Indirect evidence of human skeletal muscle damage and collagen breakdown after eccentric muscle actions

Identification of EIMD Level Differences Between Long- and Short Head of Biceps Brachii Using Echo Intensity and GLCM Texture Features

Purpose: This study aimed to compare the time-course changes of exercise-induced muscle damage (EIMD) levels in the long head of biceps brachii (LHB) and short head of the biceps brachii (SHB) using echo intensity (EI) and to determine the efficiency of the gray level co-occurrence matrix (GLCM) texture parameters. Methods: The participants performed 30 maximal eccentric contractions of the elbow flexor. Along with muscle damage indicators, including circumference, range of motion, muscle soreness, and maximal voluntary isometric contraction (MVIC), the EI and GLCM texture features of the LHB and SHB was also assessed using B-mode ultrasonography. All measurements were assessed pre- and immediately post-exercise and after 24, 48, 72, and 96 h. Results: The muscle damage indicators indicated significant changes after the eccentric contractions (p < 0.01 for circumference, range of motion, muscle soreness, and MVIC). The EI of LHB significantly increased following the contractions (p < 0.01), but that of SHB did not (p > 0.05). In contrast, for the GLCM texture parameters, there were significant changes in the SHB (p < 0.01 for homogeneity, energy, and entropy). Conclusion: Thus, this study demonstrated that EIMD severity is different between LHB and SHB even within the same muscle. In the GLCM features, the time course of SHB after eccentric contraction revealed different patterns compared with those of LHB. Therefore, even if there are no changes in EI within a target muscle following muscle contractions, new information on muscle quality can be obtained through GLCM analysis.

The Response of the Amputee Athlete Heart to Chronic Core Exercise: A Study on Hematological and Biochemical Parameters, and N-Terminal Pro Brain Natriuretic Peptide

Background and Objectives: mortality and morbidity due to cardiovascular causes are frequently experienced in amputees. Research on the effects of chronic exercise on biomarkers and cardiac damage indicators in these individuals is limited. The aim of this study was to investigate the effects of a core training program on brain natriuretic-related peptide, as well as hematological and biochemical parameters in amputee soccer players. Materials and Methods: The participants were randomly allocated to the following two groups: a core exercise group (CEG) and a control group (CG). While the CG continued routine soccer training, the CEG group was included in a core exercise program different from this group. During the study, routine hemogram parameters of the participants, various biochemical markers, and the concentration of brain natriuretic-related peptide (NT-pro-BNP) were analyzed. Results: after the training period, notable improvements in various hematological parameters were observed in both groups. In the CEG, there were significant enhancements in red blood cell count (RBC), hematocrit (HCT), mean corpuscular hemoglobin concentration (MCHC), and mean corpuscular hemoglobin (MCH) values. Similarly, the CG also showed substantial improvements in RBC, HCT, mean corpuscular volume (MCV), MCHC, MCH, red cell distribution width-standard deviation (RDW-SD), platelet-to-lymphocyte ratio (PLCR), mean platelet volume (MPV), and platelet distribution width (PDW). Moreover, in the CEG, serum triglycerides (TG) and maximal oxygen uptake (MaxVO2) exhibited significant increases. Conversely, TG levels decreased in the CG, while high-density lipoprotein (HDL), low-density lipoprotein (LDL), and MaxVO2 levels demonstrated substantial elevations. Notably, the N-terminal pro-brain natriuretic peptide (BNP) levels did not undergo significant changes in either the CEG or the CG following the core exercise program (p > 0.05). However, in the CEG, a meaningful positive correlation was observed between NT-pro-BNP and creatine kinase (CK) levels before and after the core exercise program. Conclusions: the findings emphasized the potential benefits of core training in enhancing specific physiological aspects, such as erythrocyte-related parameters and lipid metabolism, as well as aerobic capacity. Furthermore, the observed correlation between NT-pro-BNP and CK levels in the CEG provides intriguing insights into the unique physiological adaptations of amputee athletes.

Plasma α-Actin as an Early Marker of Muscle Damage After Repeated Bouts of Eccentric Cycling

Purpose: This study aimed to examine the changes in skeletal muscle (SM) α-actin, myoglobin (Mb) and hydroxyproline (HP) in plasma and other indirect markers of muscle damage after repeated bouts of eccentric cycling. Methods: Ten healthy men (23.3 ± 2.8 years) performed two 30-min eccentric cycling bouts at 100% of maximal concentric power output (230.7 ± 36.9 W) separated by 2 weeks (ECC1 and ECC2). Maximal voluntary isometric contraction (MVIC) peak force of the knee extensor muscles, muscle soreness (SOR), pain pressure threshold (PPT) and plasma levels of SM α-actin, Mb, and HP were measured before, 0.5, 3, 24-168 h after each cycling bout. Results: MVIC peak force decreased on average 10.7 ± 13.1% more after ECC1 than ECC2. SOR was 80% greater and PPT was 12-14% lower after ECC1 than ECC2. Plasma SM α-actin levels increased at 0.5, 3, and 24-72 h after ECC1 (26.1-47.9%), and SM α-actin levels at 24 h after ECC1 were associated with muscle strength loss (r = -0.56, P = .04) and SOR (r = 0.88, P = .001). Mb levels increased at 0.5, 3, and 24 h after ECC1 (200-502%). However, Mb levels at 24 h after ECC1were not associated with muscle strength loss and SOR. HP levels remained unchanged after ECC1. ECC2 did not increase SM α-actin, Mb and HP levels. Conclusion: Our results indicate that α-actin could be used as a potential marker for the early identification of SM damage due to its early appearance in plasma and its association with other indirect markers of muscle damage.

Effects of High-Intensity, Eccentric-Only Muscle Actions on Serum Biomarkers of Collagen Degradation and Synthesis

ABSTRACT

Neltner, TJ, Sahoo, PK, Smith, RW, Anders, JPV, Arnett, JE, Ortega, DG, Schmidt, RJ, Johnson, GO, Natarajan, SK, and Housh, TJ. Effects of high-intensity, eccentric-only muscle actions on serum biomarkers of collagen degradation and synthesis. J Strength Cond Res 37(9): 1729-1737, 2023-The purpose of this study was to examine the effects of high-intensity, eccentric-only muscle actions of the leg extensors on (a) serum biomarkers of collagen degradation (hydroxyproline [HYP] and C-terminal telopeptide of type I collagen [C1M]) and synthesis (pro-c1α1) and (b) the time course of changes in maximal voluntary isometric contraction (MVIC) and ratings of muscle soreness after the eccentric-only exercise bout. Twenty-five recreationally active men (mean ± SD: age = 21.2 ± 2.0 years) completed 5 sets of 10 bilateral, eccentric-only dynamic constant external resistance muscle actions of the leg extensors at a load of 110% of their concentric leg extension 1 repetition maximum. Analysis of variances (p < 0.05) and a priori planned pairwise comparisons using Bonferroni corrected (p < 0.0167) paired t tests were used to examine mean changes in blood biomarkers from baseline to 48 hours postexercise as well as in MVIC and soreness ratings immediately, 24 hours, and 48 hours postexercise. There were increases in HYP (3.41 ± 2.37 to 12.37 ± 8.11 μg·ml-1; p < 0.001) and C1M (2.50 ± 1.05 to 5.64 ± 4.89 μg·L-1; p = 0.003) from preexercise to 48 hours postexercise, but no change in pro-c1α1. Maximal voluntary isometric contraction declined immediately after the exercise bout (450.44 ± 72.80 to 424.48 ± 66.67 N·m; p = 0.002) but recovered 24 hours later, whereas soreness was elevated immediately (6.56 ± 1.58; p < 0.001), 24 hours (3.52 ± 1.53; p < 0.001), and 48 hours (2.60 ± 1.32; p = 0.001) postexercise. The eccentric-only exercise bout induced increases in collagen degradation but had no effect on collagen synthesis. These findings provide information for clinicians to consider when prescribing exercise after an acute injury or surgery.

Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging

Skeletal muscle extracellular matrix (ECM) is critical for muscle force production and the regulation of important physiological processes during growth, regeneration, and remodelling. ECM remodelling is a tightly orchestrated process, sensitive to multi-directional tensile and compressive stresses and damaging stimuli, and its assessment can convey important information on rehabilitation effectiveness, injury, and disease. Despite its profound importance, ECM biomarkers are underused in studies examining the effects of exercise, disuse, or aging on muscle function, growth, and structure. This review examines patterns of short- and long-term changes in the synthesis and concentrations of ECM markers in biofluids and tissues, which may be useful for describing the time course of ECM remodelling following physical activity and disuse. Forces imposed on the ECM during physical activity critically affect cell signalling while disuse causes non-optimal adaptations, including connective tissue proliferation. The goal of this review is to inform researchers, and rehabilitation, medical, and exercise practitioners better about the role of ECM biomarkers in research and clinical environments to accelerate the development of targeted physical activity treatments, improve ECM status assessment, and enhance function in aging, injury, and disease.

The Relationship Between Acute Exercise-Induced Changes in Extramuscular Connective Tissue Thickness and Delayed Onset Muscle Soreness in Healthy Participants: A Randomized Controlled Crossover Trial

Background

The extramuscular connective tissue (ECT) has been shown to play a significant role in mechanical force transmission between musculoskeletal structures. Due to this and owing to its tight connection with the underlying muscle, the ECT may be vulnerable to excessive loading. The present study aimed to investigate the effect of eccentric elbow flexor exercise on the morphology of the biceps brachii ECT. In view of the high nociceptive capacity of the ECT, an additional objective was to elucidate the potential relationship between ECT damage and the occurrence of delayed onset muscle soreness (DOMS).

Methods

Eleven healthy participants (♂ = 7; 24 ± 2 years) performed fatiguing dumbbell elbow flexor eccentric exercise (EE) for one arm and concentric exercise (CE) for the other arm in random order and with random arm allocation. Before, immediately after and 24–96 h post-exercise, maximal voluntary isometric contraction torque of the elbow flexors (dynamometer), pressure pain (algometer), palpation pain (100 mm visual analog scale), biceps brachii ECT thickness and ECT/muscle mobility during passive movement (both high-resolution ultrasound) were examined.

Results

Palpation pain, suggestive of DOMS, was greater after EE than CE, and maximal voluntary isometric contraction torque decreased greater after EE than CE (p < .05). Relative to CE, EE increased ECT thickness at 48 (+ 17%), 72 (+ 14%) and 96 (+ 15%) hours post-exercise (p < .05). At 96 h post-EE, the increase in ECT thickness correlated with palpation pain (r = .68; p < .05). ECT mobility was not different between conditions, but compared to CE, muscle displacement increased at 24 (+ 31%), 72 (+ 31%) and 96 (+ 41%) hours post-EE (p < .05).

Conclusion

Collectively, these results suggest an involvement of the ECT changes in delayed onset muscle soreness.

Exercise-Induced Muscle Damage and Protein Intake: A Bibliometric and Visual Analysis

Numerous studies have covered exercise-induced muscle damage (EIMD) topics, ranging from nutritional strategies to recovery methods, but few attempts have adequately explored and analyzed large volumes of scientific output. The purpose of this study was to assess the scientific output and research activity regarding EIMD and protein intake by conducting a bibliometric and visual analysis. Relevant publications from 1975-2022 were retrieved from the Web of Science Core Collection database. Quantitative and qualitative variables were collected, including the number of publications and citations, H-indexes, journals of citation reports, co-authorship, co-citation, and the co-occurrence of keywords. There were 351 total publications, with the number of annual publications steadily increasing. The United States has the highest total number of publications (26.21% of total publications, centrality 0.44). Institutional cooperation is mostly geographically limited, with few transnational cooperation links. EIMD and protein intake research is concentrated in high-quality journals in the disciplines of Sport Science, Physiology, Nutrition, and Biochemistry & Molecular Biology. The top ten journals in the number of publications are mostly high-quality printed journals, and the top ten journals in centrality have an average impact factor of 13.845. The findings of the co-citation clusters and major keyword co-occurrence reveal that the most discussed research topics are "exercise mode", "nutritional strategies", "beneficial outcomes", and "proposed mechanisms". Finally, we identified the following research frontiers and research directions: developing a comprehensive understanding of new exercise or training models, nutritional strategies, and recovery techniques to alleviate EIMD symptoms and accelerate recovery; applying the concept of hormesis in EIMD to induce muscle hypertrophy; and investigating the underlying mechanisms of muscle fiber and membrane damage.

A Short-Term Eccentric HIIT Induced Greater Reduction in Cardio-Metabolic Risk Markers in Comparison With Concentric HIIT in Sedentary Overweight Men

Background: Steady-state eccentric exercise training improves cardiometabolic risk (CMR) despite lesser cardiovascular demands compared with load-matched concentric training. Whether a high-intensity interval eccentric training is also effective reducing CMR is unknown. Aim: To compare the effects of a short-term high-intensity interval eccentric training (ECC-HIIT) with high-intensity interval concentric training (CONC-HIIT) on CMR in sedentary overweight men. Methods: Twenty men (age: 27.9 ± 5.3y, body massindex: 29.1 ± 3.1 kg·m-2) were randomly assigned to ECC-HIIT (n = 10) or CONC-HIIT (n = 10) delivered as six sessions, including 4 x 5:2 min work-to-rest ratio, at 80% peak concentric power output. Heart rate (HR), rate of perceived exertion (RPE) and muscle soreness weremonitored during training sessions. Training effects on lipid profile, insulin sensitivity (HOMA-IR), body composition, thigh circumference, isometric knee extensors maximal strength, resting systolic and diastolic blood pressure (SBP and DBP) were determined. Results: Average training HR and RPE were -29%and -50%lower in ECC-HIIT in comparison with CONC-HIIT. Muscle soreness was initially greater after ECC-HIIT compared with CONC-HIIT. Significant changes in total and low-density lipoprotein cholesterol (-7.0 ± 8.7%; p = .02 and -6.3 ± 14.4%; p = .03), SBP (-9.8 ± 7.8%; p = .002), and maximal thigh circumference (+2.5 ± 3.1%; p = .02) were observed following ECC-HIIT. No changes in any CMR marker were observed after CONC-HIIT. Moderate-to-large training effect sizes were obtained in thigh circumference, SBP, total cholesterol and low-density lipoprotein cholesterol in response to ECC-HIIT. Conclusion: A two-week ECC-HIIT was well-tolerated and induced rapid onset improvements in cholesterol and blood pressure compared to conventional CONC-HIIT in sedentary overweight men.

Expression of tissue remodelling, inflammation- and angiogenesis-related factors after eccentric exercise in humans

Eccentric exercise has been extensively used as a model to study the contraction-induced muscle damage and its consequent processes. This study aimed at examining molecular responses associated with tissue remodelling, inflammation and angiogenesis in skeletal muscle during the recovery period after eccentric exercise in humans. Ten healthy men performed 50 maximal eccentric muscle actions with the knee extensors and muscle biopsies were collected from the vastus lateralis before and 6 h, 48 h and 120 h post eccentric exercise. Real Time-PCR was utilized to investigate alterations in gene expression of various tissue remodelling-, inflammation- and angiogenesis-related factors: uPA, uPA-R, TGF-β1, MMP-9, TNF-α, IL-6, IL-8, VEGF, VEGFR-2, HIF-1a, Ang-1, Ang-2 and Tie-2. The uPA/uPA-R system exhibited a similar time-expression pattern increasing 6 h post exercise (p < 0.05), while the other tissue remodelling factors TGF-β1 and MMP-9 did not change significantly over time. Transcriptional responses of inflammatory factors TNF-α and IL-8 increased significantly and peaked 6 h post eccentric exercise (p < 0.05), while IL-6 exhibited a similar, though not statistically significant, expression profile (p > 0.05). Similarly, the expression of angiopoietin receptor Tie-2 showed an early increase only at 6 h after the completion of exercise (p < 0.05), while the other angiogenic factors failed to reach statistical significance due a high interindividual variability in the gene expression responses. The early transcriptional upregulation of tissue remodelling, inflammation- and angiogenesis-related factors post eccentric exercise may indicate the acute intramuscular activation of these processes functionally related to muscle damage-induced adaptation.

Changes in plasma hydroxyproline and plasma cell-free DNA concentrations after higher- versus lower-intensity eccentric cycling

PURPOSE

We examined changes in plasma creatine kinase (CK) activity, hydroxyproline and cell-free DNA (cfDNA) concentrations in relation to changes in maximum voluntary isometric contraction (MVIC) torque and delayed-onset muscle soreness (DOMS) following a session of volume-matched higher- (HI) versus lower-intensity (LI) eccentric cycling exercise.

METHODS

Healthy young men performed either 5 × 1-min HI at 20% of peak power output (n = 11) or 5 × 4-min LI eccentric cycling at 5% of peak power output (n = 9). Changes in knee extensor MVIC torque, DOMS, plasma CK activity, and hydroxyproline and cfDNA concentrations before, immediately after, and 24-72 h post-exercise were compared between groups.

RESULTS

Plasma CK activity increased post-exercise (141 ± 73.5%) and MVIC torque decreased from immediately (13.3 ± 7.8%) to 48 h (6.7 ± 13.5%) post-exercise (P < 0.05), without significant differences between groups. DOMS was greater after HI (peak: 4.5 ± 3.0 on a 10-point scale) than LI (1.2 ± 1.0). Hydroxyproline concentration increased 40-53% at 24-72 h after both LI and HI (P < 0.05). cfDNA concentration increased immediately after HI only (2.3 ± 0.9-fold, P < 0.001), with a significant difference between groups (P = 0.002). Lack of detectable methylated HOXD4 indicated that the cfDNA was not derived from skeletal muscle. No significant correlations were evident between the magnitude of change in the measures, but the cfDNA increase immediately post-exercise was correlated with the maximal change in heart rate during exercise (r = 0.513, P = 0.025).

CONCLUSION

Changes in plasma hydroxyproline and cfDNA concentrations were not associated with muscle fiber damage, but the increased hydroxyproline in both groups suggests increased collagen turnover. cfDNA may be a useful metabolic-intensity exercise marker.

Remodeling the Skeletal Muscle Extracellular Matrix in Older Age-Effects of Acute Exercise Stimuli on Gene Expression

With advancing age, the skeletal muscle extracellular matrix (ECM) undergoes fibrotic changes that may lead to increased muscle stiffness, injury susceptibility and strength loss. This study tested the potential of different exercises to counter these changes by stimulating the activity of genes associated with ECM remodeling. Twenty-six healthy men (66.9 ± 3.9 years) were stratified to two of four groups, performing unilateral (i) conventional resistance exercise, (ii) conventional resistance exercise followed by self-myofascial release (CEBR), (iii) eccentric-only exercise (ECC) or (iv) plyometric jumps (PLY). The non-trained leg served as control. Six hours post-exercise, vastus lateralis muscle biopsy samples were analyzed for the expression of genes associated with ECM collagen synthesis (COL1A1), matrix metallopeptidases (collagen degradation; MMPs) and peptidase inhibitors (TIMP1). Significant between-group differences were found for MMP3, MMP15 and TIMP1, with the greatest responses in MMP3 and TIMP1 seen in CEBR and in MMP15 in ECC. MMP9 (3.24–3.81-fold change) and COL1A1 (1.47–2.40-fold change) were increased in CEBR and PLY, although between-group differences were non-significant. The expression of ECM-related genes is exercise-specific, with CEBR and PLY triggering either earlier or stronger remodeling than other stimuli. Training studies will test whether execution of such exercises may help counter age-associated muscle fibrosis.

Skeletal Muscle Extracellular Matrix - What Do We Know About Its Composition, Regulation, and Physiological Roles? A Narrative Review

Skeletal muscle represents the largest body-composition component in humans. In addition to its primary function in the maintenance of upright posture and the production of movement, it also plays important roles in many other physiological processes, including thermogenesis, metabolism and the secretion of peptides for communication with other tissues. Research attempting to unveil these processes has traditionally focused on muscle fibers, i.e., the contractile muscle cells. However, it is a frequently overlooked fact that muscle fibers reside in a three-dimensional scaffolding that consists of various collagens, glycoproteins, proteoglycans, and elastin, and is commonly referred to as extracellular matrix (ECM). While initially believed to be relatively inert, current research reveals the involvement of ECM cells in numerous important physiological processes. In interaction with other cells, such as fibroblasts or cells of the immune system, the ECM regulates muscle development, growth and repair and is essential for effective muscle contraction and force transmission. Since muscle ECM is highly malleable, its texture and, consequently, physiological roles may be affected by physical training and disuse, aging or various diseases, such as diabetes. With the aim to stimulate increased efforts to study this still poorly understood tissue, this narrative review summarizes the current body of knowledge on (i) the composition and structure of the ECM, (ii) molecular pathways involved in ECM remodeling, (iii) the physiological roles of muscle ECM, (iv) dysregulations of ECM with aging and disease as well as (v) the adaptations of muscle ECM to training and disuse.

The effects of Shilajit supplementation on fatigue-induced decreases in muscular strength and serum hydroxyproline levels

Background

Shilajit is a safe, fluvic mineral complex exudate that is common to Ayurvedic medicine and is composed of fulvic acids, dibenzo-α-pyrones, proteins, and minerals. The purpose of this study was to examine the effects of 8 weeks of Shilajit supplementation at 250 mg·d^− 1 (low dose) and 500 mg·d^− 1 (high dose) versus placebo on maximal voluntary isometric contraction (MVIC) strength, concentric peak torque, fatigue-induced percent decline in strength, and serum hydroxyproline (HYP).

Methods

Sixty-three recreationally-active men (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{X} $$\end{document}X¯ ± SD: 21.2 ± 2.4 yr.; 179.8 ± 6.3 cm; 83.1 ± 12.7 kg) volunteered to participate in this study. The subjects were randomly assigned to the high dose, low dose, or placebo group (each group: n = 21). During pre-supplementation testing, the subjects performed 2 pretest MVICs, 2 sets of 50 maximal, bilateral, concentric isokinetic leg extensions at 180°·s^− 1 separated by 2-min of rest, and 2 posttest MVICs. Following 8 weeks of supplementation, the subjects repeated the pre-supplementation testing procedures. In addition, the groups were dichotomized at the 50th percentile based on pre-supplementation MVIC and baseline HYP. Mixed model ANOVAs and ANCOVAs were used to statistically analyze the dependent variables for the total groups (n = 21 per group) as well as dichotomized groups.

Results

For the upper 50th percentile group, the post-supplementation adjusted mean percent decline in MVIC was significantly less for the high dose group (8.9 ± 2.3%) than the low dose (17.0 ± 2.4%; p = 0.022) and placebo (16.0 ± 2.4%; p = 0.044) groups. There was no significant (p = 0.774) difference, however, between the low dose and placebo groups. In addition, for the upper 50th percentile group, the adjusted mean post-supplementation baseline HYP for the high dose group (1.5 ± 0.3 μg·mL^− 1) was significantly less than both the low dose (2.4 ± 0.3 μg·mL^− 1; p = 0.034) and placebo (2.4 ± 0.3 μg·mL^− 1, p = 0.024) groups.

Conclusions

The results of the present study demonstrated that 8 weeks of PrimaVie® Shilajit supplementation at 500 mg·d^− 1 promoted the retention of maximal muscular strength following the fatiguing protocol and decreased baseline HYP. Thus, PrimaVie® Shilajit supplementation at 500 mg·d^− 1 elicited favorable muscle and connective tissue adaptations.

Metabolic Profiling of Eccentric Exercise-Induced Muscle Damage in Human Urine

Skeletal muscle can be ultrastructurally damaged by eccentric exercise, and the damage causes metabolic disruption in muscle. This study aimed to determine changes in the metabolomic patterns in urine and metabolomic markers in muscle damage after eccentric exercise. Five men and 6 women aged 19~23 years performed 30 min of the bench step exercise at 70 steps per min at a determined step height of 110% of the lower leg length, and stepping frequency at 15 cycles per min. ¹H NMR spectral analysis was performed in urine collected from all participants before and after eccentric exercise-induced muscle damage conventionally determined using a visual analogue scale (VAS) and maximal voluntary contraction (MVC). Urinary metabolic profiles were built by multivariate analysis of principal component analysis (PCA) and orthogonal partial least square-discriminant analysis (OPLS-DA) using SIMCA-P. From the OPLS-DA, men and women were separated 2 hr after the eccentric exercise and the separated patterns were maintained or clarified until 96 hr after the eccentric exercise. Subsequently, urinary metabolic profiles showed distinct trajectory patterns between men and women. Finally, we found increased urinary metabolites (men: alanine, asparagine, citrate, creatine phosphate, ethanol, formate, glucose, glycine, histidine, and lactate; women: adenine) after the eccentric exercise. These results could contribute to understanding metabolic responses following eccentric exercise-induced muscle damage in humans.

Skeletal Muscle Cell Damage Indicators in Volleyball Players after the Competitive Phase of the Annual Training Cycle

The aim of the study was to evaluate the impact of the competitive phase on physiological and metabolic indices and selected markers of skeletal muscle damage in male volleyball players. The study group consisted of 24 young male volleyball players. During the study, participants underwent two series of measurements, before and after the competitive phase of the annual training cycle. In both study terms, players performed an incremental treadmill running test to determine their ventilatory threshold and maximal oxygen uptake. Venous and capillary blood samples were taken for biochemical analysis. There was no significant difference in the physical fitness level, values of biochemical variables and the level of antioxidant status in the surveyed athletes between the two study terms. Significant changes within skeletal muscle damage markers were observed between the beginning and the end of the competitive period: an increase in the concentration of cellular DNA damage products (8-hydroxy-2'-deoxyguanosine; p < 0.0001) and a decrease in muscle activity of creatine kinase (p<0.05). In spite of the increment in cell damage markers, the unaffected level of physiological and biochemical markers may indicate that the experienced cell destruction did not negatively affect the level of physical fitness. When designing the annual training plan, coaches and athletes need to take into consideration that temporary physiological states - oxidative stress and inflammation - may be required to attain training adaptation.

Association between Match Activity Variables, Measures of Fatigue and Neuromuscular Performance Capacity Following Elite Competitive Soccer Matches

The aim of the study was to assess the relationships between match activity variables, subsequent fatigue and neuromuscular performance capacity in elite soccer players. Subjects (n = 10) were professional soccer players participating in the English Championships. Match activity variables and markers of fatigue status were measured before and following two matches. Creatine kinase (CK) and muscle soreness were measured at baseline, immediately following, as well as 40 and 64 h post-match. Countermovement jump performance and perceived ratings of wellness were measured at baseline, then 40 and 64 h post-match. Relationships were shown between CK and the total number of accelerations and decelerations immediately (r = 0.63; large), 40 h (r = 0.45; moderate) and 64 h post-match (r = 0.35; moderate) (p < 0.05). Relationships between CK and total sprint distance (r = 0.39; moderate) and the number of sprints (r = 0.35; moderate) 40 h post-match (p < 0.05) were observed. Furthermore, relationships were shown between the perceived rating of wellness and number of accelerations 40 (r = 0.52; large) and 64 h (r = 0.40; moderate) post-match, sprint distance 40 h post-match (r = 0.40; moderate) and the total number of sprints 40 h post-match (r = 0.51; large) (p < 0.05). The quantification of match activity variables, particularly the total number of accelerations and decelerations and the number of sprints, provides insights into the fatigue status in elite soccer players 40 and 64 h post-match.

The effects of the intake of an isotonic sports drink before orienteering competitions on skeletal muscle damage

[Purpose] The purpose of this study was to investigate the effects of the intake of an isotonic sports drink (500 ml water, 32 gr carbonhydrate, 120 mg calcium, 248 mg chloride, 230 mg sodium) the level of the skeletal muscle damage of orienteering athletes. [Subjects and Methods] The study was carried out on 21 male elite orienteering athletes. The athletes were divided into two groups by randomized double-blind selection. The experimental group (n=11) was given the isotonic sports drink, while the placebo group (n=10) was given 500 ml pure water. Blood samples were taken pre-competition, post-competition, 2 hours post-competition and 24 hours post-competition. [Results] The pre-c troponin, myoglobin and creatinine kinase serum levels of the placebo group were significantly lower than the post-competition and 2 hours post-competition values. The 24 hours post-competition levels of the same analyses were also significantly lower than the post-c and 2 hours post-competition. The pre-competition troponin, myoglobin and creatinine kinase levels of the experimental group were found to be significantly lower than the post-competition, 2 hours post-competition 24 hours post-competition values. In conclusion, the present results suggest that the intake of supportive sports drinks before exercising significantly prevents the observed muscle damage. The study showed that serum myoglobin levels between the experimental and the placebo group is significantly different during the 2 hours post-competition period. [Conclusion] The level of serum creatinine kinase and myoglobin accurately shows the extent of the muscle damage. However, further studies on the effect of isotonic sports drink in different training programs on the cell membrane and the muscle damage are needed.

Polyamines, myosin heavy chains, and collagen specific amino acids after a repeated bout of eccentric exercise

We investigated alternatives to commonly used biomarkers of exercise-induced tissue damage. Over 5 days following two bouts of 100 drop-to-vertical jumps (inter-bout rest period of 3 weeks), myosin heavy chain 1, hydroxylysine (HYL), hydroxyproline (HYP), spermine (SPM) and spermine synthase (SMS) were measured in the serum of 10 participants. HYL significantly increased from 5.92 ± 1.49 ng/mL to 6.48 ± 1.47 ng/mL at 24 h. A similar trend was observed for bout 2, but without reaching significance. SPM significantly increased only after bout 1 from 0.96 ± 0.19 ng/mL at pretest to a peak level of 1.12 ± 0.26 ng/mL at 24 h, while B2 increments remained non-significant. Myosin heavy chain 1, HYP and SMS values remained below the detection limit of the applied enzyme-linked immunosorbent assay (ELISA) kit. Though HYL and SM increased after the intervention, both markers showed a large standard deviation (SD) combined with small increments. Therefore, none of the investigated biomarkers provides a meaningful alternative to commonly used damage markers.

Genetic variation and exercise-induced muscle damage: implications for athletic performance, injury and ageing

Prolonged unaccustomed exercise involving muscle lengthening (eccentric) actions can result in ultrastructural muscle disruption, impaired excitation-contraction coupling, inflammation and muscle protein degradation. This process is associated with delayed onset muscle soreness and is referred to as exercise-induced muscle damage. Although a certain amount of muscle damage may be necessary for adaptation to occur, excessive damage or inadequate recovery from exercise-induced muscle damage can increase injury risk, particularly in older individuals, who experience more damage and require longer to recover from muscle damaging exercise than younger adults. Furthermore, it is apparent that inter-individual variation exists in the response to exercise-induced muscle damage, and there is evidence that genetic variability may play a key role. Although this area of research is in its infancy, certain gene variations, or polymorphisms have been associated with exercise-induced muscle damage (i.e. individuals with certain genotypes experience greater muscle damage, and require longer recovery, following strenuous exercise). These polymorphisms include ACTN3 (R577X, rs1815739), TNF (-308 G>A, rs1800629), IL6 (-174 G>C, rs1800795), and IGF2 (ApaI, 17200 G>A, rs680). Knowing how someone is likely to respond to a particular type of exercise could help coaches/practitioners individualise the exercise training of their athletes/patients, thus maximising recovery and adaptation, while reducing overload-associated injury risk. The purpose of this review is to provide a critical analysis of the literature concerning gene polymorphisms associated with exercise-induced muscle damage, both in young and older individuals, and to highlight the potential mechanisms underpinning these associations, thus providing a better understanding of exercise-induced muscle damage.

Applied sport science of rugby league

Rugby league is a team sport in which players engage in repeated high-intensity exercise involving frequent collisions. Recent research, much of which has involved global positioning system (GPS) technology, has provided coaches and sport scientists with a deeper understanding of match demands, particularly at the elite level. This has allowed for the development of training programmes that prepare players for the most intense contact and running demands likely to be experienced in competition. At the elite level, rugby league players have well-developed aerobic and anaerobic endurance, muscular strength and power, reactive agility, and speed. Upper- and lower-body strength and aerobic power are associated with a broad range of technical and sport-specific skills, in addition to a lower risk of injury. Significant muscle damage (as estimated from creatine kinase concentrations) and fatigue occurs as a result of match-play; while muscle function and perceptual fatigue generally return to baseline 48 h following competition, increases in plasma concentrations of creatine kinase can last for up to 5 days post-match. Well-developed physical qualities may minimise post-match fatigue and facilitate recovery. Ultimately, the literature highlights that players require a broad range of physical and technical skills developed through specific training. This review evaluates the demands of the modern game, drawing on research that has used GPS technology. These findings highlight that preparing players based on the average demands of competition is likely to leave them underprepared for the most demanding passages of play. As such, coaches should incorporate drills that replicate the most intense repeated high-intensity demands of competition in order to prepare players for the worst-case scenarios expected during match-play.

Immediate and short-term effects of exercise on tendon structure: biochemical, biomechanical and imaging responses

Introduction Tendons are metabolically active structures, and their biochemical, biomechanical and structural properties adapt to chronic exercise. However, abnormal adaptations may lead to the development of tendinopathy and pain. Acute and subacute adaptations might contribute to tendon pathology. Sources of data A systematic search of peer-reviewed articles was performed using a wide range of electronic databases. A total of 61 publications were selected. Areas of agreement Exercise induces acute responses in collagen turnover, blood flow, glucose, lactate and other inflammatory products (e.g. prostaglandins and interleukins). Mechanical properties are influenced by activity duration and intensity. Acute bouts of exercise affect tendon structure, with some of the changes resembling those reported in pathological tendons. Areas of controversy Given the variation in study designs, measured parameters and outcomes, it remains debatable how acute exercise influences overall tendon properties. There is discrepancy regarding which investigation modality and settings provide optimal assessment of each parameter. Growing points There is a need for greater homogeneity between study designs, including subject consortium and age, exercise protocols and time frames for parameter assessing. Areas timely for developing research Innovative methods, measuring each parameter simultaneously, would allow a greater understanding of how and when changes occur. This methodology is key to revealing pathological processes and pathways that alter tendon properties according to various activities. Optimal tendon properties differ between activities: more compliant tendons are beneficial for slow stretch shortening cycle (SSC) activities such as countermovement jumps, whereas stiffer tendons are considered beneficial for fast SSC movements such as sprinting.

Creatine-kinase- and exercise-related muscle damage implications for muscle performance and recovery

The appearance of creatine kinase (CK) in blood has been generally considered to be an indirect marker of muscle damage, particularly for diagnosis of medical conditions such as myocardial infarction, muscular dystrophy, and cerebral diseases. However, there is controversy in the literature concerning its validity in reflecting muscle damage as a consequence of level and intensity of physical exercise. Nonmodifiable factors, for example, ethnicity, age, and gender, can also affect enzyme tissue activity and subsequent CK serum levels. The extent of effect suggests that acceptable upper limits of normal CK levels may need to be reset to recognise the impact of these factors. There is a need for standardisation of protocols and stronger guidelines which would facilitate greater scientific integrity. The purpose of this paper is to examine current evidence and opinion relating to the release of CK from skeletal muscle in response to physical activity and examine if elevated concentrations are a health concern.

Cytokines in muscle damage

Multiple cellular and molecular processes are rapidly activated following skeletal muscle damage to restore normal muscle structure and function. These processes typically involve an inflammatory response and potentially the consequent occurrence of secondary damage before their resolution and the completion of muscle repair or regeneration. The overall outcome of the inflammatory process is potentially divergent, with the induction of prolonged inflammation and further muscle damage, or its active termination and the promotion of muscle repair and regeneration. The final, detrimental, or beneficial effect of the inflammatory response on muscle repair is influenced by specific interactions between inflammatory and muscle cell-derived cytokines that act as positive and/or negative regulators to coordinate local and systemic inflammatory-related events and modulate muscle repair process. A crucial balance between proinflammatory and anti-inflammatory cytokines appears to attenuate an excessive inflammatory reaction, prevent the development of muscle fibrosis, and adequately promote the regenerative process. In this review, we address the interactive cytokine responses following muscle damage, in the context of induction and progression, or resolution of muscle inflammation and the promotion of muscle repair.

Biochemical markers of muscular damage

Muscle tissue may be damaged following intense prolonged training as a consequence of both metabolic and mechanical factors. Serum levels of skeletal muscle enzymes or proteins are markers of the functional status of muscle tissue, and vary widely in both pathological and physiological conditions. Creatine kinase, lactate dehydrogenase, aldolase, myoglobin, troponin, aspartate aminotransferase, and carbonic anhydrase CAIII are the most useful serum markers of muscle injury, but apoptosis in muscle tissues subsequent to strenuous exercise may be also triggered by increased oxidative stress. Therefore, total antioxidant status can be used to evaluate the level of stress in muscle by other markers, such as thiobarbituric acid-reactive substances, malondialdehyde, sulfhydril groups, reduced glutathione, oxidized glutathione, superoxide dismutase, catalase and others. As the various markers provide a composite picture of muscle status, we recommend using more than one to provide a better estimation of muscle stress.

Relationship between serum creatine kinase activity following exercise-induced muscle damage and muscle fibre composition

In this study, we examined the relationship between serum creatine kinase activity following exercise-induced muscle damage and muscle fibre composition. Seventeen untrained males volunteered and underwent a .[Vdot]O2max test, Wingate test, and an exercise-induced muscle damage protocol. Muscle soreness and blood samples were recorded before, immediately after, and 24, 48, 72, and 96 h after exercise. Biopsy samples from the vastus lateralis were collected one week after exercise-induced muscle damage and were assessed for muscle fibre composition. There was no significant relationship (P > 0.05) between muscle fibre composition and creatine kinase activity. A significant positive correlation (P < 0.05) was observed between soreness 48 h after exercise and type II and IIb fibres, and a significant negative correlation (P < 0.05) was observed between soreness 48 h after exercise and type I muscle fibres. Significant positive correlations were observed between soreness 48 h after exercise and the fatigue index, relative average power, and relative anaerobic capacity. Our results suggest that creatine kinase activity following exercise-induced muscle damage may not be related to muscle fibre proportions, and higher post-exercise muscular pain may be related to a predominance of type II muscle fibres and higher anaerobic capabilities.

Adenosine A(3) receptor stimulation induces protection of skeletal muscle from eccentric exercise-mediated injury

Effective therapy to reduce skeletal muscle injury associated with severe or eccentric exercise is needed. The purpose of this study was to determine whether adenosine receptor stimulation can mediate protection from eccentric exercise-induced muscle injury. Downhill treadmill exercise (-15 degrees ) was used to induce eccentric exercise-mediated skeletal muscle injury. Experiments were conducted in both normal wild-type (WT) mice and also in beta-sarcoglycan knockout dystrophic mice, animals that show an exaggerated muscle damage with the stress of exercise. In the vehicle-treated WT animals, eccentric exercise increased serum creatine kinase (CK) greater than 3-fold to 358.9 +/- 62.7 U/l (SE). This increase was totally abolished by stimulation of the A(3) receptor. In the dystrophic beta-sarcoglycan-null mice, eccentric exercise caused CK levels to reach 55,124 +/- 5,558 U/l. A(3) receptor stimulation in these animals reduced the CK response by nearly 50%. In the dystrophic mice at rest, 10% of the fibers were found to be damaged, as indicated by Evans blue dye staining. While this percentage was doubled after exercise, A(3) receptor stimulation eliminated this increase. Neither the A(1) receptor agonist 2-chloro-N(6)-cyclopentyladenosine (0.05 mg/kg) nor the A(2A) receptor agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (0.07 mg/kg) protected skeletal muscle from eccentric exercise injury in WT or dystrophic mice. The protective effect of adenosine A(3) receptor stimulation was absent in mice, in which genes for phospholipase C beta2/beta3 (PLCbeta2/beta3) and beta-sarcoglycan were deleted. The present study elucidates a new protective role of the A(3) receptor and PLCbeta2/beta3 and points to a potentially effective therapeutic strategy for eccentric exercise-induced skeletal muscle injury.

Plyometric exercise increases serum indices of muscle damage and collagen breakdown

The aim of the present study was to examine the effect of acute plyometric exercise on indices of muscle damage and collagen breakdown. Nine untrained men performed an intense bout of plyometric jumping exercises (experimental group) and nine men remained at rest (control group). Seven days before and 24, 48, and 72 hours after plyometric exercise or rest, several physiological and biochemical indices of muscle damage and two biochemical indices of collagen damage were determined. No significant changes in concentric and eccentric peak torque of knee extensors and flexors or flexion and extension range of motion were found after the plyometric exercise. Delayed-onset muscle soreness increased 48 hours after exercise. Creatine kinase increased 48 and 72 hours post exercise, whereas lactate dehydrogenase increased 24, 48, and 72 hours post exercise. Serum hydroxyproline increased 24 hours post exercise, peaked at 48 hours, and remained elevated up to 72 hours post exercise. Hydroxylysine (which was measured only before exercise and at 48 hours) was found increased 48 hours post exercise. No differences were found in any physiological or biochemical index in the control group. Intense plyometric exercise increased muscle damage, delayed-onset muscle soreness, and serum indices of collagen breakdown without a concomitant decrease in the functional capacity of muscles. Hydroxyproline and hydroxylysine levels in serum seem promising measures for describing exercise-induced collagen degradation. Coaches need to keep in mind that by using plyometric activities, despite the increased muscle damage and collagen turnover that follow, it is not necessarily accompanied by decreases in skeletal muscle capacity.

Curcumin effects on inflammation and performance recovery following eccentric exercise-induced muscle damage

Downhill running is associated with fiber damage, inflammation, delayed-onset muscle soreness, and various functional deficits. Curcumin, a constituent of the Indian spice turmeric has been investigated for its anti-inflammatory activity and may offset some of the damage and functional deficits associated with downhill running. This study examined the effects of curcumin on inflammation and recovery of running performance following downhill running in mice. Male mice were assigned to downhill placebo (Down-Plac), downhill curcumin (Down-Cur), uphill placebo (Up-Plac), or uphill curcumin (Up-Cur) groups and run on a treadmill at 22 m/min at −14% or +14% grade, for 150 min. At 48 h or 72 h after the up/downhill run, mice ( experiment 1) underwent a treadmill performance run to fatigue. Another subset of mice was placed in voluntary activity wheel cages following the up/downhill run ( experiment 2) and their voluntary activity (distance, time and peak speed) was recorded. Additional mice ( experiment 3) were killed at 24 h and 48 h following the up/downhill run, and the soleus muscle was harvested for analysis of inflammatory cytokines (IL-1β, IL-6, and TNF-α), and plasma was collected for creatine kinase analysis. Downhill running decreased both treadmill run time to fatigue (48 h and 72 h) and voluntary activity (24 h) ( P < 0.05), and curcumin feedings offset these effects on running performance. Downhill running was also associated with an increase in inflammatory cytokines (24 h and 48 h) and creatine kinase (24 h) ( P < 0.05) that were blunted by curcumin feedings. These results support the hypothesis that curcumin can reduce inflammation and offset some of the performance deficits associated with eccentric exercise-induced muscle damage.

Effects of stretching on passive muscle tension and response to eccentric exercise

BACKGROUND

Stretching is used in an attempt to improve performance and reduce the risk of muscle injury, with little evidence to support its effectiveness.

HYPOTHESIS

Four weeks of static or ballistic stretching can attenuate the increased soreness and decreased flexibility seen after eccentric exercise.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-nine male subjects were randomly assigned to a static stretching, ballistic stretching, or control group. On each of 4 consecutive days, they completed 4 maximal range of motion stretches using a Cybex isokinetic dynamometer to passively stretch the hamstrings at 0.087 rad.s(-1) (5 deg.s(-1)). Stiffness from 0.87 to 1.48 rad (50 degrees -85 degrees ), peak range of motion, work absorption, peak resistive torque, and soreness were measured. Participants then completed 4 weeks of either static or ballistic stretching for a total stretching duration of 3600 seconds. After training, the 4 days of testing were repeated with an eccentric exercise task added after day 1.

RESULTS

Stretching groups had an increase in range of motion and stretch tolerance after 4 weeks of stretching, with no change in muscle stiffness, work absorption, or delayed onset muscle soreness. After eccentric exercise, they also had greater range of motion and stretch tolerance than did controls.

CONCLUSION

Both static stretching and ballistic stretching increase range of motion, most likely as a result of enhanced stretch tolerance rather than changes in muscle elasticity. Four weeks of stretching maintain range of motion and stretch tolerance in the days after eccentric exercise.

Short vs. long length of rectus femoris during eccentric exercise in relation to muscle damage in healthy males

BACKGROUND

We investigated the effects of short vs. long length of rectus femoris during eccentric exercise of similar range of motion on selected muscle damage indicators.

METHODS

Using an isokinetic dynamometer at 1.05 rad/s, 12 healthy male [mean (standard deviation), 21 (2) years] volunteers randomly underwent two exercise sessions, one on each leg, 14 days apart. During each session, subjects had to accomplish 12 sets of 10 maximal voluntary efforts in seated and prone positions to achieve short and long length of rectus femoris, respectively. Muscle damage indicators [serum creatine kinase activity, delayed onset muscle soreness, range of motion, eccentric peak torque, concentric peak torque and isometric peak torque] were assessed pre-exercise and 24, 48, 72 as well as 96 h post-exercise.

FINDINGS

Compared to baseline data, creatine kinase, delayed onset muscle soreness, and range of motion disclosed significant changes at all time points after both exercise sessions (P<0.05). However, these muscle damage indicators demonstrated greater changes following exercise at short compared to long length of rectus femoris (P<0.05). Torque assessments also revealed that nine out of 12 and only two out of 12 measurements decreased significantly following short and long length eccentric exercise of rectus femoris, respectively (P<0.05). Short length eccentric exercise resulted in greater torque declines compared to long length during concentric and isometric evaluations (P<0.05). No such differences were observed when torque changes were evaluated eccentrically.

INTERPRETATION

Short length of rectus femoris eccentric exercise induces greater muscle damage and peak torque declines than the corresponding long length in healthy adults.

Enhanced procollagen processing in skeletal muscle after a single bout of eccentric loading in humans

Increases in procollagen processing within skeletal muscle have previously been reported in small animal models only. While indirect measurements in humans have suggested an increase procollagen processing, no intra-skeletal muscle measurements have confirmed these findings. In this study, eight young healthy male subjects performed a single bout of unaccustomed high intensity eccentric exercise on one leg, with the contralateral leg being the control. A significant increase in the muscle interstitial concentration of the N-terminal propeptide of procollagen type I (PINP) was observed (day 0: 1.96 +/- 0.44 ng ml(-1), day 2: 1.94 +/- 0.32 ng ml(-1), day 4: 3.90 +/- 1.03 ng ml(-1), day 8: 7.23 +/- 2.34 ng ml(-1)*, *P < 0.05 vs. basal and control) with no change being noted in the control leg. By day 2 post-exercise, an increase in the histological immunoreactivity of PINP and the N-terminal propeptide of procollagen type III (PIIINP) was also shown in the exercising leg only. Further, from day 2 post-exercise, immunoreactivity for tenascin C and reactive macrophages (CD68+ cells) was seen within the perimysial and endomysial connective tissue of the exercising leg only, indicating a high mechanical load and inflammation. This study shows that following a single bout of high intensity eccentric exercise there is an increase in procollagen processing within skeletal muscle in humans.

Neuromuscular function after exercise-induced muscle damage: theoretical and applied implications

Exercise-induced muscle damage is a well documented phenomenon particularly resulting from eccentric exercise. When eccentric exercise is unaccustomed or is performed with an increased intensity or duration, the symptoms associated with muscle damage are a common outcome and are particularly associated with participation in athletic activity. Muscle damage results in an immediate and prolonged reduction in muscle function, most notably a reduction in force-generating capacity, which has been quantified in human studies through isometric and dynamic isokinetic testing modalities. Investigations of the torque-angular velocity relationship have failed to reveal a consistent pattern of change, with inconsistent reports of functional change being dependent on the muscle action and/or angular velocity of movement. The consequences of damage on dynamic, multi-joint, sport-specific movements would appear more pertinent with regard to athletic performance, but this aspect of muscle function has been studied less often. Reductions in the ability to generate power output during single-joint movements as well as during cycling and vertical jump movements have been documented. In addition, muscle damage has been observed to increase the physiological demand of endurance exercise and to increase thermal strain during exercise in the heat. The aims of this review are to summarise the functional decrements associated with exercise-induced muscle damage, relate these decrements to theoretical views regarding underlying mechanisms (i.e. sarcomere disruption, impaired excitation-contraction coupling, preferential fibre type damage, and impaired muscle metabolism), and finally to discuss the potential impact of muscle damage on athletic performance.

Angle-specific impairment of elbow flexors strength after isometric exercise at long muscle length

In this study, we examined the long-term reductions in maximal isometric force (MIF) caused by a protocol of repeated maximal isometric contractions at long muscle length. Furthermore, we wished to ascertain whether the reductions in MIF are dependent on muscle length--that is, are the reductions in MIF more pronounced when the muscle contracts at a short length. The MIF of the elbow flexors of seven young male volunteers was measured at five different elbow angles between 50 degrees and 160 degrees. On a separate day, the participants performed 50 maximal voluntary isometric muscle contractions with the elbow flexors at a lengthened position; that is, with the shoulder hyperextended at 45 degrees and the elbow joint fixed at 140 degrees. Following this exercise, the MIF at the five elbow angles, range of motion, muscle soreness and plasma creatine kinase activity were measured at 24 h intervals for 4 days. On day 1, the decline in MIF was higher at the more acute elbow angles of 50 degrees (42 +/- 8%) and 70 degrees (39 +/- 8%; both P<0.01) than at 90 degrees (26 +/- 4%) and 140 degrees (16 +/- 3%; both P<0.01). No significant reduction in MIF was evident at an elbow angle of 160 degrees. Maximal isometric force at an elbow angle of 140 degrees was fully restored on day 3, whereas at an angle of 50 degrees it remained depressed for the 4 day observation period. Restoration of MIF was a function of the elbow angle, with force recovery being less at the smaller angles. The range of motion was decreased by 14 +/- 2 degrees on day 1 (P<0.01) and did not return to baseline values by day 4. Muscle soreness ratings remained significantly elevated for the 4 day period. Serum creatine kinase peaked on day 1 (522 +/- 129 IU, P<0.01) and decreased thereafter. We conclude that the disproportionate decrease in MIF at the small elbow angles and the length-specific recovery in MIF after repeated maximal isometric contractions at long muscle length may be explained by the presence of overstretched sarcomeres that increased in series compliance of the muscle, therefore causing a rightward shift of the force-length relationship.

Functional changes of human quadriceps muscle injured by eccentric exercise

The present study evaluated functional changes of quadriceps muscle after injury induced by eccentric exercise. Maximal isometric torque of quadriceps and the surface electromyography (root mean square, RMS, and median frequency, MDF) of the vastus medialis oblique (VMO) and vastus lateralis (VL) muscles were examined before, immediately after and during the first 7 days after injury. Serum creatine kinase (CK) levels and magnetic resonance imaging (MRI) were used to identify muscle injury. The subject was used as her own control and percent refers to pre-injury data. Experiments were carried out with a sedentary 23-year-old female. Injury was induced by 4 bouts of 15 maximal isokinetic eccentric contractions (angular velocity of 5 /s; range of motion from 40 to 110 of knee flexion). The isometric torque of the quadriceps (knee at 90 flexion) decreased 52% immediately after eccentric exercise and recovered on the 5th day. The highest reduction of RMS occurred on the 2nd day after injury in both VL (63%) and VMO (66%) and only VL recovered to the pre-injury level on the 7th day. Immediately after injury, the MDF decreased by 5 and 3% (VMO and VL, respectively) and recovered one day later. Serum CK levels increased by 109% on the 2nd day and were still increased by 32% on the 7th day. MRI showed large areas of injury especially in the deep region of quadriceps. In conclusion, eccentric exercise decreased the isometric torque and electromyographic signals of quadriceps muscle, which were recovered in one week, despite the muscle regeneration signals.

Effects of warm-up before eccentric exercise on indirect markers of muscle damage

PURPOSE

To test whether active and passive warm-up conducted before eccentric exercise attenuates clinical markers of muscle damage.

METHODS

Untrained subjects were exposed to one of five conditions: low-heat passive warm-up (N = 10), high-heat passive warm-up (N = 4), or active warm-up (N = 9), preceding eccentric exercise; eccentric exercise without warm-up (N = 10); or high-heat passive warm-up without eccentric exercise (N = 10). Passive warm-up of the elbow flexors was achieved using pulsed short-wave diathermy, and active warm-up was achieved by concentric contraction. Creatine kinase (CK) activity, strength, range of motion, swelling, and muscle soreness were observed before treatment (baseline) and 24, 48, 72, and 168 h after treatment.

RESULTS

High-heat passive warm-up without eccentric exercise did not affect any marker of muscle damage and was used as our control group. Markers of muscle damage were not different between groups that did or did not conduct warm-up before eccentric exercise. The active warm-up and eccentric groups exhibited a greater circumferential increase than controls (P < 0.0002), however, that was not observed after passive warm-up. Additionally, the active warm-up group exhibited a greater CK response than controls at 72 h (P < 0.05). The high-heat passive warm-up before eccentric exercise group exhibited significant change from controls at the least number of time points, but due to a small sample size (N = 4), these data should be viewed as preliminary.

CONCLUSION

Our observations suggest that passive warm-up performed before eccentric exercise may be more beneficial than active warm-up or no warm-up in attenuating swelling but does not prevent, attenuate, or resolve more quickly the other clinical symptoms of eccentric muscle damage as produced in this study.

Use of plasma creatine kinase pharmacokinetics to estimate the amount of excercise-induced muscle damage in Beagles

OBJECTIVE

To assess the effects of moderate exercise on plasma creatine kinase (CK) pharmacokinetics and to estimate exercise-induced muscle damage in dogs.

ANIMALS

6 untrained adult Beagles.

PROCEDURE

The study was divided into 3 phases. In phase 1, dogs ran for 1 hour at a speed of 9 km/h, and samples were used to determine the area under the plasma CK activity versus time curve (AUC) induced by exercise. In phases 2 and 3, pharmacokinetics of CK were calculated in dogs during exercise and at rest, respectively. Values for AUC and plasma clearance (CI) were used to estimate muscle damage.

RESULTS

At rest, values for Cl, steady-state volume of distribution (Vdss), and mean retention time (MRT) were 0.32+/-0.02 ml/kg of body weight/min, 57+/-173 ml/kg, and 3.0+/-0.57 h, respectively. During exercise, Cl decreased significantly (0.26+/-0.03 ml/kg/min), MRT increased significantly, (4.4+/-0.97 h), and Vdss remained unchanged. Peak of plasma CK activity (151+/-58.8 U/L) was observed 3 hours after completion of exercise. Estimated equivalent amount of muscle corresponding to the quantity of CK released was 41+/-29.3 mg/kg.

CONCLUSION AND CLINICAL RELEVANCE

These results revealed that exercise had a minor effect on CK disposition and that the equivalent amount of muscle damaged by moderate exercise was negligible. This study illustrates the relevance for use of the minimally invasive and quantitative pharmacokinetic approach when estimating muscle damage.

Continuous Compression as an Effective Therapeutic Intervention in Treating Eccentric-Exercise-Induced Muscle Soreness

Context:

Prior investigations using ice, massage, or exercise have not shown efficacy in relieving delayed-onset muscle soreness.

Objectives:

To determine whether a compression sleeve worn immediately after maximal eccentric exercise enhances recovery.

Design:

Randomized, controlled clinical study.

Setting:

University sports medicine laboratory.

Participants:

Fifteen healthy, non-strength-trained men, matched for physical criteria, randomly placed in a control group or a continuous compression-sleeve group (CS).

Methods and Measures:

Subjects performed 2 sets of 50 arm curls. 1RM elbow flexion at 60°/s, upper-arm circumference, resting-elbow angle, serum creatine kinase (CK), and perception-of-soreness data were collected before exercise and for 3 days.

Results:

CK was significantly (P< .05) elevated from the baseline value in both groups, although the elevation in the CS group was less. CS prevented loss of elbow extension, decreased subjects’ perception of soreness, reduced swelling, and promoted recovery of force production.

Conclusions:

Compression is important in soft-tissue-injury management.

Force and EMG power spectrum during and after eccentric and concentric fatigue

Eccentric and concentric force and median frequency of the EMG power spectrum were measured during and immediately after maximal eccentric (EE) and concentric (CE) exercise and during the recovery period of 1 week. Eight male subjects performed EE and CE consisting of 100 maximal eccentric and concentric actions with elbow flexors during two separate exercise sessions. When comparing maximal eccentric and concentric actions before the exercises, the average force was higher (P<0.001) in eccentric than in concentric but the average rectified EMG (aEMG) values were the same with the two types of action. The average eccentric force decreased 53.3% after EE and 30.6% after CE, while the average concentric force decreased 49.9% after CE and 38.4% after EE. The recovery was slower after EE. The median frequency (MF) of biceps brachii (BB) in eccentric action decreased during both EE (P<0.01) and CE (P<0.05). It recovered within 2 days of the exercises but was lower again (P<0.01) 7 days after EE. In concentric action MF of BB decreased during CE (P<0.01), while no changes were observed in EE. Blood lactate concentration increased (P<0.001) in both exercises and serum creatine kinase (CK) activity increased in EE only, being significantly higher (P<0.001) 7 days after than before the eccentric exercise. In the absolute scale, the eccentric force in EE decreased more than the concentric force in CE (P<0.01). Fatigue response was action type specific as seen in the greater reduction in the force of the exercise type. MF decreased immediately after both exercises, which may be at least partly related to elevated blood lactate concentration. Eccentric actions led to possible muscle damage as indicated by elevated serum CK and muscle soreness, and therefore to longer recovery as compared to concentric actions. Decreased MF after EE may be indicative of selective damage of the fast twitch fibers in this type of exercise.