Effects of step exercise on muscle damage and muscle Ca2+ content in men and women

Skeletal muscle myosin heavy chain protein fragmentation as a potential marker of protein degradation in response to resistance training and disuse atrophy

We sought to examine how resistance exercise (RE), cycling exercise, and disuse atrophy affect myosin heavy chain (MyHC) protein fragmentation in humans. In the first study (1boutRE), younger adult men (n=8; 5±2 years of RE experience) performed a lower body RE bout with vastus lateralis (VL) biopsies obtained immediately before, 3-, and 6-hours post-exercise. In the second study (10weekRT), VL biopsies were obtained in untrained younger adults (n=36, 18 men and 18 women) before and 24 hours (24h) after their first/naïve RE bout. These participants also engaged in 10 weeks (24 sessions) of resistance training and donated VL biopsies before and 24h after their last RE bout. VL biopsies were also examined from a third acute cycling study (n=7) and a fourth study involving two weeks of leg immobilization (n=20, 15 men and 5 women) to determine how MyHC fragmentation was affected. In the 1boutRE study, the fragmentation of all MyHC isoforms (MyHCTotal) increased 3 hours post-RE (~ +200%, p=0.018) and returned to pre-exercise levels by 6 hours post-RE. Immunoprecipitation of MyHCTotal revealed ubiquitination levels remained unaffected at the 3- and 6-hour post-RE time points. Interestingly, a greater increase in magnitude for MyHC type IIa versus I isoform fragmentation occurred 3-hours post-RE (8.6±6.3-fold versus 2.1±0.7-fold, p=0.018). In all 10weekRT participants, the first/naïve and last RE bouts increased MyHCTotal fragmentation 24h post-RE (+65% and +36%, respectively; p<0.001); however, the last RE bout response was attenuated compared to the first bout (p=0.045). The first/naïve bout response was significantly elevated in females only (p<0.001), albeit females also demonstrated a last bout attenuation response (p=0.002). Although an acute cycling bout did not alter MyHCTotal fragmentation, ~8% VL atrophy with two weeks of leg immobilization led to robust MyHCTotal fragmentation (+108%, p<0.001), and no sex-based differences were observed. In summary, RE and disuse atrophy increase MyHC protein fragmentation. A dampened response with 10 weeks of resistance training, and more refined responses in well-trained men, suggest this is an adaptive process. Given the null polyubiquitination IP findings, more research is needed to determine how MyHC fragments are processed. Moreover, further research is needed to determine how aging and disease-associated muscle atrophy affect these outcomes, and whether MyHC fragmentation is a viable surrogate for muscle protein turnover rates.

The effect of lesser mealworm protein on exercise-induced muscle damage in active older adults: a randomized controlled trial

OBJECTIVES

We compared the effect of 12 weeks lesser mealworm-based (Alphitobius diaperinus) protein supplementation to whey protein and placebo supplementation on Exercise-Induced Muscle Damage (EIMD) after long-distance walking in older adults.

METHODS

in this randomized controlled trial, 70 physically active older adults (>60 years) were randomly allocated to the following groups: I) lesser mealworm protein, II) whey protein or III) iso-caloric placebo. Participants received supplements 11 weeks before and 1 week during a 3-day long-distance walking challenge (30-50 km per day). Blood concentrations of creatinine kinase (CK) and lactate dehydrogenase (LDH), handgrip strength and muscle soreness were measured pre-exercise and directly after each walking bout.

RESULTS

Significant elevations of CK concentrations (103 [76-161] U/l to 758 [342-1104] U/l, p < 0.001) and LDH concentrations (202 [175-220] to 283 [252-339] U/l, p < 0.001) were observed following 7h45 min ± 11 min of walking exercise per day, but the magnitude of this effect did not differ among suppletion groups. Hand grip strength decreased significantly (p < 0.001) while muscle soreness increased (p = 0.002) after the first walking day compared to pre-exercise, with no group differences.

CONCLUSION

12-weeks of lesser mealworm-based protein supplementation (30 g/day) does not attenuate exercise induced muscle damage in older adults following three days of prolonged walking exercise in comparison to placebo or whey protein.

Impacts of altered exercise volume, intensity, and duration on the activation of AMPK and CaMKII and increases in PGC-1α mRNA

The purpose of this review is to explore and discuss the impacts of augmented training volume, intensity, and duration on the phosphorylation/activation of key signaling protein - AMPK, CaMKII and PGC-1α - involved in the initiation of mitochondrial biogenesis. Specifically, we explore the impacts of augmented exercise protocols on AMP/ADP and Ca²⁺ signaling and changes in post exercise PGC - 1α gene expression. Although AMP/ADP concentrations appear to increase with increasing intensity and during extended durations of higher intensity exercise AMPK activation results are varied with some results supporting and intensity/duration effect and others not. Similarly, CaMKII activation and signaling results following exercise of different intensities and durations are inconsistent. The PGC-1α literature is equally inconsistent with only some studies demonstrating an effect of intensity on post exercise mRNA expression. We present a novel meta-analysis that suggests that the inconsistency in the PGC-1α literature may be due to sample size and statistical power limitations owing to the effect of intensity on PGC-1α expression being small. There is little data available regarding the impact of exercise duration on PGC-1α expression. We highlight the need for future well designed, adequately statistically powered, studies to clarify our understanding of the effects of volume, intensity, and duration on the induction of mitochondrial biogenesis by exercise.

Sex differences in the impact of resistance exercise load on muscle damage: A protocol for a randomised parallel group trial

Introduction

Resistance training can induce skeletal muscle hypertrophy and strength gains, but is also associated with acute muscle damage, characterised by muscle soreness, impaired muscle function, and structural damage to muscle cell membranes and its components. These consequences can be detrimental to future exercise performance and dampen long-term training adaptations. Previous research has considered resistance exercise intensity as a factor in exercise-induced muscle damage (EIMD), though a clear direction of the findings has not yet been established. Further, female populations are heavily underrepresented in this field of study. Therefore, we here propose a study protocol designed to examine sex differences in the muscle damage response to resistance exercise performed with low or high loads in a population of untrained, young adults.

Methods

This study will employ a randomised parallel group design. Twenty-four males and 24 females will perform an acute leg-based resistance exercise session at either 30% (low-load) or 80% (high-load) of their pre-determined one-repetition maximum (1RM). Maximal leg strength will be determined by a 1RM test 3 wk before and 72 and 168 h after the exercise bout. Additionally, muscle damage will be assessed immediately before the exercise bout and immediately, 24, 48, 72, and 168 h after the exercise bout through measures of muscle soreness, limb circumference, range of motion, and serum concentrations of creatine kinase and interleukin-6. The outcomes of this trial could inform sex-specific resistance training recommendations and help bridge the sex data gap in sport and exercise science research.

American Ginseng Attenuates Eccentric Exercise-Induced Muscle Damage via the Modulation of Lipid Peroxidation and Inflammatory Adaptation in Males

Exercise-induced muscle damage (EIMD) is characterized by a reduction in functional performance, disruption of muscle structure, production of reactive oxygen species, and inflammatory reactions. Ginseng, along with its major bioactive component ginsenosides, has been widely employed in traditional Chinese medicine. The protective potential of American ginseng (AG) for eccentric EIMD remains unclear. Twelve physically active males (age: 22.4 ± 1.7 years; height: 175.1 ± 5.7 cm; weight: 70.8 ± 8.0 kg; peak oxygen consumption [V˙O2peak] 54.1 ± 4.3 mL/kg/min) were administrated by AG extract (1.6 g/day) or placebo (P) for 28 days and subsequently challenged by downhill (DH) running (−10% gradient and 60% V˙O2peak). The levels of circulating 8-iso-prostaglandin F 2α (PGF2α), creatine kinase (CK), interleukin (IL)-1β, IL-4, IL-10, and TNF-α, and the graphic pain rating scale (GPRS) were measured before and after supplementation and DH running. The results showed that the increases in plasma CK activity induced by DH running were eliminated by AG supplementation at 48 and 72 h after DH running. The level of plasma 8-iso-PGF2α was attenuated by AG supplementation immediately (p = 0.01 and r = 0.53), 2 h (p = 0.01 and r = 0.53) and 24 h (p = 0.028 and r = 0.45) after DH running compared with that by P supplementation. Moreover, our results showed an attenuation in the plasma IL-4 levels between AG and P supplementation before (p = 0.011 and r = 0.52) and 72 h (p = 0.028 and r = 0.45) following DH running. Our findings suggest that short-term supplementation with AG alleviates eccentric EIMD by decreasing lipid peroxidation and promoting inflammatory adaptation.

Sex-Related Differences After a Single Bout of Maximal Eccentric Exercise in Response to Acute Effects: A Systematic Review and Meta-analysis

Morawetz, D, Blank, C, Koller, A, Arvandi, M, Siebert, U, and Schobersberger, W. Sex-related differences after a single bout of maximal eccentric exercise in response to acute effects: a systematic review and meta-analysis. J Strength Cond Res 34(9): 2697-2707, 2020-The most prominent effects after unaccustomed eccentric exercise are muscle damage, muscle soreness, strength loss, and higher concentrations of muscle proteins in the plasma. The aim of this systematic review is to evaluate sex-related differences in these acute effects. A systematic literature search in MEDLINE following the PRISMA guidelines was performed. Inclusion criteria were the difference in absolute outcomes between sexes in eccentric muscle strength, strength loss after eccentric exercise, blood concentrations of creatine kinase (CK), and delayed onset muscle soreness (DOMS). Results for maximal eccentric torque and CK data were pooled using a random-effect meta-analysis. A meta-regression was conducted to explain heterogeneity. Based on the 23 included trials, men showed significantly higher absolute eccentric strength. No sex-related differences were detected when normalizing strength for body mass, cross-sectional area of the muscle, or fat-free mass. Women displayed a tendency toward greater relative strength loss immediately after exercise. The absolute CK concentrations of men were significantly higher after exercise-induced muscle damage. No significant difference was found between sexes in DOMS. Untrained men and women display similar responses in all measures of relative muscle strength and DOMS. Apart from the enzymatic activity after exercise and the levels of absolute eccentric torque, there is no evidence for sex-related differences immediately after eccentric exercise. Therefore, eccentric training might have the same impact on men and women. One potential sex difference with practical relevance would be the possible difference in fatigue pattern immediately after eccentric exercise.

Impact of physical activity on monocyte subset CCR2 expression and macrophage polarization following moderate intensity exercise

Coronary artery disease (CAD) is an immune-mediated disease in which CCR2 attracts classical, intermediate, and non-classical monocytes to the arterial intima where they differentiate to macrophages. Balance between pro-inflammatory M1 and anti-inflammatory M2 macrophages contributes to CAD prevention. Moderate to vigorous intensity physical activity (MVPA) elicits an immune response and reduces the incidence of CAD, however, the impact of prior MVPA on monocyte subset CCR2 expression and macrophage polarization following acute exercise is unknown.

Purpose

To determine the impact of physical activity status on monocyte subset CCR2 surface expression and macrophage polarization in response to an acute bout of moderate intensity cycle ergometry.

Methods

24 healthy women and men (12 high physically active [HIACT]: ≥1500 METmin/wk MVPA & 12 low physically active [LOACT]: <600 METmin/wk MVPA) underwent an acute moderate intensity (60% VO2peak) bout of cycle ergometry for 30 ​min. Blood samples were collected prior to (PRE), immediately (POST), 1 ​h (1H), and 2 ​h (2H) following exercise. Monocyte CCR2 and macrophage CD86 (M1) and CD206 (M2) were analyzed by flow cytometry.

Results

Intermediate monocyte CCR2 decreased in response to exercise in the HIACT group (PRE: 11409.0 ​± ​1084.0 vs. POST: 9524.3 ​± ​1062.4; p ​= ​0.034). Macrophage CD206 was lower in the LOACT compared to the HIACT group at 1H (HIACT: 67.2 ​± ​5.6 vs. LOACT: 50.1 ​± ​5.2%; p ​= ​0.040). Macrophage CD206 at 1H was associated with both PRE (r ​= ​0.446, p ​= ​0.043) and POST (r ​= ​0.464, p ​= ​0.034) non-classical monocyte CCR2.

Conclusion

These data suggest that regular moderate to vigorous physical activity positively impacts both monocytes and macrophages following acute moderate intensity exercise and that this impact may contribute to the prevention of coronary artery disease.

Prevalence of Falls on Mount Fuji and Associated with Risk Factors: A Questionnaire Survey Study

Since little is known about the detailed situations of falls on Mount Fuji, the aim of this study was to clarify the risk factors of falls on Mount Fuji in Japan. We conducted a questionnaire survey of 556 participants who had climbed Mount Fuji and collected the following information: fall situation, mental status, fatigue feeling, sex, age, climbing experience on Mount Fuji and other mountains, summit success, whether staying at a lodge, use of a tour guide, and symptoms of acute mountain sickness. Among the 556 participants, 167 had a fall (30%). Among 167 participants who had experienced a fall, 30 had fallen more than three times (18%). The main cause (>60%) of fall were slips. The most optimal model using multiple logistic regression (no fall = 0, and fall = 1) found eight significant risk factors, including sex, prior climbing experience on Mount Fuji, staying overnight at a lodge, subjective feeling of relaxation, sleepiness, emotional stability, dullness, and eyestrain. These results suggest that females, people who have no prior climbing experience on Mount Fuji, and people who did not stay at a lodge should pay attention to an increased risk of falls on Mount Fuji.

Minimal Evidence for a Secondary Loss of Strength After an Acute Muscle Injury: A Systematic Review and Meta-Analysis

BACKGROUND

An immediate loss of strength follows virtually all types of muscle injury but there is debate whether the initial strength loss is maximal or if a secondary loss of strength occurs during the first 3 days post-injury.

OBJECTIVE

The objective of this analysis was to conduct a systematic review and meta-analysis of the research literature to determine if a secondary loss of strength occurs after an injurious initiating event.

METHODS

Literature searches were performed using eight electronic databases (e.g., PubMed, Cochrane Library). Search terms included skeletal muscle AND (injur* OR damage*) AND (strength OR force OR torque). The extracted strength data were converted to a standard format by calculating the standardized mean difference, which is reported as the effect size (ES) along with its 95 % confidence interval (CI). The calculation of ES was designed so that a negative ES that was statistically less than zero would be interpreted as indicating a secondary loss of strength.

RESULTS

A total of 223 studies with over 4000 human and animal subjects yielded data on 262 independent groups and a total of 936 separate ESs. Our overall meta-analysis yielded a small-to-medium, positive overall ES that was statistically greater than zero (overall ES = +0.34, 95 % CI 0.27-0.40; P < 0.00000001). Considerable variation in ES was observed among studies (I ² = 86 %), which could be partially explained by the research group conducting the study, sex of the subject, day of post-injury strength assessment, whether fatigue was present immediately post-injury, and the muscle group injured. From the subgroup meta-analyses probing these variables, 36 subgroup ESs were calculated and none were statistically less than zero.

CONCLUSION

Overall, our findings do not support the presence of a secondary loss of strength following an acute muscle injury, and strongly suggest that strength, on average, recovers steadily over the first 3 days post-injury.

Gender differences in residual effect of prior drop jumps on oxygen uptake during heavy cycling exercise

BACKGROUND AND OBJECTIVE

Unaccustomed eccentric or eccentric-concentric exercise leaves us stiff and sore the next day and can cause muscle damage. The data about the residual effect of prior eccentric-concentric exercises on oxygen uptake (VO₂) during constant cycling exercise in women or the data about differences of such effect between genders are scarce. Therefore, the aim of this study was to assess differences of the residual effect of PDJ on VO₂ during HCE and indirect muscle damage parameters between women and men.

MATERIALS AND METHODS

The study aimed to asses differences of the residual effect of prior drop jumps (PDJ) on VO₂ during heavy cycling exercise (HCE) and indirect muscle damage parameters between men (n=8) and women (n=11). On four different days participants performed one incremental cycling exercise and three HCE (control [CON], 45min [45' PDJ] and 24h [24h PDJ] after 100 drop jumps). The intensity of HCE was set to work rate corresponding to 50% of the difference between the second and the first ventilatory thresholds which were determined analyzing pulmonary gas exchange parameters during incremental cycling exercise. Capillary blood samples were collected in order to measure blood lactate concentration immediately after HCE and serum creatine kinase (CK) activity 24h after PDJ. Subjects rated perceived exertion and delayed onset muscle soreness (DOMS) using 20 and 10 point scales, respectively.

RESULTS

VO₂ at 3-6min of HCE performed 45' after PDJ was significantly increased as compared to CON HCE only in the male group. Both men and women felt moderate muscle pain. CK activity was significantly increased 24h after PDJ in the male group. Both during HCE 45' PDJ and 24h PDJ, the significant positive correlation was observed between relative changes of VO₂ during steady state of HCE and CK activity only in the male group.

CONCLUSIONS

Prior eccentric-concentric exercise of thigh muscles (100 drop jumps) accelerates VO₂ kinetics at the start and increases VO₂ during steady state of heavy cycling only in the male group. So, prior exercise of such type has a higher negative impact on cycling economy in men than in women and this might be related to greater muscle damage and fatigue in physically active male persons after plyometric exercise.

Effect of Muscle-Damaging Eccentric Exercise on Running Kinematics and Economy for Running at Different Intensities

The objective of this study was to explore the changes in running kinematics and economy during running at different intensities 1 and 24 hours after a muscle-damaging bench-stepping exercise. Healthy, physically active adult women were recruited for this study. The subjects' running kinematics, heart rate, gas exchange, minute ventilation, and perceived exertion were continuously recorded during the increasing-intensity running test on a treadmill for different testing conditions: a control condition and 1 and 24 hours after the bench-stepping exercise test. Two muscle damage markers, muscle soreness and blood creatine kinase (CK) activity, were measured before and 24 hours after the stepping exercise. Muscle soreness and blood CK activity were significantly altered (exact p ≤ 0.05, Monte Carlo test) 24 hours after the bench-stepping exercise. The stride length, stride frequency, and support time at different running intensities did not change. Twenty-four hours after the previous step exercise, ankle dorsiflexion in the support phase was significantly higher during severe-intensity running, the range of knee flexion at the stance phase was significantly lower during moderate-intensity running, and knee flexion at the end of the amortization phase was significantly lower during heavy-intensity running compared with the control values (exact p ≤ 0.05, Monte Carlo test). The running economy at moderate and heavy intensities, maximum ventilation, and maximum heart rate did not change. We conclude that, given moderate soreness in the calf muscles 24 hours after eccentric exercise, the running kinematics are slightly but significantly changed without a detectable effect on running economy.

Muscle Damage following Maximal Eccentric Knee Extensions in Males and Females

Aim

To investigate whether there is a sex difference in exercise induced muscle damage.

Materials and Method

Vastus Lateralis and patella tendon properties were measured in males and females using ultrasonography. During maximal voluntary eccentric knee extensions (12 reps x 6 sets), Vastus Lateralis fascicle lengthening and maximal voluntary eccentric knee extensions torque were recorded every 10° of knee joint angle (20–90°). Isometric torque, Creatine Kinase and muscle soreness were measured pre, post, 48, 96 and 168 hours post damage as markers of exercise induced muscle damage.

Results

Patella tendon stiffness and Vastus Lateralis fascicle lengthening were significantly higher in males compared to females (p<0.05). There was no sex difference in isometric torque loss and muscle soreness post exercise induced muscle damage (p>0.05). Creatine Kinase levels post exercise induced muscle damage were higher in males compared to females (p<0.05), and remained higher when maximal voluntary eccentric knee extension torque, relative to estimated quadriceps anatomical cross sectional area, was taken as a covariate (p<0.05).

Conclusion

Based on isometric torque loss, there is no sex difference in exercise induced muscle damage. The higher Creatine Kinase in males could not be explained by differences in maximal voluntary eccentric knee extension torque, Vastus Lateralis fascicle lengthening and patella tendon stiffness. Further research is required to understand the significant sex differences in Creatine Kinase levels following exercise induced muscle damage.

The influence of estradiol on muscle damage and leg strength after intense eccentric exercise

PURPOSE

To examine the influence of estradiol on muscle damage and leg strength after intense eccentric exercise.

METHODS

Eight men (MEN), eight normally menstruating women (WomenNM), and eight women using oral contraceptives (WomenOC) participated in this study. Subjects performed 240 maximal-effort bilateral eccentric contractions of the quadriceps muscle groups designed to elicit exercise-induced muscle damage (EiMD). Serum creatine kinase (CK), myoglobin (Mb), and fatty acid-binding protein (FABP) concentrations were measured before (pre-) EiMD, as well as 0, 6, 24, and 48 h post-EiMD. Peak isometric quadriceps torque (i.e., leg strength) was measured pre-EiMD, as well as 24 and 48 h post-EiMD.

RESULTS

The increases in CK, Mb, and FABP concentrations from pre- to post-EiMD were greater in MEN (10-fold, 15-fold, and fourfold, respectively) and WomenOC (sevenfold, 11-fold, and ninefold) compared with WomenNM (five-, six-, and threefold; p < 0.05). The decline in leg strength was about 10 % pre- to 24 h post-EiMD in all groups and decreased a further 10-15 % by 48 h post-EiMD in the MEN and WomenOC only.

CONCLUSION

Our findings suggest an important role of estradiol in blunting the muscle damage response to intense eccentric exercise and preserving muscle function after EiMD.

Regenerated soleus muscle shows reduced creatine kinase efflux after contractile activity in vitro

Regenerated skeletal muscles show less muscle damage after strenuous muscle exercise. The aim of the studies was to investigate if the regeneration is associated with reduced muscle creatine kinase (CK) efflux immediately after the exercise. Cryolesion was applied to the soleus muscle of 3-month-old C57BL/6J male mice. Then total CK efflux was assessed in vitro in the regenerated muscles without exercise or after 100 eccentric contractions. The same measurements were performed in the control muscles, which were not exposed to cryolesion. Regenerated muscles generated weaker (P < 0.05) twitches, but stronger (P < 0.05) 150-Hz and 300-Hz tetani with prolonged (P < 0.01) contraction times compared with the control muscles. There was no difference between regenerated and control muscles in the total CK efflux without exercise, but only control muscles showed an increase (P < 0.001) in the CK efflux after the exercise. Our results suggest that muscle regeneration is associated with modulation of contractile properties and improvement in muscle resistance to damage after eccentric exercise.

Influence of exercise contraction mode and protein supplementation on human skeletal muscle satellite cell content and muscle fiber growth

Skeletal muscle satellite cells (SCs) are involved in remodeling and hypertrophy processes of skeletal muscle. However, little knowledge exists on extrinsic factors that influence the content of SCs in skeletal muscle. In a comparative human study, we investigated the muscle fiber type-specific association between emergence of satellite cells (SCs), muscle growth, and remodeling in response to 12 wk unilateral resistance training performed as eccentric (Ecc) or concentric (Conc) resistance training ± whey protein (Whey, 19.5 g protein + 19.5 g glucose) or placebo (Placebo, 39 g glucose) supplementation. Muscle biopsies (vastus lateralis) were analyzed for fiber type-specific SCs, myonuclei, and fiber cross-sectional area (CSA). Following training, SCs increased with Conc in both type I and type II fibers (P < 0.01) and exhibited a group difference from Ecc (P < 0.05), which did not increase. Myonuclei content in type I fibers increased in all groups (P < 0.01), while a specific accretion of myonuclei in type II fibers was observed in the Whey-Conc (P < 0.01) and Placebo-Ecc (P < 0.01) groups. Similarly, whereas type I fiber CSA increased independently of intervention (P < 0.001), type II fiber CSA increased exclusively with Whey-Conc (P < 0.01) and type II fiber hypertrophy correlated with whole muscle hypertrophy exclusively following Conc training (P < 0.01). In conclusion, isolated concentric knee extensor resistance training appears to constitute a stronger driver of SC content than eccentric resistance training while type II fiber hypertrophy was accentuated when combining concentric resistance training with whey protein supplementation.

Variable inflammation and intramuscular STAT3 phosphorylation and myeloperoxidase levels after downhill running

Individual responses in creatine kinase (CK) release after eccentric exercise are divergent. This study aimed to identify whether this could be related to selected humoral or intramuscular inflammatory factors. Twenty-three subjects were divided into non-exercising (n = 5) and downhill run (DHR; n = 18) groups (12 × 5 min, 10% decline at 15 km/h). Blood samples were analyzed for white blood cell differential count, CK, myoglobin, tumor necrosis factor-α, granulocyte colony-stimulating factor, interleukin (IL)-1β, IL-6, and IL-10. Muscle biopsies were analyzed for signal transducer and activator of transcription-3 (STAT3), IκBα, and myeloperoxidase (MPO). DHR participants clustered as early (DHR1) recovery, biphasic response (DHR2), or classic delayed exaggerated CK response (DHR3), with a delayed CK peak (4784 ± 1496 U/L) on day 4. For DHR1 and DHR2, CK peaked on day 1 (DHR1: 1198 ± 837 U/L) or on day 1 and day 4 (DHR2: 1583 ± 448 U/L; 1878 ± 427 U/L), respectively. Immediately post-DHR, IL-6 increased in DHR2 and DHR3 whereas IL-10 increased in all DHR groups. STAT3 signaling increased for DHR1 and DHR2 at 4 h, but MPO at day 2 only in DHR2. Objective cluster analysis uncovered a group of subjects with a characteristic biphasic CK release after DHR. The second elevation was related to their early cytokine response. The results provide evidence that early responses following eccentric exercise are indicative of later variation.

Concomitant changes in cross-sectional area and water content in skeletal muscle after resistance exercise

This study investigated how one bout (1EX) and three bouts (3EX) of strenuous resistance exercise affected the cross-sectional area (CSA) and water content (WC) of the quadriceps muscle and patella tendon (PT), 4 h and 52 h after the last exercise bout. Ten healthy untrained male subjects performed 1EX with one leg and 3EX with the other leg. CSA and WC were measured with magnetic resonance imaging 10, 20 and 30 cm proximal to the tibia plateau (TP) for the muscle, and at the proximal, central and distal site for the PT prior to exercise, and 4 h and 52 h after the last exercise bout. Ten centimeter above the TP, muscle CSA was significantly increased at 4 h (1EX: 13 ± 5%; 3EX: 13 ± 4%) and 52 h (1EX: 16 ± 5%; 3EX: 16 ± 5%) compared with baseline. Muscle WC was significantly increased at 4 h (1EX: 7 ± 1%; 3EX: 6 ± 2%) and 52 h (1EX: 8 ± 2%; 3EX: 8 ± 3%) compared to baseline. PT central CSA was significantly reduced at 52 h (3EX: 14 ± 2%) compared with baseline and (3EX: 13 ± 1%) compared with 4 h. Present data demonstrate that strenuous resistance exercise results in an acute increase in muscle WC and underlines the importance of ensuring sufficient time between the last exercise bout and the determination of anatomical dimensions in muscles.

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.

Effects of flexibility training on eccentric exercise-induced muscle damage

PURPOSE

This study investigated whether flexibility training would attenuate muscle damage induced by maximal eccentric exercise.

METHODS

Thirty untrained young men were allocated to static stretching (SS), proprioceptive neuromuscular facilitation (PNF), or control group (n = 10 per group). The SS consisted of 30 sets of a 30-s standard SS with a 30-s rest between sets, and the PNF included 5 sets of the 30-s standard SS followed by 3 sets of three "contract-relax-agonist-contract" procedures. These were performed three times a week for 8 wk, and all subjects performed six sets of 10 maximal isokinetic (30°·s) lengthening contractions of the knee flexors after the 8-wk training or 8 wk after the baseline measures (control). Changes in indirect markers of muscle damage before and for 5 d after the eccentric exercise were compared among the groups.

RESULTS

The range of motion (ROM) of the hip joint increased by 25°, and the optimum angle of the knee flexors shifted (P < 0.05) to a longer muscle length by 10° after training, without significant differences between SS and PNF. No significant changes in these variables were evident for the control group. Compared with the control group, the SS and PNF groups showed significantly (P < 0.05) smaller decreases and faster recovery of knee flexor muscle strength and smaller changes in optimum angle, ROM, muscle soreness, and plasma creatine kinase activity and myoglobin concentration without significant differences between the groups. The preeccentric exercise ROM or optimum angle was significantly (P < 0.05) correlated with the changes in the muscle damage markers.

CONCLUSIONS

These results suggest that both SS and PNF training are effective in attenuating eccentric exercise-induced muscle damage and that flexible muscles are less susceptible to the damage.

Heat shock protein translocation and expression response is attenuated in response to repeated eccentric exercise

AIM

This study hypothesized that heat shock protein (HSP) translocation and upregulation is more probable to occur after eccentric exercise than after concentric exercise or repeated eccentric exercise.

METHODS

Fourteen young, healthy, untrained male subjects completed two bench-stepping exercise bouts with 8 weeks between bouts, and were compared with a control group (n = 6). Muscle biopsies collected from m. vastus lateralis of both legs prior to and at 3 h, 24 h and 7 days after exercise were quantified for mRNA levels and/or for HSP27, alphabeta-crystallin and inducible HSP70 content in cytosolic and cytoskeletal protein fractions.

RESULTS

The first bout of exercise reduced muscle strength and increased muscle soreness predominantly in the eccentric leg (P < 0.05). These responses were attenuated after the repeated eccentric exercise bout (P < 0.05), suggesting a repeated bout adaptation. Increases in inducible HSP70 and HSP27 protein content in cytoskeletal fractions were observed exclusively after eccentric exercise (P < 0.05). For HSP27, an approx. 10-fold upregulation after first-bout eccentric exercise was attenuated to a an approximately fourfold upregulation after the repeated eccentric exercise bout. mRNA levels for HSP70, HSP27 and alphabeta-crystallin were upregulated within approximately two to fourfold ranges at time points 3 and 24 h post-exercise (P < 0.05). This upregulation was induced exclusively by eccentric exercise but with a tendency to attenuated expression 3 h after the repeated eccentric exercise bout.

CONCLUSION

Our results show that HSP translocation and expression responses are induced by muscle damaging exercise, and suggest that such HSP responses are closely related to the extent of muscle damage.