Eccentric Muscle Contractions: Risks and Benefits

Impact of mild leg length discrepancy on pelvic alignment and gait compensation in children

BACKGROUND

Leg length discrepancy (LLD) is common in children and often leads to pelvic lateral tilt as a primary gait deviation. While children rarely report low back pain, prolonged LLD can induce lasting changes in lumbar spine biomechanics, potentially resulting in future back issues. To mitigate the effects of LLD, children often employ various compensatory mechanisms. However, the degree of LLD that significantly impacts gait remains unclear.

RESEARCH QUESTION

This study aims to identify gait deviations in children and adolescents with mild LLD and examine the relationship between LLD severity and lower limb compensatory strategies.

METHODS

Fifty-one children and adolescents (mean age 12.6 years, SD = 2.5) with mild LLD ranging from 0.0 to 3.0 cm were enrolled. Exclusion criteria included neurological involvement, scoliosis, syndromes, and lower extremity joint contractures. Pelvic motion and gait compensations were evaluated across three groups: LLD 0-1 cm, LLD 1-2 cm, LLD 2-3 cm Correlations between gait parameters and LLD were assessed.

RESULTS

Pelvic lateral tilt showed significant correlations with LLD severity. Kinematic analyses revealed significant joint adaptations on the long leg side, leading to functional shortening, particularly in the 2-3 cm group, which displayed multiple and clear compensations. Notably, only ankle dorsiflexion on the long side significantly correlated with LLD.

SIGNIFICANCE

In cases of mild LLD, pelvic adaptations include lateral tilt, counterbalanced by lowering the longer leg. In absence of ankle contractures, individuals tend to avoid lengthening the shorter leg through toe walking, as it requires greater muscular effort. These adaptive strategies correlate with LLD severity, suggesting that even mild discrepancies may contribute to overuse injuries affecting the spine and longer limb. This study highlights the importance of recognizing and addressing mild LLD in relation to symptoms associated with pelvic tilt and ankle issues on the long leg.

Effects of eccentric resistance training after stroke on body function, activities of daily living and cognitive function: A review

Impairments on body function, activities of daily living (ADL) and cognition are common after stroke. Eccentric resistance training (ERT) may be implemented to improve them. The primary objectives were to evaluate whether ERT improves body function, ADL and cognition after stroke. The secondary objectives were to evaluate whether ERT improves strength, gait, quality of life, and self-perceived health. Seven electronic databases were searched: Cochrane Central Register of Controlled Trials, Cochrane Stroke Group Trials Register, PubMed, Epistemonikos, Embase, SPORTDiscus, and WHO International Clinical Trials Registry Platform. Last search was run in December 2023, including studies since 2012. Selection criteria were studies with stroke participants of both sexes, aged 18 or more, with an intervention based on ERT. Accepted languages were English, Spanish or French. First search was done in pairs. Authors removed duplicate studies and those which did not meet inclusion criteria through title and abstracts. Finally, all authors, independently, screened the final search results and extracted data. Of 68 records identified, 15 were eligible and 6 were finally included (with moderate risk of bias), analyzing 159 participants. Body function (4 interventions, n ​= ​84), gait (4 interventions, n ​= ​115) and strength (3 interventions, n ​= ​78) showed significantly better results when ERT was performed. Meta-analysis could not be done because of the few studies and their heterogeneity. This review provided low-moderate quality evidence suggesting that ERT might be effective at improving body function, strength, and gait after stroke. Besides, no harm was documented, and it was well-accepted.

Objective measures of stiffness and ratings of pain and stiffness in the gastrocnemii following delayed-onset muscle soreness

BACKGROUND

Muscle stiffness is commonly associated with a sensation of tightness, pain and movement difficulty. It is unclear, however, whether changes in muscle stiffness can be objectively identified by myotonometry across time. This study investigated whether a myotonometer (MyotonPRO) can detect changes in muscle stiffness by delayed-onset muscle soreness (DOMS).

METHODS

Twenty-three healthy adults participated in this study. DOMS was achieved in the gastrocnemii by downhill-backwards walking on a motorised treadmill. Subjective ratings of gastrocnemii pain and stiffness were recorded using the numerical rating scale. The MyotonPRO was used to record and extract objective muscle stiffness data. Recordings were taken at baseline and over a three-week recovery period. Spearman's rho correlation analyses were conducted between objective measures and subjective ratings of pain and stiffness. Repeated measure ANOVA tests were conducted to investigate the effect of DOMS over time.

FINDINGS

No significant correlations were found between the objective measures and subjective ratings of pain (p = 0.22) or stiffness (p = 0.51). Myotonometry identified significant effects of DOMS on muscle stiffness (p < 0.001) over time. Significant effects of DOMS on subjective pain and stiffness rating data were found over time (p < 0.001).

INTERPRETATIONS

Although DOMS was found to affect objective measures of muscle stiffness, these changes were not associated with subjective ratings. Future studies could replicate this study using other myotonometry methods to further investigate muscle stiffness and involve a larger cohort. Other work should investigate muscle stiffness in clinical musculoskeletal conditions resulting from injury or chronic pain.

Peak Eccentric Cycling Exercise and Cardiorespiratory Responses to Normobaric Hypoxia Versus Normobaric Normoxia in Healthy Adults: A Randomized, Controlled Crossover Trial

Background/Objectives: Pulmonary rehabilitation clinics are traditionally located at higher altitudes (HAs), where lower PO2 reduces exercise capacity and blood oxygenation. Eccentric cycling exercise (ECC), with its lower cardiorespiratory demand compared to concentric cycling (CON), might therefore be a potential advantageous training modality at HAs, particularly for individuals with reduced exercise capacity. This study aimed to compare the cardiorespiratory responses of ECC while breathing normoxic versus hypoxic gas in healthy participants. Methods: This randomized, controlled crossover trial involved healthy participants performing CON in normoxia (FiO2 = 0.21), followed by two incremental ECC tests until 70-100% of peak exercise, one with normoxia and one with normobaric hypoxia (FiO2 = 0.15), in a randomized order. Oxygen uptake (V'O2) and additional outcomes were measured breath-by-breath. Endpoints were defined at rest, 50%, 70%, peak exercise, and isotime. The trial is registered on clinicaltrails.gov (NCT05185895). Results: Twelve healthy participants (age: 30 ± 11 years, six females) completed the study. During both interventions, V'O2 increased linearly with exercise intensity, with no significant differences between normoxic and hypoxic conditions. At peak exercise, SpO2 and peak work rate were significantly lowered by 5% (95%CI: 3 to 8%, p < 0.001) and by 22 W (95%CI: 8 to 36 W, p = 0.009) in hypoxia compared to normoxia. Other outcomes were unchanged. When comparing CON to ECC in normoxia, the mean differences in V'O2 increased with higher loads. Conclusions: This study demonstrated that V'O2 and other cardiopulmonary parameters remain unchanged when performing ECC in hypoxia compared to normoxia. Comparing CON to ECC in normoxia, participants achieved higher workloads and greater V'O2 consumption during CON compared to ECC at comparable watts, confirming the higher metabolic cost associated with CON. We identified that the optimal submaximal ECC intensities, with the highest difference in V'O2 between CON versus ECC, are around 40% of peak V'O2.

Neuromuscular and biochemical responses of the hamstrings to a Flywheel Russian belt Deadlift in women and men

The purpose of the study was to analyze hamstrings muscle damage and recovery after a novel Flywheel Russian belt Deadlift (FRBD) exercise using neuromuscular tests and associated biochemical markers of structural damage. Maximal voluntary isometric contraction (MVIC) torque and rate of force development (RFD) over several time-intervals by the 90ºhip:20ºknee test (standing isometric test for the hamstrings) and range of motion (ROM) Jurdan test (combination of active knee extension test and modified Thomas test), together with serum biomarkers of muscle damage and oxidative stress, were tested at baseline and  +24h,  +48h and  +72h in healthy, untrained and physically active 15 females (age= 21.5±3.4 years) and 15 males (age= 21.4±1.9 years). FRBD-induced muscle damage was observed as a reduction in MVIC torque and RFD at all time-intervals until +72h. Also, hamstrings neuromuscular capacity reductions were associated with serum biomarkers of structural and oxidative damage. However,  only males showed ROM changes. Overall, the FRBD triggered a decrease in hamstrings neuromuscular capacities, and an upregulation of biochemical markers of structural and oxidative damage until +72h. The 90ºhip:20ºknee test provides an adequate reliability to screen hamstrings recovery in both women and men after flywheel training, through MVIC torque and both early and late RFD.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Evaluation of curcumin intake in reducing exercise-induced muscle damage in athletes: a systematic review

BACKGROUND

Sports practice, particularly eccentric exercises, induces significant muscular changes, including muscle fiber injuries, strength loss, pain, and increased permeability of the muscle membrane. The duration of muscle recovery depends on factors such as exercise intensity and the specific muscle groups engaged. The inflammatory response plays a crucial role in muscle regeneration, involving various cell types. Curcumin, especially when its stability is enhanced through encapsulation, exhibits potent antioxidant and anti-inflammatory properties. Supplementing with curcumin can reduce muscle damage and inflammation caused by eccentric exercise, making it a potential remedy for athletes.

OBJECTIVE

The objective of this systematic review is to assess the scientific evidence supporting the efficacy of curcumin in reducing muscle damage caused by sports.

METHODS

A structured search in SCOPUS, Medline, and Web of Science databases was conducted in March 2023, including all available articles. The strategy involved selecting English articles without time constraints, using the search terms "curcumin" AND "Exercise-Induced Muscle Damage" (ALL(curcumin AND "Exercise-Induced Muscle Damage")). Titles and abstracts were screened to assess eligibility. Studies were chosen based on PICOS criteria, and quality was evaluated using the reliable PEDro scale. The eligibility criteria included adults without any diagnosed diseases who regularly exercise (at least three times per week) and follow a consistent pattern of curcumin intake before, during, or after exercise.

RESULTS

The comprehensive search identified 11 relevant studies investigating the effects of curcumin supplementation in sport-simulated interventions. These studies suggest that curcumin intake may help reduce muscle symptoms associated with eccentric exercises, thereby improving pain perception. Effective use of curcumin depends on factors such as dosage, bioavailability, and timing, with post-exercise ingestion appearing to be more beneficial.

CONCLUSIONS

Curcumin demonstrates a significant potential to relieve muscle-related symptoms, especially delayed-onset muscle soreness (DOMS) that arises from eccentric exercises, thus potentially improving the well-being of those who are trained. It also appears to have the capability to lower biomarkers associated with inflammation and boost antioxidant levels. Nevertheless, for future studies, the bioavailability of curcumin must be considered, as it is a key factor in its efficacy.

Forces experienced at different levels of the musculoskeletal system during horizontal decelerations

Horizontal decelerations are frequently performed during team sports and are closely linked to sports performance and injury. This study aims to provide a comprehensive description of the kinetic demands of decelerations at the whole-body, structural, and tissue-specific levels of the musculoskeletal system. Team-sports athletes performed maximal-effort horizontal decelerations whilst full-body kinematics and ground reaction forces (GRFs) were recorded. A musculoskeletal model was used to determine whole-body (GRFs), structural (ankle, knee, and hip joint moments and contact forces), and tissue (twelve lower-limb muscle forces) loads. External GRFs in this study, especially in the horizontal direction, were up to six times those experienced during accelerated or constant-speed running reported in the literature. To cope with these high external forces, large joint moments (hip immediately after touchdown; ankle and knee during mid and late stance) and contact forces (ankle, knee, hip immediately after touchdown) were observed. Furthermore, eccentric force requirements of the tibialis anterior, soleus, quadriceps, and gluteal muscles were particularly high. The presented loading patterns provide the first empirical explanations for why decelerating movements are amongst the most challenging in team sports and can help inform deceleration-specific training prescription to target horizontal deceleration performance, or fatigue and injury resistance in team-sports athletes.

Arginine ingestion inhibits phagocyte invasion in eccentrically contracted rat fast-twitch muscle

Eccentric contraction (ECC) has been shown to induce leukocyte invasion into skeletal muscle, resulting in muscle inflammation. This study aimed to investigate whether prior ingestion of L-arginine (ARG), a nitric oxide precursor, inhibits ECC-induced macrophage invasion. Male Wistar rats received ARG in water for 7 days, beginning 3 days prior to ECC. ECCs were induced in the anterior crural muscles for 200 cycles. Three days later, the tibialis anterior and extensor digitorum longus muscles were excised for biochemical analysis and force measurement, respectively. ARG ingestion increased nitrite and nitrate levels in plasma and muscle, inhibiting force depression and reducing CD68 content in muscles subjected to ECC. ARG ingestion also ameliorated an ECC-induced increase in protein nitration, although neither ARG ingestion nor ECC induction affected protein carbonyl levels. The present results suggest that ingestion of ARG or ARG-rich foods may alleviate inflammation by attenuating phagocyte invasion in eccentrically contracted skeletal muscles.

Advancements in Therapeutic Approaches for Degenerative Tendinopathy: Evaluating Efficacy and Challenges

Degenerative tendinopathy results from the accumulation of minor injuries following unsuccessful tendon repair during acute tendon injuries. The process of tendon repair is prolonged and varies between individuals, making it susceptible to reinjury. Moreover, treating chronic tendinopathy often requires expensive and extensive rehabilitation, along with a variety of combined therapies to facilitate recovery. This condition significantly affects the quality of life of affected individuals, underscoring the urgent need for more efficient and cost-effective treatment options. Although traditional treatments have improved significantly and are being used as substitutes for surgical interventions, the findings have been inconsistent and conflicting. This review aims to clarify these issues by exploring the strengths and limitations of current treatments as well as recent innovations in managing various forms of degenerative tendinopathy.

The importance of analysing a single common window of a concentric and eccentric dynamic muscle contraction: unveiling the components of EMG data and motor unit pool

This study proposes a method for analysing decomposed electromyographic signals to enhance the characterization of motor units (MU). It involves two steps: (i) clustering groups of motor units based on firing rate (FR), recruitment threshold, and MU action potential amplitude, and (ii) segmentation of data at the time of interest. Such method, capable of distinguishing different groups of MU, could help understanding muscle force production. FR of MU in Vastus Lateralis and Rectus Femoris during knee extension was investigated. The findings distinguish MU groups and reveals differences in: FR between both contractions types; clustered groups; and segmented MU data in both contraction types.

Delayed Recovery After Exercise-Induced Pain in People with Chronic Widespread Muscle Pain Related to Cortical Connectivity

BACKGROUND/OBJECTIVES

There is a subset of patients with pain who become worse after exercise. To explore this, we examined the responses of people with chronic primary pain to a standardized high intensity exercise protocol used to induce delayed onset muscle soreness (DOMS).

METHODS

Ten participants with a diagnosis of chronic widespread muscle pain (CWMP) were matched by age and reported gender to ten participants without muscle pain (i.e., no pain (NP)). Participants completed a standardized DOMS protocol. Pain intensity in the arm at rest and with movement was assessed using daily electronic diaries. Peak pain, the timing of peak pain, and the time to recovery were compared between groups. Associations of pain variables with the functional connectivity of the sensorimotor (SMN), cerebellum, frontoparietal control (FPN), and default mode network (DMN) both within network nodes and the rest of the brain was assessed.

RESULTS

Significant differences in peak pain, the time to peak pain, and the time to recovery were noted between groups for both pain at rest and pain with movement after controlling for catastrophizing and pain resilience. Connectivity across the SMN, FPN, and DMN was associated with all pain-related variables. Significant group differences were identified between groups.

CONCLUSIONS

A standardized muscle "injury" protocol resulted in more pain, a longer time to peak pain, and a longer time to resolve pain in the patient group compared to the NP group. These differences were associated with differences in connectivity across brain regions related to sensorimotor integration and appraisal. These findings provide preliminary evidence of the dysregulation of responses to muscle (micro)trauma in people with chronic pain.

Greater Neuromuscular and Perceptual Fatigue after Low versus High Loads in the Bench Press: A Preliminary Study Applying Frequentist and Bayesian Group Analyses with Subject-by-Subject Case Series Reports

Background/Objective: This study investigated the differences in acute fatigue following resistance training performed with low versus high loads in the bench press (BP). Methods: Trained males (n = 5, 21.2 ± 2.77 years; 81.86 ± 6.67 kg; 177 ± 7.52 cm) undertook three protocols with 50%RM and three with 85%RM with volume equalized between protocols: muscular failure protocols (TF, RTP1 and 2), half-maximum repetition protocols (RTP3 and 4), and cluster set protocols (RTP5 and 6). Mechanical performance, lactate, and perceptual responses were analyzed during protocols and at post 0, 24, and 48 h using frequentist (p < 0.05) and Bayesian approaches. Results: Moderate to large (ES ≥ 0.3) and trivial to moderate (ES < 0.3) effects were observed at 0 and 24 h post-session, respectively, across all protocols. TF protocols, particularly RTP1, showed the greatest impairments when compared to the other RTP (ES ≥ 0.3). The Bayesian analysis supported the frequentist results, showing strong-decisive evidence for our data under the model that included protocols as predictors for mechanical, metabolic, and perceptual variables during protocols. Inter-individual variability in responses was observed in the neuromuscular tests, potentially related to the strength level and perceptual responses. Conclusions: In summary, TF generates greater fatigue, while reducing set volume to half of maximum repetitions or including intra-set rest that helps to mitigate fatigue symptoms.

The effects of the addition of Mulligan mobilization with movement to exercise on elbow pain and function associated with lateral elbow tendinopathy

BACKGROUND

Mulligan mobilization with movement (MWM) and eccentric exercise (EE) have been shown to be effective for the treatment of chronic lateral elbow tendinopathy (LET). However, the addition of MWM to EE effects on LET remained unknown. The objective of the study was to determine the effects of adding of Mulligan mobilization with movement to eccentric exercise for the treatment of LET.

METHODS

In this quasi-experimental study, thirty participants with unilateral LET were assigned into two groups: 15 in MWM (received MWM + EE) (7 M and 8 F, mean age 36.8 ± 8.3 years) and 15 in EE (9 M and 6 F, mean age 46 ± 8.1 years). Both groups received education about painful activities and eccentric exercise, while the MWM group received MWM with the same eccentric exercise as the EE group. The visual analog scale (VAS) and the patient-rated tennis elbow evaluation (PRTEE) were used to assess pain and upper limb function, respectively, at baseline and at the end of 4 weeks. The data was analyzed using an independent t-test and a paired t-test.

RESULTS

There was no significant difference (p > 0.05) between groups at baseline. At the end of 4 weeks, significant and clinically meaningful improvements in pain and function were observed for both groups (p < 0.001); however, MWM group showed much better results in VAS (p < 0.001, d = 1.3) and PRTEE (p < 0.001, d = 5.2) CONCLUSION: This study showed that adding MWM to eccentric exercise resulted in enhanced pain reduction and improved function of the upper limb.

Effects of eccentric strength training on motor function in individuals with stroke: a scoping review

BACKGROUND

Preliminary evidence suggests that eccentric strength training (ECC) improves muscle strength and postural control in individuals with stroke; however, the evidence about the effects of ECC in people living with stroke has not been systematically analyzed.

OBJECTIVE

To determine the effects of ECC, compared to other exercise modalities (i.e., concentric training), on motor function in individuals with stroke.

METHODS

This scoping review was performed according to PRISMA extension for scoping reviews. Until March 2023, a comprehensive search of studies using ECC intervention to improve motor functions in individuals with stroke was performed. Study designs included were randomized and non-randomized controlled trials and quasi-experimental studies using MEDLINE, Web of Science, Rehabilitation & Sports Medicine, PEDro, and OTSeeker databases. Two independent reviewers selected articles based on title and abstract and extracted relevant information from the eligible studies. The results were qualitatively synthesized, and the critical appraisal was performed using the Rob 2.0 and Robins-I tools.

RESULTS

Ten studies, with 257 individuals, were analyzed. ECC revealed positive effects on muscle strength, muscular activity, balance, gait speed, and functionality, mainly compared with concentric training, physical therapy, and daily routine. No significant adverse events were reported during ECC. The critical appraisal of individual articles ranged from some to high concern.

CONCLUSION

ECC had a greater and positive effect on motor function in individuals with stroke than other exercise modalities. However, the limited number of studies, variability of outcomes, and the risk of bias produced a low certainty of evidence.

Impact of lengthening velocity on the generation of eccentric force by slow-twitch muscle fibers in long stretches

After an initial increase, isovelocity elongation of a muscle fiber can lead to diminishing (referred to as Give in the literature) and subsequently increasing force. How the stretch velocity affects this behavior in slow-twitch fibers remains largely unexplored. Here, we stretched fully activated individual rat soleus muscle fibers from 0.85 to 1.3 optimal fiber length at stretch velocities of 0.01, 0.1, and 1 maximum shortening velocity, vmax, and compared the results with those of rat EDL fast-twitch fibers obtained in similar experimental conditions. In soleus muscle fibers, Give was 7%, 18%, and 44% of maximum isometric force for 0.01, 0.1, and 1 vmax, respectively. As in EDL fibers, the force increased nearly linearly in the second half of the stretch, although the number of crossbridges decreased, and its slope increased with stretch velocity. Our findings are consistent with the concept of a forceful detachment and subsequent crossbridge reattachment in the stretch's first phase and a strong viscoelastic titin contribution to fiber force in the second phase of the stretch. Interestingly, we found interaction effects of stretch velocity and fiber type on force parameters in both stretch phases, hinting at fiber type-specific differences in crossbridge and titin contributions to eccentric force. Whether fiber type-specific combined XB and non-XB models can explain these effects or if they hint at some not fully understood properties of muscle contraction remains to be shown. These results may stimulate new optimization perspectives in sports training and provide a better understanding of structure-function relations of muscle proteins.

Home care program and exercise prescription for improving quality of life in geriatric population with knee osteoarthritis: A systematic review and meta-analysis

BACKGROUND

Knee Osteoarthritis (OA) is a degenerative bone disease commonly affecting the elderly. Exercise has emerged as a primary treatment strategy for individuals with knee OA. Various exercise regimes are now recognized as key approaches in managing OA.

OBJECTIVE

To evaluate the impact of a Home Care program combined with Exercise prescriptions on the quality of life in the geriatric population with knee OA.

METHODS AND MATERIALS

This review was conducted following a systematic approach to search for relevant articles in electronic databases. Studies published between 2011 and 2021 were included, following the PRISMA Guidelines. The databases screened included PubMed, Scopus, Cochrane, PEDro, MEDLINE, and EMBASE, using medical subject headings (MeSH) and Health Science Description (DeSC) terms.

RESULTS

A total of 12 studies involving participants undergoing home care programs and exercise prescriptions for OA were identified. The review findings indicated significant improvements in pain management and quality of life for individuals adhering to a structured home care program and therapist-guided exercise prescription.

CONCLUSION

The review suggests that implementing a home care program alongside an appropriate exercise regimen can enhance the quality of life in geriatric patients with knee OA, improving adherence to physical activity and overall patient outcomes.

Preventive effect of foam rolling on muscle soreness after exercise: A systematic review and meta-analysis

OBJECTIVE

This systematic review and meta-analysis aimed to evaluate the effect of foam rolling (FR) on exercise-induced muscle soreness.

METHODS

PubMed, EMBASE, Web of Science, ProQuest, Cochrane Library and China National Knowledge databases were searched to identify randomized controlled trials (RCTs) of the effect of FR intervening muscle soreness after exercise, from their inception to August 2022. The outcome indicators were visual analogue scale (VAS) and pressure-pain threshold (PPT).

RESULTS

A total of 16 studies were included, involving 515 subjects. Meta-analysis results show that FR has a certain effect of elimination of muscle soreness after exercise. The standard mean deviation (SMD) and 95% confidence interval (95%CI) of VAS and PPT immediately after intervention, 24, 48 and 72 h: [SMD = -0.38, 95%CI (-0.61, -0.15), P = 0.001], [SMD = -0.53, 95%CI (-0.82, -0.25), P = 0.0003], [SMD = -0.77, 95%CI (-1.12, -0.42), P < 0.00001], [SMD = -0.67, 95%CI (-1.09, -0.24), P = 0.002], [SMD = 0.23, 95%CI (0.62, 0.16), P = 0.25], [SMD = 0.48, 95%CI (0.11, 1.07), P = 0.11], [SMD = 0.39, 95%CI (-0.24, 1.02), P = 0.22], [SMD = 0.37, 95%CI (0.01, 0.74), P = 0.04].

CONCLUSION

Using foam rolling after exercise has a certain preventive effect on muscle soreness. Our study found that the effect of intervention of FR immediately is tiny after exercise, while the effective of intervening is relative obvious above 24 h.

REGISTRATION

PROSPERO (registration number: CRD42021250174).

Impact of eccentric cycling in coronary rehabilitation program: a pragmatic randomized controlled trial versus conventional rehabilitation

BACKGROUND

This randomized controlled trial examined the feasibility of adding eccentric exercise to a conventional cardiac rehabilitation program (CCRP) for coronary heart disease patients.

METHODS

Ninety-three patients were randomly assigned to either the MIX group (eccentric ergometer + CCRP) or the CON group (concentric ergometer + CCRP) for 7 weeks. Training effectiveness was assessed based on "good responders" showing improved functional capacities, such as 6-minute walk test (6MWT) distance and maximal voluntary contraction of the plantar flexors (ankle MVC). Safety was monitored with a visual analog scale for muscle soreness, perceived exertion, and heart rate during training.

RESULTS

The proportion of good responders was similar between groups (26% in MIX, 29% in CON, P=0.744). Both groups improved in 6MWT (CON: 12.6%, MIX: 16.14%) and ankle MVC (CON: 15.5%, MIX: 11.30%), with no significant differences. Exercise tolerance did not differ significantly between the groups, but perceived effort was significantly lower in the MIX group (P<0.0001) compared to the CON group.

CONCLUSIONS

Integrating eccentric exercise into cardiac rehabilitation is safe and well-tolerated. Nevertheless, this study did not find significant advantages over conventional programs for coronary heart disease patients. Further research should explore specific patient groups or conditions where eccentric exercise may be more beneficial, emphasizing personalized prescriptions and gradual workload progression for better cardiac rehabilitation outcomes.

Cross-education of lower limb muscle strength following resistance exercise training in males and females: A systematic review and meta-analysis

Cross-education describes the training of one limb that leads to performance enhancements in the contralateral untrained limb, driven by neural changes rather than muscle adaptation. In this systematic review and meta-analysis, we aimed to evaluate the efficacy of cross-education (vs. a control group) via resistance exercise training (RET) for improving muscle strength in the untrained lower limb of healthy males and females. A literature search from inception to September 2023 was conducted using MEDLINE (via PubMed), the Cochrane Library (CENTRAL), Web of Science (Core Database), Scopus, EBSCO-host, and Ovid-EMBASE. Independent screening, data extraction and quality assessment were conducted. The measured outcomes were change in one-repetition maximum (1-RM) load, maximum voluntary contraction (MVC), and concentric, eccentric and isometric peak torque. Change in muscle structure (pennation angle and muscle thickness) was also analysed. A total of 29 studies were included. The pooled effect size from the random-effects model shows that cross-education significantly increased 1-RM compared to the control group (standardised mean difference (SMD): 0.59, 95% CI: 0.22-0.97; P = 0.002). Cross-education also significantly improved MVC (SMD: 0.55, 95% CI: 0.16-0.94; P = 0.006), concentric (SMD: 0.61, 95% CI: 0.39-0.84; P < 0.00001), eccentric (SMD: 0.39, 95% CI: 0.13-0.64; P = 0.003) and isometric (SMD: 0.45, 95% CI: 0.26-0.64; P < 0.00001) peak torque, each compared to the control group. When RET was categorised as eccentric or concentric, subgroup analysis showed that only eccentric training was associated with significantly increased isometric peak torque via cross-education (SMD: 0.37, 95% CI: 0.13-0.61; P = 0.003) (concentric, SMD: 0.33, 95% CI: -0.09 to 0.74; P = 0.12). This systematic review and meta-analysis emphasise the potency of cross-education for improving lower limb muscle strength. These findings have potential implications for clinical situations of impaired unilateral limb function (e.g., limb-casting or stroke). Future work exploring the mechanisms facilitating these enhancements will help to develop optimised rehabilitation protocols.

Accentuated eccentric resistance training: Effects on physical performance in male and female athletes

This study aimed to compare the effects of an accentuated eccentric training programme on physical performance between men and women. Distributed in two groups by gender, 21 male and 21 female athletes performed four sets of seven repetitions of the half-squat exercise twice per week for 6 weeks. Both groups lifted the same absolute load using a rotary inertial device. To accentuate the eccentric action, the eccentric load was twice as heavy as the concentric load. Vertical jump, sprint, and change of direction (COD) performances were measured pre- and post-intervention. To measure strength gains, vertical ground reaction forces were measured for each repetition of the entire training programme. Vertical jump improved post-intervention (MG: 33.88 ± 4.94 to 35.41 ± 4.86; FG: 20.60 ± 4.62 to 22.12 ± 4.32; p < 0.001; η2p = 0.42), while sprint (MG: 3.08 ± 0.11 to 3.07 ± 0.13; FG: 3.66 ± 0.23 to 3.64 ± 0.23) and COD (MG: 7.77 ± 0.42 to 7.61 ± 0.47; FG: 8.44 ± 0.58 to 8.38 ± 0.57) remained unchanged. Concentric and eccentric forces increased for both groups from session 1 to 4 (p < 0.001; η2p >0.39), while only peak eccentric forces increased until session 12 (p = 0.009; η2p = 0.21). In conclusion, even when men are able to produce greater forces with similar loads, accentuated eccentric RT produces similar strength and strength-related adaptations in male and female athletes.

Temporal tracking of cysteine 34 oxidation of plasma albumin as a biomarker of muscle damage following a bout of eccentric exercise

PURPOSE

Exercise-induced muscle damage (EIMD) results in the generation of reactive oxygen species (ROS), but little is known about the temporal profile of change in ROS post-EIMD and how ROS levels relate to the onset of and recovery from EIMD. Our primary aim was to examine the effect of EIMD on the pattern of change in the blood level of thiol-oxidised albumin, a marker of oxidative stress.

METHODS

Seven male participants were subjected on separate days to eccentric muscle contraction to cause EIMD or a no-exercise condition. After each session, the participants collected daily dried blood spots to measure thiol-oxidised albumin and returned to the laboratory every 2 days for the assessment of indirect markers of EIMD, namely maximal voluntary contraction (MVC), delayed onset muscle soreness (DOMS), creatine kinase (CK), and myoglobin.

RESULTS

Eccentric exercise resulted in a significant decrease in MVC and increase in DOMS, CK, myoglobin, and thiol-oxidised albumin with the latter reaching above baseline level within 24-48 h post-exercise. All the markers of EIMD returned to baseline level within 6 days post-exercise, but not the level of thiol-oxidised albumin which remained elevated for 10 days after exercise. There was a moderate correlation between changes in thiol-oxidised albumin and DOMS, but no significant relationship between any other markers of muscle damage.

CONCLUSION

The levels of thiol-oxidised albumin increase in response to EIMD and remain elevated for several days post-exercise. The temporal pattern of change in the level of thiol-oxidised albumin suggests that this may be a useful biomarker of muscle repair post-EIMD.

Temporal expression of mitochondrial life cycle markers during acute and chronic overload of rat plantaris muscles

Skeletal muscle hypertrophy is generally associated with a fast-to-slow phenotypic adaptation in both human and rodent models. Paradoxically, this phenotypic shift is not paralleled by a concomitant increase in mitochondrial content and aerobic markers that would be expected to accompany a slow muscle phenotype. To understand the temporal response of the mitochondrial life cycle (i.e., biogenesis, oxidative phosphorylation, fission/fusion, and mitophagy/autophagy) to hypertrophic stimuli, in this study, we used the functional overload (FO) model in adult female rats and examined the plantaris muscle responses at 1 and 10 weeks. As expected, the absolute plantaris muscle mass increased by ∼12 and 26% at 1 and 10 weeks following the FO procedure, respectively. Myosin heavy-chain isoform types I and IIa significantly increased by 116% and 17%, respectively, in 10-week FO plantaris muscles. Although there was a general increase in protein markers associated with mitochondrial biogenesis in acute FO muscles, this response was unexpectedly sustained under 10-week FO conditions after muscle hypertrophy begins to plateau. Furthermore, the early increase in mito/autophagy markers observed under acute FO conditions was normalized by 10 weeks, suggesting a cellular environment favoring mitochondrial biogenesis to accommodate the aerobic demands of the plantaris muscle. We also observed a significant increase in the expression of mitochondrial-, but not nuclear-, encoded oxidative phosphorylation (OXPHOS) proteins and peptides (i.e., humanin and MOTS-c) under chronic, but not acute, FO conditions. Taken together, the temporal response of markers related to the mitochondrial life cycle indicates a pattern of promoting biogenesis and mitochondrial protein expression to support the energy demands and/or enhanced neural recruitment of chronically overloaded skeletal muscle.

Eccentric exercise-induced delayed onset trunk muscle soreness alters high-density surface EMG-torque relationships and lumbar kinematics

We aimed to assess high-density surface electromyography (HDsEMG)-torque relationships in the presence of delayed onset trunk muscle soreness (DOMS) and the effect of these relationships on torque steadiness (TS) and lumbar movement during concentric/eccentric submaximal trunk extension contractions. Twenty healthy individuals attended three laboratory sessions (24 h apart). HDsEMG signals were recorded unilaterally from the thoracolumbar erector spinae with two 64-electrode grids. HDsEMG-torque signal relationships were explored via coherence (0-5 Hz) and cross-correlation analyses. Principal component analysis was used for HDsEMG-data dimensionality reduction and improvement of HDsEMG-torque-based estimations. DOMS did not reduce either concentric or eccentric trunk extensor muscle strength. However, in the presence of DOMS, improved TS, alongside an altered HDsEMG-torque relationship and kinematic changes were observed, in a contraction-dependent manner. For eccentric trunk extension, improved TS was observed, with greater lumbar flexion movement and a reduction in δ-band HDsEMG-torque coherence and cross-correlation. For concentric trunk extensions, TS improvements were observed alongside reduced thoracolumbar sagittal movement. DOMS does not seem to impair the ability to control trunk muscle force, however, perceived soreness induced changes in lumbar movement and muscle recruitment strategies, which could alter motor performance if the exposure to pain is maintained in the long term.

MR elastography-based slip interface imaging (SII) for functional assessment of myofascial interfaces: A feasibility study

PURPOSE

Abnormal adherence at functional myofascial interfaces is hypothesized as an important phenomenon in myofascial pain syndrome. This study aimed to investigate the feasibility of MR elastography (MRE)-based slip interface imaging (SII) to visualize and assess myofascial mobility in healthy volunteers.

METHODS

SII was used to assess local shear strain at functional myofascial interfaces in the flexor digitorum profundus (FDP) and thighs. In the FDP, MRE was performed at 90 Hz vibration to each index, middle, ring, and little finger. Two thigh MRE scans were performed at 40 Hz with knees flexed and extended. The normalized octahedral shear strain (NOSS) maps were calculated to visualize myofascial slip interfaces. The entropy of the probability distribution of the gradient NOSS was computed for the two knee positions at the intermuscular interface between vastus lateralis and vastus intermedius, around rectus femoris, and between vastus intermedius and vastus medialis.

RESULTS

NOSS map depicted distinct functional slip interfaces in the FDP for each finger. Compared to knee flexion, clearer slip interfaces and larger gradient NOSS entropy at the vastus lateralis-vastus intermedius interface were observed during knee extension, where the quadriceps are not passively stretched. This suggests the optimal position for using SII to visualize myofascial slip interface in skeletal muscles is when muscles are not subjected to any additional force.

CONCLUSION

The study demonstrated that MRE-based SII can visualize and assess myofascial interface mobility in extremities. The results provide a foundation for investigating the hypothesis that myofascial pain syndrome is characterized by changes in the mobility of myofascial interfaces.

No immediate change in systemic cytokines following an eccentric muscle training session in people with multiple sclerosis

Background

Eccentric muscle contractions elicit distinct physiological responses, including modulation of the cytokine profile. Although relevant for rehabilitation, the effect of eccentric muscle training on the immune system has never been investigated in multiple sclerosis (MS).

Objectives

Examine the immediate cytokine response of interleukin-4 (IL-4), IL-6, IL-10, IL-17a, interferon-gamma, and tumor necrosis factor-alpha after a moderate eccentric training session in individuals with MS. Additionally, further investigate the association between systemic cytokine levels at rest and clinical measures of mobility and lower limb functional strength.

Design

Observational study.

Methods

The first session included blood sampling for baseline cytokine measures. Subsequently, the participant completed a battery of clinical assessments related to mobility and lower limb strength, that is, the Timed-Up-and-Go Test, Five-Repetition-Sit-to-Stand-Test (5STS), Four-Square-Step-Test, and Two-Minute-Walk-Test. The second session included the eccentric exercise training session, followed by a second blood sampling to assess the acute cytokine response to the eccentric training bout. This session comprised 10 exercises concentrating on the strength of the trunk and lower extremities.

Results

Twenty-seven people with MS (pwMS), with a mean age of 40.1 years, participated in the study. No difference was demonstrated in the cytokine concentration values between baseline and immediately after the eccentric training session. The 5STS explained 30.3% of the variance associated with interferon-gamma, 14.8% with IL-4, and 13.8% with IL-10.

Conclusion

An eccentric training bout does not impact cytokine concentration in the blood and, consequently, does not boost a pro-inflammatory response, thus, it can be performed on pwMS in a rehabilitation setting.

Comparing the Effect of Isoinertial Flywheel Training and Traditional Resistance Training on Maximal Strength and Muscle Power in Healthy People: A Systematic Review and Meta-Analysis

BACKGROUND

This systematic review and meta-analysis aimed to analyze whether isoinertial flywheel training (FWT) is superior to traditional resistance training (TRT) in enhancing maximal strength and muscle power in healthy individuals.

METHODS

Electronic searches were conducted in the Web of Science, PubMed, Cochrane Library, SPORTDiscus, and Scopus databases up to 21 April 2024. Outcomes were analyzed as continuous variables using either a random or fixed effects model to calculate the standardized mean difference (SMD) and 95% confidence intervals (CI).

RESULTS

A total of sixteen articles, involving 341 subjects, met the inclusion criteria and were included in the statistical analyses. The pooled results indicate no statistically significant differences between FWT and TRT in developing maximal strength in healthy individuals (SMD = 0.24, 95% CI [-0.26, 0.74], p = 0.35). Additionally, the pooled outcomes showed a small-sized effect in muscle power with FWT (SMD = 0.47, 95% CI [0.10, 0.84]), which was significantly higher than that with TRT (p = 0.01) in healthy individuals. Subgroup analysis revealed that when the total number of FWT sessions is between 12 and 18 (1-3 times per week), it significantly improves muscle power (SMD = 0.61, 95% CI [0.12, 1.09]). Significant effects favoring FWT for muscle power were observed in both well-trained (SMD = 0.58, 95% CI [0.04, 1.13]) and untrained individuals (SMD = 1.40, 95% CI [0.23, 2.57]). In terms of exercise, performing flywheel training with squat and lunge exercises significantly enhances muscle power (SMD = 0.43; 95% CI: 0.02-0.84, and p = 0.04). Interestingly, FWT was superior to weight stack resistance training (SMD = 0.61, 95% CI [0.21, 1.00]) in enhancing muscle power, while no significant differences were found compared to barbell free weights training (SMD = 0.36, 95% CI [-0.22, 0.94]).

CONCLUSIONS

This meta-analysis confirms the superiority of FWT compared to TRT in promoting muscle power in both healthy untrained and well-trained individuals. Squats and lunges for FWT are more suitable for improving lower limb explosive power. It is recommended that coaches and trainers implement FWT for six weeks, 2-3 times per week, with at least a 48 h interval between each session. Although FWT is not superior to free weights training, it is advisable to include FWT in sport periodization to diversify the training stimuli for healthy individuals.

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

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

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

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

Study on Anti-Inflammatory Effects of and Muscle Recovery Associated with Transdermal Delivery of Chaenomeles speciosa Extracts Using Supersonic Atomizer on Rat Model

Repetitive motion or exercise is associated with oxidative stress and muscle inflammation, which can lead to declining grip strength and muscle damage. Oleanolic acid and ursolic acid have anti-inflammatory and antioxidant properties and can be extracted from Chaenomeles speciosa through ultrasonic sonication. We investigated the association between grip strength declines and muscle damage induced by lambda carrageenan (LC) injection and exercise exposure in rats. We also assessed the reparative effects of transdermal pretreatment and post-treatment with C. speciosa extracts (CSEs) by using a supersonic atomizer. The half-maximal inhibitory concentration (IC50) of CSEs for cells was 10.5 mg/mL. CSEs significantly reduced the generation of reactive oxygen species and inflammatory factors (interleukin [IL]-6 and IL-1β) in in vitro cell tests. Rats subjected to LC injection and 6 weeks of exercise exhibited significantly increased inflammatory cytokine levels (IL-1β, TNF-α, and IL-6). Hematoxylin and eosin staining revealed inflammatory cell infiltration and evident muscle damage in the gastrocnemius muscle, which exhibited splitting and the appearance of the endomysium and perimysium. The treated rats' grip strength significantly declined. Following treatment with CSEs, the damaged muscles exhibited decreased IL-1β, TNF-α, and IL-6 levels and normal morphologies. Moreover, grip strength significantly recovered. Pretreatment with CSEs yielded an immediate and significant increase in grip strength, with an increase of 180% and 165% occurring in the rats exposed to LC injection and exercise within the initial 12 h period, respectively, compared with the control group. Pretreatment with CSEs delivered transdermally using a supersonic atomizer may have applications in sports medicine and training or competitions.

Engineering interfacial tissues: The myotendinous junction

The myotendinous junction (MTJ) is the interface connecting skeletal muscle and tendon tissues. This specialized region represents the bridge that facilitates the transmission of contractile forces from muscle to tendon, and ultimately the skeletal system for the creation of movement. MTJs are, therefore, subject to high stress concentrations, rendering them susceptible to severe, life-altering injuries. Despite the scarcity of knowledge obtained from MTJ formation during embryogenesis, several attempts have been made to engineer this complex interfacial tissue. These attempts, however, fail to achieve the level of maturity and mechanical complexity required for in vivo transplantation. This review summarizes the strategies taken to engineer the MTJ, with an emphasis on how transitioning from static to mechanically inducive dynamic cultures may assist in achieving myotendinous maturity.

Periscapular Strength Profile Changes in Collegiate Baseball Pitchers Over the Course of a Season

Background

Repetitive application of high forces to the shoulder and scapular musculature during the pitching motion over the course of a collegiate baseball season may lead to changes in strength and increased fatigue, potentially predisposing pitching athletes to injury. The purpose of this study was to investigate periscapular strength profiles of Division I collegiate baseball players over the course of a season.

Methods

This study was a retrospective data analysis of 18 Division I baseball pitchers. Isometric scapular plane abduction (scaption), external rotator, internal rotator, middle trapezius, and lower trapezius isometric strength was measured on throwing arm of each subject using a MicroFET 2 handheld dynamometer. Data were collected in a single session at the preseason, midseason, and postseason of the college baseball season, which spanned a five-month period. A repeated measures ANOVA was utilized to determine if there was a significant change in periscapular strength across the baseball season.

Results

Over the three time-points, all strength values decreased for each muscle group, with decreases ranging from 3-14%. Changes in scaption strength values were statistically significant (p=0.018, partial eta squared =0.284) with an 8% reduction over the entire season, specifically with a 5% decline from mid-season to post-season. While external rotator, internal rotator, middle trapezius, and lower trapezius strength values all decreased over the course of the season (range 0.02kg to 1.8kg), these differences were not statistically significant. However, the middle trapezius strength value change (1.3kg loss) exceeded the minimal detectible change.

Conclusion

Periscapular muscles in baseball pitchers diminish in strength over the course of a collegiate baseball season. Understanding strength changes over the course of a season may influence training and therapeutic interventions.

Level of Evidence

3b.

Acute patellar dislocation during isokinetic knee strength testing: A case report

Key Clinical Message

Isokinetic testing is a maximal muscle strength test which requires adequate patient's preparation and observer's care. While the available data suggests that isokinetic devices are safe, their use may rarely cause severe injuries. The screening of predisposing anatomical factors could help preventing injuries before testing.

Abstract

A 29-year-old athletic man presented an acute patellar dislocation on a healthy right knee during isokinetic muscle strength testing, which was conducted in the setting of an intensive physical rehabilitation program, for persistent left knee pain after arthroscopic surgery for meniscal tear. This is the first case to occur in an adult male without clear risk factors such as patellar dysplasia. Predisposing factors may include slightly elevated patellar tilt and lateral shift compared to the contralateral knee (researched from subsequent review of pre-injury X-rays), and an elevated quadricipital strength in the context of recreational bodybuilding. The dislocation occurred during eccentric extension phase of testing. Medial patellofemoral ligament reconstruction was conducted 6 months later. Isokinetic muscle strength testing is generally considered as a safe method, despite limited data on the devices' safety. Since severe injuries might rarely occur, adequate patient preparation is needed, as well as the screening of predisposing factors.

Recovery of spatio-temporal gait and functional parameters following unilateral eccentric exercise-induced muscle damage in the hamstrings

OBJECTIVES

This study aimed to analyze how spatiotemporal gait parameters, active knee extension range of motion, muscle activity, and self-perceived function change over a seven-day period in healthy individuals after exercise-induced muscle damage (EIMD) in the hamstrings.

DESIGN

Longitudinal cohort study.

METHODS

Twenty-four healthy males participated in four sessions before and after EIMD (pre-EIMD, 48 h, 96 h, and 168 h post-EIMD). A single-leg deadlift exercise was performed to provoke EIMD in the hamstrings of the dominant leg. Lower limb function perception, spatiotemporal gait parameters, active knee extension range of motion, and electromyographic (EMG) activity of the semitendinosus and biceps femoris muscles during gait and maximal isometric contraction were assessed bilaterally.

RESULTS

At 48 h, the EIMD-side showed reduced step length, active knee extension range of motion, maximal strength and EMG activity compared to baseline (P < 0.042), while increased relative EMG activity in the biceps femoris during gait (P = 0.001). At 96 h, step length and EMG activity on the EIMD-side reached similar values to those at baseline, whereas lower limb function perception and active knee extension range of motion returned to baseline state at 168 h post-EIMD. No changes over time were observed on the control-side.

CONCLUSIONS

Recovery from EIMD requires a multimodal assessment since the different parameters affected by EIMD recover at different paces. Active range of motion appears to be the last variable to fully recover. Self-perceived function should not be considered in isolation as it does not represent complete functional recovery.

Vitamin E Does not Favor Recovery After Exercises: Systematic Review and Meta-analysis

This review aimed to verify the effects of vitamin E supplementation on oxidative stress, inflammatory response, muscle damage, soreness, and strength in healthy adults after exercise. We searched the MEDLINE, EMBASE, SPORTDiscus, Cochrane CENTRAL, and Web of Science from inception to August 2023, with no language restrictions. We included randomized placebo-controlled trials evaluating the supplementation of vitamin E on the abovementioned outcomes after a bout of physical exercise in healthy participants (no restriction for publication year or language). Meta-analyses were conducted to compare vitamin E and placebo supplementations to obtain a 95% confidence interval (95%IC). Twenty studies were included (n=298 participants). The effect of supplementation was assessed between 0 h and 96 h after the exercise. Compared to placebo, vitamin E had no effects on lipid (95%IC= -0.09 to 0.42), protein (-2.44 to 3.11), SOD (-1.05 to 0.23), interleukin-6 (-0.18 to 1.16), creatine kinase (-0.33 to 0.27), muscle soreness (-1.92 to 0.69), and muscle strength (-1.07 to 0.34). Heterogeneity for the analyses on carbonyls, interleukin-6 (1 h and 3 h), and muscle soreness ranged between 70 to 94%. Supplementing with vitamin E should not be recommended to support the recovery process in healthy individuals after exercise, given the lack of efficacy in the analyzed variables following an exercise session.

Effects of once- versus twice-weekly eccentric resistance training on muscular function and structure in older adults: a randomised controlled trial

Adherence rates to current twice-weekly strength training guidelines are poor among older adults. Eccentric-only training elicits substantial improvements in muscle function/size so the aim of this study was to compare the effects of once- versus twice-weekly eccentric training programmes on muscle function/size in older adults. Thirty-six participants (69.4 ± 6.0 yr) were randomised into non-active control, once-, or twice-weekly training groups. Lower-limb muscle power, strength, and size were assessed at baseline, mid-, and post-eccentric training. Training was performed for 12 min per session at 50% of maximum eccentric strength. Significant increases in power (13%), isometric (17-36%) and eccentric (40-50%) strength, and VL muscle thickness (9-18%) occurred in both training groups following 12 weeks. Minimal muscle soreness was induced throughout the 12 weeks and perceived exertion was consistently lower in the twice-weekly training group. One weekly submaximal eccentric resistance training session over 12 weeks elicits similar improvements in neuromuscular function compared to the currently recommended twice-weekly training dose. Given the substantial improvements in neuromuscular function and previously reported low adherence to current twice-weekly training guidelines, eccentric training may be pivotal to developing a minimal-dose strategy to counteract neuromuscular decline. The trial was registered retrospectively on 24/01/2024 with ISRCTN (trial registration number: ISRCTN68730580).

Scapular Motor Control and Upper Limb Movement Quality in Subjects with and without Chronic Shoulder Pain: A Cross-Sectional Study

Despite the existence of several studies about the scapula’s position and motion, in shoulder pain conditions, there are still conflicting findings regarding scapular adaptations and reduced research about the scapula’s role during functional tasks. The present study aimed to compare scapular-related kinematic and electromyographic outcomes during different shoulder movements (with and without load) and the drinking task, between symptomatic and asymptomatic subjects. Forty subjects (divided into two groups) participated in this cross-sectional observational study. Scapulothoracic motion, scapulohumeral rhythm, and movement quality (considering trunk compensation, time-to-peak acceleration, and smoothness), as well as the relative surface electromyographic activity and muscle ratio considering the trapezius, serratus anterior, and levator scapulae (LS), were assessed. The symptomatic group presented the following: (1) changes in scapular upward rotation (p = 0.008) and winging (p = 0.026 and p = 0.005) during backward transport and drink phases; (2) increased muscle activity level of the middle trapezius (MT) in all tasks (p < 0.0001 to p = 0.039), of LS during shoulder elevation with load (p = 0.007), and of LS and LT during most of the drinking task phases (p = 0.007 to p = 0.043 and p < 0.0001 to p = 0.014, respectively); (3) a decreased serratus anterior lower portion activity level (SAlow) during shoulder lowering with load (p = 0.030) and drink phase (p = 0.047); and (4) an increased muscular ratio between scapular abductors/adductors (p = 0.005 to p = 0.036) and elevators/depressors (p = 0.008 to p = 0.028). Compared to asymptomatic subjects, subjects with chronic shoulder pain presented scapular upward rotation and winging adaptations; increased activity levels of MT, LT, and LS; decreased activity levels of SAlow; and increased scapular muscle ratios.

Eccentric exercise ≠ eccentric contraction

Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series compliance. Therefore, this study investigated the impact of changing the activation timing and level (i.e., preactivation) of the contraction on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were used to assess muscle fascicle kinematics and muscle activity levels, respectively. Although joint kinematics were similar among MTU-stretch-hold contractions (∼40° rotation amplitude), increasing preactivation increased fascicle shortening and stretch amplitudes (9.9-23.2 mm, P ≤ 0.015). This led to increasing positive and negative fascicle work with increasing preactivation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of preactivation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5-7.6%, P = 0.559) by preactivation, but rFE was strongly correlated with peak fascicle force during stretch (rrm = 0.62, P = 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series compliance to better understand the mechanical drivers of adaptation to exercise.NEW & NOTEWORTHY Apparent eccentric exercises do not result in isolated eccentric contractions, but shortening-stretch contractions at the fascicle level. The amount of fascicle shortening and stretch depends on the preactivation during the exercise and cannot be estimated from the muscle-tendon unit (MTU) or joint kinematics. As different fascicle mechanics might trigger different adaptations to eccentric exercise, muscle-tendon unit series compliance and muscle preactivation need to be considered when eccentric exercise protocols are designed.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

Clinical trial registration

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

The effect of flywheel complex training with eccentric-overload on muscular adaptation in elite female volleyball players

This study aimed to compare the effects of 8 weeks (24 sessions) between flywheel complex training with eccentric overload and traditional complex training of well-trained volleyball players on muscle adaptation, including hypertrophy, strength, and power variables. Fourteen athletes were recruited and randomly divided into the flywheel complex training with an eccentric-overload group (FCTEO, n = 7) and the control group (the traditional complex training group, TCT, n = 7). Participants performed half-squats using a flywheel device or Smith machine and drop jumps, with three sets of eight repetitions and three sets of 12 repetitions, respectively. The variables assessed included the muscle thickness at the proximal, mid, and distal sections of the quadriceps femoris, maximal half-squats strength (1RM-SS), squat jump (SJ), countermovement jump (CMJ), and three-step approach jump (AJ). In addition, a two-way repeated ANOVA analysis was used to find differences between the two groups and between the two testing times (pre-test vs. post-test). The indicators of the FCTEO group showed a significantly better improvement (p < 0.05) in CMJ (height: ES = 0.648, peak power: ES = 0.750), AJ (height: ES = 0.537, peak power: ES = 0.441), 1RM-SS (ES = 0.671) compared to the TCT group and the muscle thicknes at the mid of the quadriceps femoris (ES = 0.504) after FCTEO training. Since volleyball requires lower limb strength and explosive effort during repeated jumps and spiking, these results suggest that FCTEO affects muscular adaptation in a way that improves performance in well-trained female volleyball players.

Progressive Irreversible Proprioceptive Piezo2 Channelopathy-Induced Lost Forced Peripheral Oscillatory Synchronization to the Hippocampal Oscillator May Explain the Onset of Amyotrophic Lateral Sclerosis Pathomechanism

Amyotrophic lateral sclerosis (ALS) is a mysterious lethal multisystem neurodegenerative disease that gradually leads to the progressive loss of motor neurons. A recent non-contact dying-back injury mechanism theory for ALS proposed that the primary damage is an acquired irreversible intrafusal proprioceptive terminal Piezo2 channelopathy with underlying genetic and environmental risk factors. Underpinning this is the theory that excessively prolonged proprioceptive mechanotransduction under allostasis may induce dysfunctionality in mitochondria, leading to Piezo2 channelopathy. This microinjury is suggested to provide one gateway from physiology to pathophysiology. The chronic, but not irreversible, form of this Piezo2 channelopathy is implicated in many diseases with unknown etiology. Dry eye disease is one of them where replenishing synthetic proteoglycans promote nerve regeneration. Syndecans, especially syndecan-3, are proposed as the first critical link in this hierarchical ordered depletory pathomechanism as proton-collecting/distributing antennas; hence, they may play a role in ALS pathomechanism onset. Even more importantly, the shedding or charge-altering variants of Syndecan-3 may contribute to the Piezo2 channelopathy-induced disruption of the Piezo2-initiated proton-based ultrafast long-range signaling through VGLUT1 and VGLUT2. Thus, these alterations may not only cause disruption to ultrafast signaling to the hippocampus in conscious proprioception, but could disrupt the ultrafast proprioceptive signaling feedback to the motoneurons. Correspondingly, an inert Piezo2-initiated proton-based ultrafast signaled proprioceptive skeletal system is coming to light that is suggested to be progressively lost in ALS. In addition, the lost functional link of the MyoD family of inhibitor proteins, as auxiliary subunits of Piezo2, may not only contribute to the theorized acquired Piezo2 channelopathy, but may explain how these microinjured ion channels evolve to be principal transcription activators.

Impact of warm-up methods on strength-speed for sprinters in athletics: a mini review

In athletics, achieving peak performance during competitions is crucial. Warm-up strategies play a crucial role in optimizing the strength-speed performance of sprinters in athletics, especially tailored to the physiological demands of speed events. The need to balance flexibility, prevent injuries, and enhance power output makes the selection of an effective warm-up protocol essential. This narrative review examines different warm-up methods used by athletes and their effects on strength-speed in sprinters in athletics. The main findings indicate that Foam Rolling (FR), Isometric Exercises and Pre-Competitive Massages have no significant effects on sprint performance. Static stretching and prolonged Pre-Competitive Massages have negative impacts on strength and power. The Vibration Platform enhances step length, step rate and running velocity, jump height and total number of jumps performed in a 30-s period in non-experienced sprinters. Eccentric Exercise increases vertical force, Post-Activation Potentiation (PAP) demonstrates a reduction in 100-meter time and short-term improvement in vertical and horizontal jumps. Blood Flow Restriction (BFR) significantly improving jump height and flight time. Various warm-up methods have been identified, some focusing on flexibility, others potentially detrimental, and some enhancing strength and power. Implementing effective warm-ups, particularly those promoting strength and power, poses a challenge for coaches seeking reliable alternatives to boost performance.

Involvement of the Transient Receptor Channels in Preclinical Models of Musculoskeletal Pain

BACKGROUND

Musculoskeletal pain is a condition that affects bones, muscles, and tendons and is present in various diseases and/or clinical conditions. This type of pain represents a growing problem with enormous socioeconomic impacts, highlighting the importance of developing treatments tailored to the patient's needs. TRP is a large family of non-selective cation channels involved in pain perception. Vanilloid (TRPV1 and TRPV4), ankyrin (TRPA1), and melastatin (TRPM8) are involved in physiological functions, including nociception, mediation of neuropeptide release, heat/cold sensing, and mechanical sensation.

OBJECTIVE

In this context, we provide an updated view of the most studied preclinical models of muscle hyperalgesia and the role of transient receptor potential (TRP) in these models.

METHODS

This review describes preclinical models of muscle hyperalgesia induced by intramuscular administration of algogenic substances and/or induction of muscle damage by physical exercise in the masseter, gastrocnemius, and tibial muscles.

RESULTS

The participation of TRPV1, TRPA1, and TRPV4 in different models of musculoskeletal pain was evaluated using pharmacological and genetic tools. All the studies detected the antinociceptive effect of respective antagonists or reduced nociception in knockout mice.

CONCLUSION

Hence, TRPV1, TRPV4, and TRPA1 blockers could potentially be utilized in the future for inducing analgesia in muscle hypersensitivity pathologies.

Re‑examining the mechanism of eccentric exercise‑induced skeletal muscle damage from the role of the third filament, titin (Review)

Intense and unaccustomed eccentric exercise has been extensively studied for its ability to induce muscle damage. However, the underlying mechanism of this phenomenon still requires further clarification. This knowledge gap arises from the need for explanation of the eccentric contraction through the sliding filament theory. The two-filament sarcomere model, which is consisted of thin and thick filaments, forms the basis of the sliding filament theory. The mechanisms of concentric and isometric contractions at the cellular and molecular levels are effectively described by this model. However, when relying solely on the cross-bridge swing, the sliding filament theory fails to account for specific observations, such as the stability of the descending limb of the force-length relationship curve. Recent evidence indicated that titin and the extracellular matrix (ECM) may play a protective role by interacting with the thick and thin filaments. During an eccentric contraction, titin serves as a third filament in the sarcomere, which helps regulate changes in passive force. The two-filament sarcomere model has limitations in explaining eccentric contraction, thus this compensates for those shortcomings. The present review explored the potential of replacing the two-filament sarcomere model with a three-filament sarcomere model, incorporating thin filaments, thick filaments and titin. This revised model offers a more comprehensive explanation of eccentric contraction phenomena. Furthermore, the sliding filament theory was investigated in the context of the three-filament sarcomere model. The double-layer protection mechanism, which involves increased titin stiffness and the ECM during eccentric contraction was explored. This mechanism may enhance lateral force transmission between muscle fibers and the ECM, resulting in sarcolemma and ECM shear deformation. These findings provided insight into the mechanism of eccentric exercise-induced skeletal muscle damage. Considering the three-filament sarcomere model and the double-layer protection mechanism, the present review offered a more logical and comprehensive understanding of the mechanism behind eccentric exercise-induced muscle damage.

Association between Gray-Scale Ultrasound Imaging and Serological Creatine Kinase for Quantifying Exercise-Induced Muscle Damage: An Observational Study

Limited evidence has verified if ultrasound imaging (US) can detect post-exercise muscle damage based on size, shape, and brightness metrics. This study aimed to analyze the correlation between creatine kinase (CK) concentration and (as a biomarker of muscle damage) changes in US gray-scale metrics after an exercise-induced muscle damage protocol. An observational study was conducted at a private university lab located in Madrid. Twenty-five untrained and asymptomatic volunteers were enrolled in this study. Baseline demographic data and body composition metrics were collected. In addition, the rectus femoris US data and CK concentration were assessed at baseline and after inducing muscle damage (24 and 48 h later). After calculating time differences for all the outcomes, the correlation between the changes observed with US and biomarkers was assessed. Significant CK concentration increases were found 24 h (p = 0.003) and 48 h (p < 0.001) after exercise. However, no significant changes in muscle size, shape, or brightness were found in any location (p > 0.05 for all). In addition, no significant associations were found between CK changes and US changes (p > 0.05 for all). Gray-scale US is not a sensitive tool for detecting muscle damage, as a protocol of exercise-induced muscle damage confirmed with CK produced no significant gray-scale US changes after 24 or 48 h. In addition, US and CK changes after 24 and 48 h were not associated with each other.

Electrically stimulated eccentric contraction training enhances muscle mass, function, and size following volumetric muscle loss

Volumetric muscle loss (VML) overwhelms muscle's innate capacity for repair and can lead to permanent disability. The standard of care for VML injuries includes physical therapy, which can improve muscle function. The objective of this study was to develop and evaluate a rehabilitative therapy using electrically stimulated eccentric contraction training (EST) and determine the structural, biomolecular, and functional response of the VML-injured muscle. This study implemented EST using three different frequencies (50, 100, and 150 Hz) in VML-injured rats starting at 2 weeks postinjury. Four weeks of EST at 150 Hz showed a progressive increase in eccentric torque with an improvement in muscle mass (~39%), myofiber cross-sectional area, and peak isometric torque (~37.5%) relative to the untrained VML-injured sham group. EST at 150 Hz group also increased the number of large type 2B fibers (>5000 µm2 ). Elevated gene expression of markers associated with angiogenesis, myogenesis, neurogenesis, and an anti-inflammatory response was also observed. These results suggest that VML-injured muscles can respond and adapt to eccentric loading. The results of this study may aid in developing physical therapy regimens for traumatized muscles.

Eccentric Contractions of the Diaphragm During Mechanical Ventilation

Diaphragm dysfunction is a highly prevalent phenomenon in patients receiving mechanical ventilation, mainly due to ventilatory over-assistance and the development of diaphragm disuse atrophy. Promoting diaphragm activation whenever possible and facilitating an adequate interaction between the patient and the ventilator is encouraged at the bedside to avoid myotrauma and further lung injury. Eccentric contractions of the diaphragm are defined as muscle activation while muscle fibers are lengthening within the exhalation phase. There is recent evidence that suggests that eccentric activation of the diaphragm is very frequent and may occur during post-inspiratory activity or under different types of patient-ventilator asynchronies, which include ineffective efforts, premature cycling, and reverse triggering. The consequences of this eccentric contraction of the diaphragm may have opposite effects, depending on the level of breathing effort. For instance, during high or excessive effort, eccentric contractions can result in diaphragm dysfunction and injured muscle fibers. Conversely, when eccentric contractions of the diaphragm occur along with low breathing effort, a preserved diaphragm function, better oxygenation, and more aerated lung tissue are observed. Despite this controversial evidence, evaluating the level of breathing effort at the bedside seems crucial and is highly recommended to optimize ventilatory therapy. The impact of eccentric contractions of the diaphragm on the patient's outcome remains to be elucidated.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

Clinical trial registration

ClinicalTrials.gov, identifier ID: NCT05220371.

Reverse triggering during mechanical ventilation: Diagnosis and clinical implications

This review addresses the phenomenon of "reverse triggering", an asynchrony that occurs in deeply sedated patients or patients in transition from deep to light sedation. Reverse triggering has been reported to occur in 30-90% of all ventilated patients. The underlying pathophysiological mechanisms remain unclear, but "entrainment" is proposed as one of them. Detecting this asynchrony is crucial, and methods such as visual inspection, esophageal pressure, diaphragmatic ultrasound and automated methods have been used. Reverse triggering may have effects on lung and diaphragm function, probably mediated by the level of breathing effort and eccentric activation of the diaphragm. The optimal management of reverse triggering has not been established, but may include the adjustment of ventilatory parameters as well as of sedation level, and in extreme cases, neuromuscular block. It is important to understand the significance of this condition and its detection, but also to conduct dedicated research to improve its clinical management and potential effects in critically ill patients.

Probing muscle recovery following downhill running using precise mapping of MRI T2 relaxation times

PURPOSE

Postexercise recovery rate is a vital component of designing personalized training protocols and rehabilitation plans. Tracking exercise-induced muscle damage and recovery requires sensitive tools that can probe the muscles' state and composition noninvasively.

METHODS

Twenty-four physically active males completed a running protocol consisting of a 60-min downhill run on a treadmill at -10% incline and 65% of maximal heart rate. Quantitative mapping of MRI T2 was performed using the echo-modulation-curve algorithm before exercise, and at two time points: 1 h and 48 h after exercise.

RESULTS

T2 values increased by 2%-4% following exercise in the primary mover muscles and exhibited further elevation of 1% after 48 h. For the antagonist muscles, T2 values increased only at the 48-h time point (2%-3%). Statistically significant decrease in the SD of T2 values was found following exercise for all tested muscles after 1 h (16%-21%), indicating a short-term decrease in the heterogeneity of the muscle tissue.

CONCLUSION

MRI T2 relaxation time constitutes a useful quantitative marker for microstructural muscle damage, enabling region-specific identification for short-term and long-term systemic processes, and sensitive assessment of muscle recovery following exercise-induced muscle damage. The variability in T2 changes across different muscle groups can be attributed to their different role during downhill running, with immediate T2 elevation occurring in primary movers, followed by delayed elevation in both primary and antagonist muscle groups, presumably due to secondary damage caused by systemic processes.