor (KF) eccentric exercise on muscle damage induced by elbow flexor (EF) eccentric exercise of the ipsilateral or contralateral side.

METHODS

Young healthy sedentary men were assigned to four experimental groups (n = 13 per group) that performed five sets of six maximal eccentric contractions (MaxEC) of the KE or KF of the same or opposite side of the arm that performed MaxEC of the EF 1 wk later, and a control group that performed two bouts of MaxEC of the EF using a different arm for each bout separated by 1 wk. Changes in several indirect muscle damage markers were compared among the groups by mixed-design, two-way ANOVA.

RESULTS

Changes in maximal voluntary concentric contraction torque, range of motion, muscle soreness, and plasma creatine kinase activity after KE or KF MaxEC were not different (P > 0.05) between legs, but greater (P < 0.05) after KF than KE MaxEC. The changes in the variables after EF MaxEC in the experimental groups were not different (P > 0.05) from the first bout of the control group but larger (P < 0.05) than the second bout of the control group, and no differences between the ipsilateral and contralateral sides were evident.

CONCLUSIONS

These results showed that no protective effect on EF MaxEC was conferred by the leg exercises, suggesting that muscle damage protection was not transferred from KE or KF to EF.

No Effect of Acute Eccentric Resistance Exercise on Immune Responses to Influenza Vaccination in Older Adults: A Randomized Control Trial

INTRODUCTION

Older adults are at elevated risk for morbidity and mortality caused by influenza. Vaccination is the primary means of prophylaxis, but protection is often compromised in older adults. As resistance exercise mobilizes immune cells into muscle, it may enhance vaccination response.

PURPOSE

Compare antibody and cell mediated immune responses to influenza vaccination in older adults who performed eccentric resistance exercise immediately prior to vaccination to those who did not exercise.

METHODS

Twenty nine resistance training-naive older adults (20 women, 73.9 ± 5.3 years) were randomized to 1 of 3 groups: vaccination in the same arm that exercised (Ex-S), vaccination in the opposite arm that exercised (Ex-Op), and seated rest (No-Ex). Exercise consisted of 10 sets of 5 eccentric unilateral repetitions at 80% of the pre-determined concentric one repetition maximum. Lateral raises were alternated with bicep curls. No-Ex sat quietly for 25 min. Following exercise or rest, all received the 2018 quadrivalent influenza vaccine (Seqirus Afluria) in the non-dominant deltoid. Antibody titers against each influenza vaccine strain were determined by hemagglutinin inhibition assays at baseline, 6-, and 24-weeks post-vaccination. Influenza-specific T cells were quantified after stimulation with the vaccine by intracellular cytokine staining.

RESULTS

No significant group x time effects were found in antibody responses to any strain (interaction for A/H1N1: p = 0.682; A/H3N2: p = 0.644; B/Colorado/06/2017: p = 0.262; B/Phuket/3073/2013: p = 0.851). Groups did not differ in fold-increase of antibody titers 6- and 24-weeks post-vaccination. Influenza-specific T-cells did not differ between groups at any time (comparison at baseline: p = 0.985; 6-weeks: p = 0.889; 24 weeks: p = 0.857). One subject (Ex-S) reported flu-like symptoms 18 weeks post-vaccination.

CONCLUSION

Acute arm eccentric exercise did not influence antibody titers or cell mediated immune responses to the influenza vaccine delivered post-exercise in older adults. More strenuous exercise may be required for exercise to act as an adjuvant. ClinicalTrials.gov Identifier: NCT03736759.

Eccentric exercise causes delayed sensory nerve conduction velocity but no repeated bout effect in the flexor pollicis brevis muscles

PURPOSE

This study was aimed at investigating the effect of eccentric contractions (ECCs) of flexor pollicis brevis muscles (FPBMs) on motor and sensory nerve functions as well as the ipsilateral repeated bout effect (IL-RBE) and contralateral (CL)-RBE of motor and sensory nerve conduction velocities following ECCs.

METHODS

Thirty-two young healthy men (age: 19.6 ± 0.2 years, height: 173.2 ± 1.2 cm, body mass: 69.7 ± 1.9 kg) performed two bouts of ECCs. During the first ECCs bout (ECCs-1), all participants performed 100 ECCs with 1 hand; for the second bout, 3 groups (2 weeks [W]: n = 11, 4W: n = 10, 8W: n = 11) performed ECCs with both hands 2, 4, or 8 weeks after ECCs-1. The maximal voluntary isometric contraction (MVC), range of motion (ROM), visual analog scale for pain (VAS), motor and sensory nerve conduction velocities were measured before, immediately after, and 1, 2, 3, and 5 days after ECCs.

RESULTS

ECCs-1 decreased the MVC, limited the ROM, developed VAS, and decreased the motor and sensory nerve conduction velocities compared to non-exercise hand (p < 0.05). The repeated bout effect was observed in the ROM for IL-RBE in 2W and 4W, VAS for IL-RBE in 2 W, and ROM and VAS for CL-RBE in 2W (p < 0.05). However, RBEs of MVC and motor and sensory nerve conduction velocities were not observed, and no differences were confirmed depending on the interval.

CONCLUSION

In the present study, ECCs of the FPBM caused a sensory nerve dysfunction, while IL- or CL-RBE was not observed.

Post Orgasmic Illness Syndrome (POIS) and Delayed Onset Muscle Soreness (DOMS): Do They Have Anything in Common?

Post orgasmic illness syndrome is a rare, mysterious condition with an unknown pathomechanism and uncertain treatment. The symptoms of post orgasmic illness syndrome last about 2–7 days after an ejaculation. The current hypothesis proposes that the primary injury in post orgasmic illness syndrome is an acute compression proprioceptive axonopathy in the muscle spindle, as is suspected in delayed onset muscle soreness. The terminal arbor degeneration-like lesion of delayed onset muscle soreness is theorized to be an acute stress response energy-depleted dysfunctional mitochondria-induced impairment of Piezo2 channels and glutamate vesicular release. The recurring symptoms of post orgasmic illness syndrome after each ejaculation are suggested to be analogous to the repeated bout effect of delayed onset muscle soreness. However, there are differences in the pathomechanism, mostly attributed to the extent of secondary tissue damage and to the extent of spermidine depletion. The spermidine depletion-induced differences are as follows: modulation of the acute stress response, flu-like symptoms, opioid-like withdrawal and enhanced deregulation of the autonomic nervous system. The longitudinal dimension of delayed onset muscle soreness, in the form of post orgasmic illness syndrome and the repeated bout effect, have cognitive and memory consequences, since the primary injury is learning and memory-related.

Moderate intensity cycling is better than running on recovery of eccentric exercise-induced muscle damage

OBJECTIVE

To compare the effects of moderate intensity running and cycling on markers of exercise-induced muscle damage in men.

STUDY DESIGN

Randomized controlled trial.

SETTING

Laboratory.

PARTICIPANTS

Thirty volunteers were randomized in three groups [running (RG; n = 10), cycling (CG; n = 10) and control (CON; n = 10)] and were evaluated at baseline, post 24, 48 and 72 h of knee extensors' muscle damage protocol. CON performed passive recovery, while RG and CG performed active recovery immediately after the protocol, as well as 24 h and 48 h afterwards.

MAIN OUTCOMES

(i) maximal voluntary isometric contraction (MVIC); (ii) delayed-onset muscle soreness (DOMS); (iii) plasma creatine kinase (CK) and lactate dehydrogenase (LDH) levels.

RESULTS

No group-by-time interaction was found in any outcome evaluated (p > 0.05). All groups presented decreases in MVIC and increases in DOMS (p < 0.001), without differences in CK and LDH. Compared with CON, exercise groups presented likely beneficial effects for LDH, while only CG had a likely beneficial effect for DOMS. Lastly, CG presented likely/very likely beneficial effects for MVIC and DOMS compared to RG.

CONCLUSION

Although the null hypothesis analysis did not find differences, the magnitude-based inference analysis suggested that moderate intensity cycling have likely beneficial effects on knee extensor muscle recovery after eccentric exercise protocol.

Effect of Arm Eccentric Exercise on Muscle Damage of the Knee Flexors After High-Intensity Eccentric Exercise

Repeated bout effect (RBE) describes a phenomenon that an initial unaccustomed eccentric exercise (ECC) bout can confer a protective effect against muscle damage from the subsequent same exercise. This protection has been observed in the same muscle, as well as the contralateral homologous (CL-RBE) muscle. But it is unknown whether the RBE is evident for non-local unrelated heterogonous muscles. The purpose of this study was to examine whether an initial elbow flexion (EF) muscle-damaging ECC could confer RBE against muscle damage from the subsequent ECC performed in the remote lower limb knee flexor (KF) muscle group. Twenty-seven young individuals were randomly assigned into the experimental (EXP: n = 15) and the control (CON: n = 12) groups. All participants performed a baseline unilateral KF ECC (six sets of 10 repetitions) on a randomly chosen leg. After a washout period (4 weeks), the EXP group performed 60 high-intensity unilateral EF ECC on a randomly chosen arm, followed by the same intensity exercise using the contralateral KF muscle group 2 weeks later. The CON group performed the same contralateral KF ECC, but with no prior EF ECC bout. Changes in the KF muscle damage indirect markers (muscle soreness, range of motion, and maximal isometric strength) after the ECC were compared between the baseline and second bouts for both groups with mixed factorial three-way (group × bout × time) ANOVA. Additionally, index of protection for each damage marker was calculated at 1 and 2 days after the ECC and compared between groups with independent t-tests. For both groups, the magnitude of the changes in the damage markers between the baseline and the second ECC bouts were not significantly different (all values of p > 0.05). As for the index of protection, relative to the CON, the EXP showed an exacerbating damaging effect on the KF isometric strength following the second ECC bout, particularly at the 1-day post-exercise time point (index of protection: EXP vs. CON mean ± SD = -29.36 ± 29.21 vs. 55.28 ± 23.83%, p = 0.040). Therefore, our results do not support the existence of non-local RBE.

Muscle Damage and Overreaching During Wildland Firefighter Critical Training

OBJECTIVE

To document the effects of wildland firefighter (WLFF) critical training (CT) on physiologic markers of muscle damage and acute overreaching.

METHODS

Eighteen male and three female WLFFs were studied during an 11-day CT. Upper-body (US), lower-body (LS) muscle soreness and body weight (BW) were collected daily. Blood was collected on days 1, 4, 8, and 11 to measure creatine kinase (CK), lactate dehydrogenase (LDH), cortisol, and testosterone. Skinfolds were taken on days 1 and 11 to estimate body fat (BF) and lean body weight (LBW).

RESULTS

CT resulted in a significant depression in BF and elevation in LBW, while main effects of time were seen in US, LS, CK, LDH, cortisol, and testosterone/cortisol ratio (P < 0.05).

CONCLUSION

These data suggest WLFFs undergo significant physiological stressors resulting in muscle soreness, damage, and possible overreaching during CT.

Urinary N-terminal fragment of titin: A surrogate marker of serum creatine kinase activity after exercise-induced severe muscle damage

We aimed to evaluate whether changes in the noninvasively assessed urinary N-terminal fragment of titin (U-titin) concentration may be associated with those of serum creatine kinase (CK) activity, transverse relaxation time (T₂), maximal voluntary contraction (MVC) torque, range of motion (ROM), and muscle soreness, following high-intensity eccentric exercise. Twenty-eight healthy young men performed 30 maximal isokinetic (120°/s) eccentric elbow flexor contractions using an isokinetic dynamometer. U-titin concentration, serum CK activity, T₂, MVC torque, ROM, and muscle soreness were measured before and after a maximum of 4 days. Both U-titin concentration and serum CK activity increased post-exercise in a similar manner, though the former elevated slightly earlier (p < 0.05). The peak values of log U-titin concentration following eccentric exercise were strongly correlated with those of log serum CK activity (r = 0.90, p < 0.05) and T₂ (r = 0.84, p < 0.05). There were moderate correlations between peak values of U-titin concentration and those of MVC torque (r = 0.69, p < 0.05) and ROM decline rate (r = 0.45, p < 0.05). These results suggest that in healthy young men, the non-invasive marker, U-titin, may be used as a serum CK surrogate following exercise-induced severe muscle damage.

Application of traditional Chinese therapy in sports medicine

Chinese herbs have been used as dietary supplements to improve exercise performance. However, evidence-based studies for the use of Chinese herbs in sports remain scarce. Traditional Chinese therapy (TCT), a form of traditional Chinese non-pharmacological intervention, has remained in use for thousands of years in sports medicine. TCT is beneficial for sports injuries and in enhancing skill development, and is becoming increasingly popular among athletes, fitness enthusiasts, and individuals who regularly exercise. The therapeutic effects of TCT have been demonstrated by clinical and experimental studies, but using these modalities still is associate with potentially adverse effects. Further well-designed studies are necessary to confirm the efficacy of TCT in sports medicine. This review aims to summarize the application of TCT, discuss the issues surrounding TCT clinical research, and provide suggestions for applying traditional Chinese methods in the field of sports medicine.

Muscle Strength Does Not Adapt From a Second to Third Bout of Eccentric Contractions: A Systematic Review and Meta-Analysis of the Repeated Bout Effect

ABSTRACT

Lindsay, A, Abbott, G, Ingalls, CP, and Baumann, CW. Muscle strength does not adapt from a second to third bout of eccentric contractions: A systematic review and meta-analysis of the repeated bout effect. J Strength Cond Res 35(2): 576-584, 2021-The greatest muscle strength adaptations to repeated bouts of eccentric contractions (ECC) occur after the initial injury, with little to no change in subsequent bouts. However, because of the disparity in injury models, it is unknown whether three or more bouts provide further adaptation. Therefore, we performed a systematic review of the literature to evaluate whether a third bout of skeletal muscle ECC impacts immediate strength loss and rate of strength recovery compared with a second bout. A search of the literature in Web of Science, SCOPUS, Medline, and the American College of Sports Medicine database was conducted between May and September 2019 using the keywords eccentric contraction or lengthening contraction and muscle and repeated or multiple, and bout. Eleven studies with 12 experimental groups, using 72 human subjects, 48 mice, and 11 rabbits, met the inclusion criteria. A meta-analysis using a random effects model and effect sizes (ESs; Hedges' g) calculated from the standardized mean differences was completed. Calculated ESs for immediate strength loss provided no evidence that a third bout of ECC results in greater loss of strength compared with a second bout (ES = -0.12, 95% confidence interval [CI] = -0.41 to 0.17). Furthermore, the rate of strength recovery was not different between a second and third bout (ES = -0.15, 95% CI = -1.01 to 0.70). These results indicate a third bout of skeletal muscle ECC does not improve indices of strength loss or rate of strength recovery compared with a second bout. Therefore, coaches and athletes should expect some level of persistent weakness after each of their initial training sessions involving ECC, and the faster recovery of strength deficits in the second bout documented by previous research is not different from a third bout.

Delayed Onset Muscle Soreness (DOMS): The Repeated Bout Effect and Chemotherapy-Induced Axonopathy May Help Explain the Dying-Back Mechanism in Amyotrophic Lateral Sclerosis and Other Neurodegenerative Diseases

Delayed onset muscle soreness (DOMS) is hypothesized to be caused by glutamate excitotoxicity-induced acute compression axonopathy of the sensory afferents in the muscle spindle. Degeneration of the same sensory afferents is implicated in the disease onset and progression of amyotrophic lateral sclerosis (ALS). A series of “silent” acute compression proprioceptive axonopathies with underlying genetic/environmental factors, damaging eccentric contractions and the non-resolving neuroinflammatory process of aging could lead to ALS disease progression. Since the sensory terminals in the muscle spindle could not regenerate from the micro-damage in ALS, unlike in DOMS, the induced protective microcircuits and their long-term functional plasticity (the equivalent of the repeated bout effect in DOMS) will be dysfunctional. The acute stress invoking osteocalcin, bradykinin, COX1, COX2, GDNF, PGE2, NGF, glutamate and N-methyl-D-aspartate (NMDA) receptors are suggested to be the critical signalers of this theory. The repeated bout effect of DOMS and the dysfunctional microcircuits in ALS are suggested to involve several dimensions of memory and learning, like pain memory, inflammation, working and episodic memory. The spatial encoding of these memory dimensions is compromised in ALS due to blunt position sense from the degenerating proprioceptive axon terminals of the affected muscle spindles. Dysfunctional microcircuits progressively and irreversibly interfere with postural control, with motor command and locomotor circuits, deplete the neuroenergetic system, and ultimately interfere with life-sustaining central pattern generators in ALS. The activated NMDA receptor is suggested to serve the “gate control” function in DOMS and ALS in line with the gate control theory of pain. Circumvention of muscle spindle-loading could be a choice of exercise therapy in muscle spindle-affected neurodegenerative diseases.

Exercise-induced muscle damage: mechanism, assessment and nutritional factors to accelerate recovery

There have been a multitude of reviews written on exercise-induced muscle damage (EIMD) and recovery. EIMD is a complex area of study as there are a host of factors such as sex, age, nutrition, fitness level, genetics and familiarity with exercise task, which influence the magnitude of performance decrement and the time course of recovery following EIMD. In addition, many reviews on recovery from exercise have ranged from the impact of nutritional strategies and recovery modalities, to complex mechanistic examination of various immune and endocrine signaling molecules. No one review can adequately address this broad array of study. Thus, in this present review, we aim to examine EIMD emanating from both endurance exercise and resistance exercise training in recreational and competitive athletes and shed light on nutritional strategies that can enhance and accelerate recovery following EIMD. In addition, the evaluation of EIMD and recovery from exercise is often complicated and conclusions often depend of the specific mode of assessment. As such, the focus of this review is also directed at the available techniques used to assess EIMD.

Effectiveness of a combined New Zealand green-lipped mussel and Antarctic krill oil supplement on markers of exercise-induced muscle damage and inflammation in untrained men

Green-lipped mussel oil (PCSO-524^®) has been shown to attenuate signs and symptoms of exercise-induced muscle damage (EIMD), and krill oil has been shown to have a protective effect against cytokine-induced tissue degradation. The purpose of this study was to compare the effects of PCSO-524^® and ESPO-572^® (75% PCSO-524^® and 25% krill oil) on signs and symptoms of EIMD. Fifty-one untrained men consumed 600 mg/d of PCSO-524^® (n = 24) or ESPO-572^® (n = 27) for 26 d prior to and 72 h following a downhill running bout. Delayed onset muscle soreness (DOMS), pressure pain threshold, limb swelling, range of motion (ROM), isometric torque, and blood markers of inflammation and muscle damage were assessed at baseline, 24, 48 and 72 h post-eccentric exercise. ESPO-572^® was 'at least as good as' PCSO-524^® and both blends were superior (p < 0.05) to placebo in lessening the increase in DOMS at 24, 48, 72 h. ESPO-572^® and PCSO-524^® were protective against joint ROM loss compared to placebo (p < 0.05) at 48 and 72 h. Notably, at 24 and 48 h, joint ROM was higher in the ESPO-572^® compared to the PCSO-524^® group (p < 0.05). No differences between the two blends for the other markers were found. ESPO-572^® is 'at least as good' as PCSO-524^® in reducing markers of muscle damage and soreness following eccentric exercise and was superior to PCSO-524^® in protecting against the loss in joint ROM during recovery. Our data support the use of ESPO-572^®, a combination of green-lipped mussel and krill oil, in mitigating the deleterious effects of EIMD.

Low Body Fat Does Not Influence Recovery after Muscle-Damaging Lower-Limb Plyometrics in Young Male Team Sport Athletes

AIM

This study assessed the influence of fat mass to fat-free mass ratio (FM:FFM) on recovery from plyometric exercise.

METHOD

After assessment of body composition, 20 male team sport players (age 20.7 ± 1.1 years; body mass 77.1 ± 11.5 kg) were divided into low- (n = 10; 0.11 ± 0.03) and normal- (n = 10; 0.27 ± 0.09) fat groups based on FM:FFM ratio. Thereafter, participants completed measurements of knee extensor torque at 60 and 240°∙s-1, countermovement jump flight time, plasma creatine kinase (CK) activity and perceived muscle soreness (VAS) before and at 0, 24 and 48 h after 10 × 10 maximal plyometric vertical jumps.

RESULTS

Evidence of muscle damage was confirmed by alterations in VAS, peak torque at 60 and 240°∙s-1 and flight time at 0, 24 and 48 h after plyometric exercise (P < 0.05). CK was increased at 0 and 24 h (P < 0.05) but returned to baseline values by 48 h. No time by group effects were observed for any of the dependent variables (P > 0.05).

CONCLUSION

The current findings indicate that while muscle damage was present after plyometric exercise, the magnitude was similar across the two body composition groups. Applied practitioners can allow for a similar recovery time after plyometric exercise in those with low and normal body fat.

Resistance Training Acutely Impairs Agility and Spike-Specific Performance Measures in Collegiate Female Volleyball Players Returning from the Off-Season

This study examined the acute effects of resistance training (RT) on volleyball-specific performance. Sixteen female volleyball players undertook their initial, pre-season RT bout. Countermovement jump (CMJ), delayed onset of muscle soreness (DOMS), and sport-specific performances (i.e., run-up jump, agility, and spiking speed and accuracy) were measured before, 24 (T24), and 48 (T48) hours after RT. A significant increase in DOMS was observed at T24 and T48 (~207.6% ± 119.3%; p < 0.05; ES = 1.8 (95% CI: 0.94–2.57)), whilst agility was significantly impaired at T48 (1.7% ± 2.5%; p < 0.05; ES = 0.30 (95% CI: −0.99–0.40)). However, there were no differences in CMJ (~−2.21% ± 7.6%; p > 0.05; ES = −0.11 (95% CI: −0.80–0.58)) and run-up jump (~−1.4% ± 4.7%; p > 0.05; ES = −0.07 (95% CI: −0.76–0.63)). Spiking speed was significantly reduced (−3.5% ± 4.4%; p < 0.05; ES = −0.28 (95% CI: −0.43–0.97)), although accuracy was improved (38.3% ± 81.4%: p < 0.05) at T48. Thus, the initial, preseason RT bout compromised agility and spiking speed for several days post-exercise. Conversely, spiking accuracy improved, suggesting a speed–accuracy trade-off. Nonetheless, at least a 48-h recovery may be necessary after the initial RT bout for athletes returning from the off-season or injury.

Influence of curcumin on performance and post-exercise recovery

Intense exercise, especially involving eccentric contractions, causes muscle damage concomitant with increased reactive oxygen species (ROS), which can lead to increased fatigue and decrements in physical performance. Additionally, inflammatory cytokines and advanced glycation end-products (AGEs) are produced as a result of eccentric exercise and may further lead to decreased exercise performance. Nutritional interventions may provide an avenue to respond to and reduce the symptoms associated with muscle damage. Of recent interest, curcumin, the main constituent in the spice turmeric, has been the focus of various studies considering post-exercise recovery. Curcumin has potent anti-oxidant and anti-inflammatory properties and can reduce the accumulation of AGEs. This review considers the current evidence for curcumin to impact muscle recovery following exercise to improve performance and the potential mechanisms of action. To date, clinical studies have considered the potential role of curcumin to reduce muscular damage following treadmill running (downhill and flat), conventional walking/running, cycling (acute and chronic), single-leg jumping (downhill), and eccentric muscular fitness exercises of the upper and lower body (single- and double-leg). Studies have been conducted in sedentary to highly active men and women, both young and old, with supplementation duration lasting from a single, acute dose to daily dosages for three months. Various curcumin-based interventions have improved self-perceived measures of pain and tenderness, reduced evidence of muscle damage, ameliorated inflammatory markers, increased markers of antioxidant capacity, diminished markers of oxidative stress, reduced markers of AGEs, and attenuated loss in mean power of single-leg sprints. However, these findings have not been consistently reported.

The effect of essential oil of rosemary on eccentric exercise-induced delayed-onset muscle soreness in non-active women

Muscle soreness is a problem associated with physical activities. Recently, the medicinal herbs are strategies to prevent muscle soreness. The present study aims were to determine the effect of rosemary essential oil on the responses of lactate dehydrogenase, creatine kinase (CK), lymphocytes, neutrophils, muscle swelling (MS) and muscle pain (MP) following eccentric leg curl exercise in non-active women. 24 non-active females voluntarily participated in this study and were randomly assigned into three groups: rosemary dose 1 (RD1) (n=8; 0.25 ml), rosemary dose 2 (RD2) (n=8; 0.5 ml) and placebo (n=8; 0.5 ml olive oil). Participants in supplement groups consumed the desire amounts of rosemary essential oil every 8 h per day for 14 days. Then, the eccentric leg curl exercise was performed. The supplementation continued until 72 h after exercise. The serum variables, as well as, MS and MP were measured before, 24, 48 and 72 h after exercise. Data were analysed using repeated measure analysis of variance and P≤0.05 considered as significant. The results showed that rosemary significantly decreases CK in RD2 compared with placebo and RD1 48 h after exercise. There was no other significant difference in other serum variables. In conclusion, the present study showed a beneficial effect of rosemary on 48-h post-exercise serum CK concentration (a muscle damage indicator).

Transcriptional memory in skeletal muscle. Don't forget (to) exercise

Transcriptional memory describes an ancient and highly conserved form of cellular learning that enables cells to benefit from recent experience by retaining a mitotically inheritable but reversible memory of the initial transcriptional response when encountering an environmental or physiological stimulus. Herein, we will review recent progress made in the understanding of how cells can make use of diverse constituents of the epigenetic toolbox to retain a transcriptional memory of past states and perturbations. Specifically, we will outline how these mechanisms will help to improve our understanding of skeletal muscle plasticity in health and disease. We describe the epigenetic road map that allows skeletal muscle fibers to navigate through training-induced adaptation processes, and how epigenetic memory marks can preserve an autobiographical history of lifestyle behavior changes, pathological challenges, and aging. We will further consider some key findings in the field of exercise epigenomics to emphasize major challenges when interpreting dynamic changes in the chromatin landscape in response to acute exercise and training.

Effect of eccentric overload through isoinertial technology in basketball players

Abstract The present study investigated the effect of eccentric overload on professional basketball players. Participants were 8 players aged 18-25 years who play in a Leb Oro League team. There was an 8 week training cycle with 1 weekly session of half squats. The control group performed training following a traditional methodology –using free weights– whereas the experimental group used inertial technology, that is, the ProSquat machine from Proinertial®. Both vertical jump and 30-meter sprint were assessed before and after intervention. The following conclusions were reached: a) strength training with vertical vector improves the 30-meter sprint test and also the vertical jump; b) training program that affects the eccentric overload of the movement results in more improvements than traditional training with the same duration; c) training in the vertical vector also has an impact on the way force is manifested in the horizontal vector, showing improvements in the 30-meter sprint.

Changes in urinary titin N-terminal fragments as a biomarker of exercise-induced muscle damage in the repeated bout effect

OBJECTIVES

Muscle damage symptoms induced by unaccustomed eccentric contraction exercise can be reduced by repeating the experience several times. This phenomenon is termed the repeated bout effect. Although traditional biochemical markers require invasive blood sampling, biochemical measurements have recently been developed that can be non-invasively performed using urinary titin N-terminal fragment (UTF). However, it is unclear whether UTF can reflect the repeated bout effect. Therefore, the aim of the present study was to clarify whether UTF decreased with the repeated bout effect.

DESIGN

This study compared changes in muscle damage markers between bouts of exercise performed for the first and second time.

METHODS

Eight young men performed 30 eccentric exercises of the elbow flexor on the first day of the first week (Bout 1). A second bout of eccentric exercises, same as the first, was performed 2 weeks later, (Bout 2). The dependent variables were muscle soreness (SOR), maximal voluntary isometric contraction (MVIC), range of motion (ROM), creatine kinase (CK), and UTF. All dependent variables were analyzed using two-way analysis of variance.

RESULTS

No significant difference was observed in workload or peak torque between the first and second exercise bouts. SOR as well as CK and UTF were significantly lower and ROM and MVIC were significantly higher in Bout 2 in comparison to Bout 1.

CONCLUSIONS

These results suggest that UTF sensitively reflects the repeated bout effect and exercise-induced muscle damage can be non-invasively measured.

Monitoring exercise-induced muscle damage indicators and myoelectric activity during two weeks of knee extensor exercise training in young and old men

This study considered the effects of repeated bouts of short-term resistive exercise in old (age: 64.5±5.5 years; n = 10) and young men (age: 25.1±4.9 years; n = 10) who performed six knee extension exercise bouts over two weeks using various markers of exercise-induced muscle damage and electromyographic activity. We found that time-course changes in quadriceps isometric torque, creatine kinase activity, and muscle soreness in the two groups were similar. However, recovery in the acute torque deficit was mediated by more favourable electromyographic activity changes in the young group than in the older adults group. Muscle elastic energy storage and re-use assessed with dynamometry was selectively improved in the young group by the end of the protocol. Serum myoglobin concentration increased selectively in old group, and remained elevated with further bouts, suggesting higher sarcolemma vulnerability and less effective metabolic adaptation in the older adults, which, however, did not affect muscle contractility.

The contribution of low-frequency fatigue to the loss of quadriceps contractile function following repeated drop jumps

NEW FINDINGS

What is the central question of this study? Why do some subjects recover slowly following a bout of eccentric exercise and why is recovery faster following a repeated bout? What is the main finding and its importance? The results are consistent with two major causes of the reduction of quadriceps torque, the onset of low-frequency fatigue which recovered relatively fast and a second, delayed form of damage. Differences in the delayed damage process largely accounted for the differences in the rate of torque recovery between subjects after a first bout and it was suppression of the delayed damage which accounted for the faster recovery following a repeated bout of eccentric exercise.

ABSTRACT

The purpose of this study was to determine the extent to which low-frequency fatigue (LFF) accounts for the loss of quadriceps strength and time course of recovery following a series of drop jumps (DJs). Seventeen female subjects (20.8 ± 1.4 years) undertook 100 DJs, which were repeated 4 weeks later. Maximum isometric torque (MIT) and the ratio of torque generated by 20 and 100 Hz electrical stimulation (20/100), as a measure of LFF, were measured over 7 days following each series of DJs. After the first series the 20/100 ratio fell to a greater extent than MIT (to 35 ± 8.7% and 69 ± 11%, respectively) but recovered over 2-3 days, while MIT showed little recovery over this time. Changes of the 20/100 ratio were similar between subjects with fast or slow MIT recovery. Following the second series of DJs, changes in the 20/100 ratio were similar to those of the first bout and there were no differences between fast and slow recovering subjects. MIT, however, recovered more rapidly than after the first bout; the faster recovery was confined to the subjects who recovered slowly following the first bout. The results are consistent with two major causes of the reduction of quadriceps torque, the onset of low-frequency fatigue which recovered relatively fast and a second, delayed, form of damage. The latter largely accounted for the differences in MIT recovery between subjects after the first bout, while suppression of the delayed damage accounted for the faster recovery following the repeated bout.

Exercise-Induced Muscle Damage and Recovery in Young and Middle-Aged Males with Different Resistance Training Experience

This study compared the time course of recovery after a squatting exercise in trained young (YG; n = 9; age 22.3 ± 1.7 years) and trained (MT; n = 9; 39.9 ± 6.2 years) and untrained (MU; n = 9; age 44.4 ± 6.3 years) middle-aged males. Before and at 24 and 72 h after 10 × 10 squats at 60% one-repetition maximum (1RM), participants provided measurements of perceived muscle soreness (VAS), creatine kinase (CK), maximal voluntary contraction (MVC), voluntary activation (VA), and resting doublet force of the knee extensors and squatting peak power at 20% and 80% 1RM. When compared to the YG males, the MT experienced likely and very likely moderate decrements in MVC, resting doublet force, and peak power at 20% and 80% 1RM accompanied by unclear differences in VAS, CK, and VA after the squatting exercise. MU males, compared to MT, experienced greater alterations in peak power at 20% and 80% 1RM and VAS. Alterations in CK, MVC, VA, and resting doublet force were unclear at all time-points between the middle-aged groups. Middle-aged males experienced greater symptoms of muscle damage and an impaired recovery profile than young resistance trained males. Moreover, regardless of resistance training experience, middle-aged males are subject to similar symptoms after muscle-damaging lower-body exercise.

Eccentric Muscle Contractions: Risks and Benefits

Eccentric contractions, characterized by the lengthening of the muscle-tendon complex, present several unique features compared with other types of contractions, which may lead to unique adaptations. Due to its specific physiological and mechanical properties, there is an increasing interest in employing eccentric muscle work for rehabilitation and clinical purposes. However, unaccustomed eccentric exercise is known to cause muscle damage and delayed pain, commonly defined as “Delayed-Onset Muscular Soreness” (DOMS). To date, the most useful preventive strategy to avoid these adverse effects consists of repeating sessions involving submaximal eccentric contractions whose intensity is progressively increased over the training. Despite an increased number of investigations focusing on the eccentric contraction, a significant gap still remains in our understanding of the cellular and molecular mechanisms underlying the initial damage response and subsequent adaptations to eccentric exercise. Yet, unraveling the molecular basis of exercise-related muscle damage and soreness might help uncover the mechanistic basis of pathological conditions as myalgia or neuromuscular diseases. In addition, a better insight into the mechanisms governing eccentric training adaptations should provide invaluable information for designing therapeutic interventions and identifying potential therapeutic targets.

C-Reactive Protein Is Elevated Only in High Creatine Kinase Responders to Muscle Damaging Exercise

The purpose of this study was to investigate if exertional rhabdomyolysis induced by an acute bout of plyometric exercise in untrained individuals was associated with histological characteristics of skeletal muscle, creatine kinase (CK) polymorphism or secondary damage. Twenty-six healthy male untrained individuals completed a bout of plyometric exercise (10 sets of 10 maximal squat jumps, with each standardized to achieve at least 95% of individual maximal jump height). Blood samples were taken, and perceived pain was scored immediately before the exercise intervention and 6 h, 1, 2, and 3 days post-intervention. Muscle biopsies were collected 9 or 4 days before (baseline) and 3 days after plyometric jumps. Subjects were divided into two groups, high (n = 10) and low responders (n = 16), based on a cut-off limit for exertional rhabdomyolysis of peak CK activity ≥ 1000 U/L in any post-exercise blood sample. Perceived pain was more severe assessed in squat than standing position. Low responders perceived more pain at 6 h and 1 day, while high responders perceived more pain than low responders on days three and four after exercise; structural (dystrophin staining) and ultra-structural (transmission electron microscopy) analysis of muscle fibers revealed no baseline pathology; damage was evident in all individuals in both groups, with no difference between high and low responders in either damage or fiber type proportion. High responders had significantly higher total white blood cell and neutrophil counts 6 h and significantly higher C-reactive protein (CRP) 6 h and days one and two after exercise compared to low responders. High responders had significantly greater muscle myeloperoxidase (MPO) levels in baseline and 3 day post-exercise biopsies compared to baseline of low responders. MLCK C49T single polymorphism was present in 26% of volunteers, whose CK responses were not higher than those with MLCK CC or CT genotype. In conclusion, perceived pain is more effectively assessed with potentially affected muscle under eccentric strain, even if static. High CK responders also have pronounced CRP responses to unaccustomed plyometric exercise intervention. Exertional rhabdomyolysis after unaccustomed eccentric exercise may be related to underlying inability to resolve intramuscular MPO.

Damage and the repeated bout effect of arm, leg, and trunk muscles induced by eccentric resistance exercises

This study compared nine resistance eccentric exercises targeting arm, leg, and trunk muscles in one session for changes in maximal voluntary isometric contraction strength (MVC), delayed onset muscle soreness (DOMS), plasma creatine kinase (CK) activity, and myoglobin (Mb) concentration after the first and second bouts. Fifteen sedentary men (20-25 years) performed 5 sets of 10 eccentric contractions with 80% of MVC load for the elbow flexors (EF), elbow extensors (EE), pectoralis, knee extensors (KE), knee flexors (KF), plantar flexors (PF), latissimus, abdominis, and erector spinae (ES) in a randomized order and repeated the same exercises 2 weeks later. MVC decreased at 1 (16%-57%) to 4 (13%-49%) days, DOMS developed (peak: 43-70 mm), and CK activity (peak: 23 238-207 304 IU/L) and Mb concentration showed large increases after the first bout. The magnitude of decrease in MVC was greater (P < 0.05) for EF, EE, and PEC than others and for KF than KE, PF, and ES. DOMS was greater (P < 0.05) for EF, EE, and ES than others. Changes in all measures were smaller (P < 0.05) after the second than the first bout, and the magnitude of the repeated bout effect was similar among the muscles. Plasma CK activity and Mb concentration did not increase significantly after the second exercise bout. It was concluded that muscle damage was greater for arm than leg muscles, and muscle proteins in the blood increased to a critical level after unaccustomed whole-body resistance exercises, but the magnitude of damage was largely attenuated for all muscles similarly after the second bout.

Using first bout effect to study the mechanisms underlying eccentric exercise induced force loss

INTRODUCTION

The first bout of eccentric exercise is known to have a protective effect on the consequent bouts. This effect is still disputable as it is not known whether it protects muscle damage by reducing force production or by improving force recovery in the healing process. The underlying mechanisms of this protective effect have not been fully understood.

OBJECTIVES

To determine the mechanisms of this protective effect, three different loads were used for the first eccentric bout. This was done to investigate whether the protective effect is related to the size of the load in the first bout. To determine the neural adaptations, voluntary activation was assessed and to determine the muscular adaptations, the resting twitch was measured.

METHOD

Thirty healthy participants were selectively allocated into three groups (low-, moderate- and high-load group) to match for maximal voluntary contraction (MVC) (n = 10 per group). Participants in each group performed only one of the three sets of ten eccentric (ECC) exercises of the elbow flexors (10%, 20% and 40% of MVC) as their first eccentric bout. The second bout of eccentric exercise was performed two weeks later and was identical for all the three groups, i.e., 40% ECC.

RESULTS

The results showed that for the first bout, MVC, voluntary activation and the resting twitch displayed significant (p < 0.0001) interaction (group x time). This was not the case however for the second bout as there was no significant (group x time) interaction in all outcome variables immediately after exercise. When the first and second bouts were compared, it was found that the high-load group had faster recovery in MVC at day 1 and 4 corresponding to voluntary activation and only at day 4 corresponding to the resting twitch.

CONCLUSIONS

In this study, it was found that high-load exercise aids fast recovery either via neural or muscular adaptations.

Contralateral Repeated Bout Effect of the Knee Flexors

PURPOSE

Eccentric exercise of the elbow flexors (EF) confers protective effect against muscle damage of the same exercise performed by the opposite arm at 1, 7, or 28 d later. This is known as the contralateral repeated bout effect (CL-RBE), but it is not known whether CL-RBE is evident for the knee flexors (KF). The present study tested the hypothesis that KF CL-RBE would be observed at 1, 7, and 28 d after the initial bout.

METHODS

Young untrained men were assigned to a control or one of three experimental groups (n = 13 per group). The experimental groups performed 60 maximal KF eccentric contractions (60MaxEC) using one leg followed by the same exercise using the opposite leg at 1, 7, or 28 d later. The control group used the nondominant leg to repeat 60MaxEC separated by 14 d. Changes in several indirect muscle damage markers after 60MaxEC were compared between bouts and among the groups by using a mixed-design, two-way ANOVA.

RESULTS

Changes in maximal voluntary isokinetic concentric contraction torque, range of motion, muscle soreness, and plasma creatine kinase activity after the first 60MaxEC were similar among the groups. These changes were smaller after the second than the first 60MaxEC for the control, 1-d, and 7-d groups, and the changes after the second 60MaxEC were smaller for the control than for both the 1- and 7-d groups (P < 0.05). When the KF CL-RBE was compared with the EF CL-RBE of the previous study, the magnitude was not significantly different.

CONCLUSIONS

These results showed that CL-RBE was evident for KF in a similar manner to that for EF, but did not last for 28 d, and the CL-RBE was smaller than the ipsilateral RBE.

Flavanol-Rich Cacao Mucilage Juice Enhances Recovery of Power but Not Strength from Intensive Exercise in Healthy, Young Men

(1) Background: Mucilage within cacao pods contains high levels of polyphenols. We investigated whether consumption of cacao juice enhances the recovery of muscle function following intensive knee extension exercise. (2) Methods: Ten recreationally active males completed two trials of 10 sets of 10 single leg knee extensions at ~80% one repetition maximum. Participants consumed each supplement (ZumoCacao^® juice, CJ or a dextrose drink, PL) for 7 days prior to and 48 h post exercise. Knee extension maximum voluntary contraction (MVC) and a counter movement jump (CMJ) were performed at baseline, immediately, 24 h, and 48 h post-exercise. Venous blood samples were collected at each time point and analyzed for indices of inflammation, oxidative damage, and muscle damage. (3) Results: CMJ height recovered faster with CJ at 24 h and 48 h post-exercise (p < 0.05), but there was no effect of CJ on recovery of MVC (both p > 0.05). There was also no effect of the trial on any blood markers (all p > 0.05). (4) Conclusions: Supplementation with CJ for 7 days prior to and 2 days after intensive knee extensor exercise improved functional recovery as shown by an improved recovery of CMJ up to 48 h post-exercise. However, the precise mechanism of action is unclear and requires further investigation.

Implications of Impaired Endurance Performance following Single Bouts of Resistance Training: An Alternate Concurrent Training Perspective

A single bout of resistance training induces residual fatigue, which may impair performance during subsequent endurance training if inadequate recovery is allowed. From a concurrent training standpoint, such carry-over effects of fatigue from a resistance training session may impair the quality of a subsequent endurance training session for several hours to days with inadequate recovery. The proposed mechanisms of this phenomenon include: (1) impaired neural recruitment patterns; (2) reduced movement efficiency due to alteration in kinematics during endurance exercise and increased energy expenditure; (3) increased muscle soreness; and (4) reduced muscle glycogen. If endurance training quality is consistently compromised during the course of a specific concurrent training program, optimal endurance development may be limited. Whilst the link between acute responses of training and subsequent training adaptation has not been fully established, there is some evidence suggesting that cumulative effects of fatigue may contribute to limiting optimal endurance development. Thus, the current review will (1) explore cross-sectional studies that have reported impaired endurance performance following a single, or multiple bouts, of resistance training; (2) identify the potential impact of fatigue on chronic endurance development; (3) describe the implications of fatigue on the quality of endurance training sessions during concurrent training, and (4) explain the mechanisms contributing to resistance training-induced attenuation on endurance performance from neurological, biomechanical and metabolic standpoints. Increasing the awareness of resistance training-induced fatigue may encourage coaches to consider modulating concurrent training variables (e.g., order of training mode, between-mode recovery period, training intensity, etc.) to limit the carry-over effects of fatigue from resistance to endurance training sessions.