Bout Of Maximal Eccentric Exercise Research Articles

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.

Shear-wave velocity of the patellar tendon and quadriceps muscle is increased immediately after maximal eccentric exercise

To determine whether stiffness of the patellar tendon and quadriceps muscles is altered immediately after and 48h after a single bout of maximal eccentric exercise of the knee extensor muscles. Thirteen healthy individuals [group mean (SD) age 22.4 (3.5) years; 7 female] performed a single bout of maximal eccentric exercise of the non-dominant knee extensors, using an isokinetic dynamometer. Shear-wave velocity (an index of tissue stiffness) was recorded from the patellar tendon, vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL), before, following (post0), and 48 h after (post48) exercise. To investigate features of exercise induced muscle damage, maximal voluntary isometric contraction (MVIC) and self-reported pain and stiffness (numerical rating scales 0 = no pain/stiffness to 100 = worst imaginable pain/stiffness) were measured before, post0, and post48 exercise. Serum creatine kinase (CK) was measured before and post48 exercise. Compared to preexercise, MVIC decreased and self-reported pain and stiffness increased at post0 and post48 and CK levels increased at post48 (all p < 0.01). Compared to preexercise, shear-wave velocity was greater at post0 for the patellar tendon [15.9 (24.6)%, p = 0.01] and RF [23.6 (16.7)%, p < 0.001], each returning to baseline by post48. No significant differences were observed for VL or VM post0 or post48 exercise. Maximal eccentric exercise produced an immediate increase in the stiffness of the patellar tendon and RF, resolving by 48 h. As this change was not observed in VL and VM, future studies may explore heterogeneity within synergist muscles following eccentric exercise.

Acute Response of PGC-1α and IGF-1 Isoforms to Maximal Eccentric Exercise in Skeletal Muscle of Postmenopausal Women.

PGC-1α4, a novel isoform of the transcriptional coactivator PGC-1α, was recently postulated to modulate the expression of anabolic and catabolic genes and therefore regulate skeletal muscle hypertrophy. Resting levels of PGC-1α4 messenger RNA (mRNA) expression were found to increase in healthy adults after resistance training. However, the acute effect of resistance exercise (RE) on PGC-1α4 expression in populations prone to progressive muscle loss, such as postmenopausal women, has not been evaluated. Here, we investigated alterations in mRNA expression of PGC-1α4 and PGC-1α1, a regulator of muscle oxidative changes, in postmenopausal women after high-intensity eccentric RE and analyzed these findings with respect to changes in insulin-like growth factor (IGF)-1 and catabolic gene expression. Nine postmenopausal women (age, 57.9 ± 3.2 years) performed 10 sets of 10 maximal eccentric repetitions of single-leg extension with 20-second rest periods between sets. Muscle biopsies were obtained from the vastus lateralis of the exercised leg before and 4 hours after the RE bout with mRNA expression determined by quantitative real-time polymerase chain reaction. No significant changes in the mRNA expression of either PGC-1α isoform were observed after acute eccentric RE (p > 0.05). IGF-1Ea mRNA expression significantly increased (p ≤ 0.05), whereas IGF-1Eb and mechano-growth factor (MGF) did not significantly change (p > 0.05). PGC-1α4 mRNA expression was associated with reduced mRNA expression of the catabolic gene myostatin (R = -0.88, p < 0.01), whereas MGF mRNA expression was associated with reduced mRNA expression of the catabolic gene FOXO3A (R = -0.81, p ≤ 0.05). These data demonstrate an attenuated response of PGC-1α isoforms to an acute bout of maximal eccentric exercise with short rest periods in postmenopausal women.

Associated decrements in rate of force development and neural drive after maximal eccentric exercise.

The present study investigated the changes in contractile rate of force development (RFD) and the neural drive following a single bout of eccentric exercise. Twenty-four subjects performed 15 × 10 maximal isokinetic eccentric knee extensor contractions. Prior to and at 24, 48, 72, 96, and 168 h during post-exercise recovery, isometric RFD (30, 50 100, and 200 ms), normalized RFD [1/6,1/2, and 2/3 of maximal voluntary contraction (MVC)] and rate of electromyography rise (RER; 30, 50, and 75 ms) were measured. RFD decreased by 28-42% peaking at 48 h (P < 0.01-P < 0.001) and remained depressed at 168 h (P < 0.05). Normalized RFD at 2/3 of MVC decreased by 22-39% (P < 0.01), peaked at 72 h and returned to baseline at 168 h. These changes in RFD were associated with a decrease in RER at 48 h-96 h (P < 0.05-P < 0.001). Accumulated changes (area under curve) revealed a greater relative decrease in accumulated RFD at 100 ms by -2727 ± 309 (%h; P < 0.05) and 200 ms by -3035 ± 271 (%h; P < 0.001) compared with MVC, which decreased, by -1956 ± 234 (%h). In conclusion, RFD and RER are both markedly reduced following a bout of maximal eccentric exercise. This association suggests that exercise-induced decrements in RFD can, in part, be explained decrements in neural drive.

The effects of anatabine on non-invasive indicators of muscle damage: a randomized, double-blind, placebo-controlled, crossover study

BackgroundAnatabine (ANA), a minor tobacco alkaloid found in the Solanaceae family of plants, may exhibit anti-inflammatory activity, which may be useful to aid in recovery from exercise-induced muscle damage. The purpose of this study, therefore, was to examine the effects of ANA supplementation on the recovery of isometric strength and selected non-invasive indicators of muscle damage.MethodsA double-blinded, placebo-controlled, crossover design was used to study eighteen men (mean ± SD age = 22.2 ± 3.1 yrs; body mass = 80.3 ± 15.7 kg) who participated in two randomly-ordered conditions separated by a washout period. The ANA condition consisted of consuming 6–12 mg anatabine per day for 10 days, while testing took place during days 7–10. The placebo (PLA) condition was identical except that the PLA supplement contained no ANA. Maximal voluntary isometric peak torque (PT) of the forearm flexors, arm circumference, hanging joint angle, and subjective pain ratings were measured before (PRE), immediately after (POST), and 24, 48, and 72 h after six sets of 10 maximal, eccentric isokinetic forearm flexion muscle actions. Resting heart rate and blood pressure were measured at PRE and 72 h in each condition.ResultsFor PT, hanging joint angle, arm circumference, and subjective pain ratings, there were no condition x time (p > 0.05) interactions, there were no main effects for condition (p > 0.05), but there were main effects for time (p < 0.001). There were no condition x time (p > 0.05) interactions and no main effects for condition (p > 0.05) or time (p > 0.05) for blood pressure or resting heart rate.ConclusionsANA supplementation had no effect on the recovery of muscle strength, hanging joint angle, arm swelling, or subjective pain ratings after a bout of maximal eccentric exercise in the forearm flexors. Therefore, ANA may not be beneficial for those seeking to improve recovery from heavy eccentric exercise. Future studies should examine the effects of ANA on the pro-inflammatory cytokine responses to exercise-induced muscle damage and the chronic low-grade inflammation observed in obese and elderly individuals.

Rate Of Velocity Development Less Decreased Following The Repeated Bout Of Maximal Eccentric Exercise

It has been reported that rate of velocity development (RVD) and strength are two of important measures of athletic performance, and eccentric exercise-induced muscle damage can be impaired RVD and strength performance (Nguyen et al., 2009 JSRC). It is well-documented that a bout of eccentric exercise confers protection against muscle damage after a subsequent bout of the same exercise performed several weeks to several months later (Clarkson et al., 1992 MSSE), but no study has examined effect of repeated bout of eccentric exercise on changes in RVD. PURPOSE: This study was to test the hypothesis that a repeated bout of maximal eccentric exercise of the elbow flexors would be less decreased RVD and faster recovery in comparison with the first bout. METHODS: Ten untrained young men (21.0 ± 3 yrs) performed 2 bouts of 30 maximal eccentric exercises (MAX1 & MAX2; 30°/s) of the elbow flexors of the non-dominant arm separated by 2 weeks. Maximal isokinetic concentric strength (MVC) and RVD (300°/s), muscle soreness, and range of motion were measured before, immediately after, and for 5 consecutive days after each bout. All data was analyzed by a two-way repeated measures ANOVA. RESULTS: The first bout of maximal eccentric exercise produced significant (P<0.05) decrease in maximal concentric strength (39%), RVD (49%), range of motion, and increase in muscle soreness. The changes in all criterion measures (e.g. MVC: 30%, RVD: 44%) after the second bout of the same exercise were significantly smaller (P<0.05) than that of the first bout. CONCLUSION: These results supported that MAX1 induced significantly muscle damage and soreness would be affected RVD, and protective effect occurred following the first bout of eccentric exercise results in a smaller decrease in RVD and faster recovery when the exercise is repeated after 2 weeks.

Potent Protective Effect Conferred by Four Bouts of Low-Intensity Eccentric Exercise

It is known that submaximal eccentric exercise does not confer as strong a protective effect as maximal eccentric exercise. This study tested the hypothesis that four bouts of submaximal eccentric exercise would confer a similar protective effect to one bout maximal eccentric exercise. Thirty untrained men were placed into 4 x 40% (40%) or control (CON) groups (n = 15 per group) by matching preexercise maximal voluntary isometric contraction strength (MVC). The 40% group performed 30 eccentric contractions with a load of 40% MVC (40% ECC) every 2 wk for four times followed 2 wk later by 30 maximal eccentric exercise (100% ECC) of the elbow flexors of the nondominant arm. The CON group performed two bouts of the 100% ECC separated by 2 wk. MVC at six angles, optimum angle (OA), concentric isokinetic strength (30 degrees x s(-1) and 300 degrees x s(-1)), range of motion, upper arm circumference, plasma creatine kinase activity and myoglobin concentration, muscle soreness, and echo intensity of B-mode ultrasound images were taken before to 5 d after each exercise. No significant differences in the changes in any measures were evident between the 100% ECC of the 40% group and the second 100% ECC of the CON group. Changes in all measures except for OA and upper arm circumference after the second to the fourth 40% ECC bouts were significantly smaller than those after the first 40% ECC bout. The changes in the measures after any of the 40% ECC bouts were significantly (P < 0.05) smaller than those after the first 100% ECC bout of the CON group. These results suggest that repeating submaximal eccentric exercise confers the same magnitude of protective effect as one bout of maximal eccentric exercise against the subsequent maximal eccentric exercise.

Hormone Replacement Therapy and Messenger RNA Expression of Estrogen Receptor Coregulators after Exercise in Postmenopausal Women

The use of hormone replacement therapy (HRT) is a potential treatment to relieve symptoms of menopause in postmenopausal women; however, the effects on skeletal muscle are unclear. Specifically, it is unknown if HRT enhances estrogen receptor (ER) transcriptional activation in skeletal muscle at rest and after resistance exercise. To evaluate changes in the messenger RNA (mRNA) expression of ER coregulators (steroid receptor coactivator-1 (SRC-1) and silencing mediator of retinoid and thyroid receptors (SMRT)) in postmenopausal women after a maximal eccentric exercise bout. Fourteen postmenopausal women were divided into two groups: control, women not using HRT (n = 6, 59.2 +/- 4.2 yr, 63.1 +/- 17.4 kg); or HRT, women using traditional HRT (n = 8, 58.5 +/- 3.7 yr, 89.5 +/- 23.7 kg). Participants performed 10 sets of 10 maximal eccentric repetitions of single-leg extension on the Cybex dynamometer at 60 degrees .s with 20-s rest periods between sets. Muscle biopsies of the vastus lateralis were obtained from the exercised leg at baseline and 4 h after the exercise bout. mRNA expression was determined using real-time polymerase chain reaction for SRC-1 and SMRT. mRNA expression of SRC-1 significantly increased (P < or = 0.01; 2.4- to 5.2-fold change) and mRNA expression of SMRT significantly decreased (P < or = 0.01; -1.3- to -4.3-fold change) after the exercise bout in both groups. We observed significantly greater changes in mRNA expression of SRC-1 and SMRT (P < or = 0.01) in the HRT group compared with controls after exercise. A single bout of maximal eccentric exercise enhances ER transcriptional activity with a greater response present in postmenopausal women using HRT.

Influence Of Hormone Replacement Therapy With Maximal Eccentric Exercise On Estrogen Receptor Coregulators And Skeletal Muscle Damage In Postmenopausal Women

The use of hormone replacement therapy (HRT) is a potential treatment to relieve symptoms of menopause and prevent the onset of disease such as osteoporosis in postmenopausal women. Although estrogen has a possible protective effect against exercise-induced skeletal muscle damage, it is unclear if HRT therapy enhances estrogen receptor (ER) activity in skeletal muscle at rest and following resistance exercise. PURPOSE: To evaluate changes in the mRNA gene expression of ER coregulators (SRC and SMRT) and markers of skeletal muscle damage (CK, LDH, and TNF-a) in postmenopausal women following a high-intensity resistance exercise bout. METHODS: Fourteen postmenopausal women were divided into two groups: Control, women not using HRT (n=6, 59±2 yr, 63±7 kg), or HRT, women using traditional HRT (n=8, 59±1 yr, 89.5±8.4 kg). Both groups performed 10 sets of 10 maximal eccentric repetitions of single-leg extension on the Cybex dynamometer at 60°/s with 20 second rest periods between sets. Two muscle biopsies of the vastus lateralis were obtained from the exercised leg at baseline and 4 hours after the exercise bout. mRNA gene expression was determined using RT-PCR for SRC, SMRT, and TNF-a. Blood draws were performed at baseline and 3 days post-exercise to measure CK and LDH. Independent t-tests were performed to test group differences (Control vs HRT). A probability level of p≤0.05 was used to determine statistical significance with Bonferroni adjustments. RESULTS: We observed significantly greater changes in mRNA expression of SRC and SMRT (p≤0.01) and significantly lower changes in mRNA expression of TNF-a (p≤0.01) in the HRT group compared to controls following the exercise bout. mRNA expression of SRC significantly increased (p≤0.01) and mRNA expression of SMRT significantly decreased (p≤0.01) following the exercise bout in both groups. CK and LDH levels were significantly greater post-exercise (p≤0.01) in the Control group. CONCLUSIONS: These data suggest a single bout of maximal eccentric exercise significantly enhances ER activity with greater response present in postmenopausal women using HRT. Postmenopausal women not using HRT experienced greater muscle damage after exercise indicating a possible protective effect of HRT against exercise-induced skeletal muscle damage. Keywords: SRC, SMRT, muscle damage

Muscle Function in Men and Women During Maximal Eccentric Exercise

This study assessed muscle fatigue patterns of the elbow flexors in untrained men and women to determine if sex differences exist during acute maximal eccentric exercise. High-intensity eccentric exercise is often used by athletes to elicit gains in muscle strength and size gains. Development of fatigue during this type of exercise can increase risk of injury; therefore, it is important to understand fatigue patterns during eccentric exercise to minimize injury risk exposure while still promoting training effects. While many isometric exercise studies have demonstrated that women show less fatigue, the patterns of fatigue during purely eccentric exercise have not been assessed in men and women. Based on the lack of sex differences in overall strength loss immediately post-eccentric exercise, it was hypothesized that women and men would have similar relative fatigue pattern responses (i.e., change from baseline) during a single bout of maximal eccentric exercise. Forty-six subjects (24 women and 22 men) completed 5 sets of 10 maximal eccentric contractions on an isokinetic dynamometer. Maximal voluntary isometric contraction strength was assessed at baseline and immediately following each exercise set. Maximal eccentric torque and contractile properties (i.e., contraction time, work, half relaxation time, and maximal rate of torque development) were calculated for each contraction. Men and women demonstrated similar relative isometric (32% for men and 39% for women) and eccentric (32% for men and 39% for women) fatigue as well as similar deficits in work done and rates of torque development and relaxation during exercise (p > 0.05). Untrained men and women displayed similar relative responses in all measures of muscle function during a single bout of maximal eccentric exercise of the elbow flexors. Thus, there is no reason to suspect that women may be more vulnerable to fatigue-related injury.

The influence of eccentric exercise on mRNA expression of skeletal muscle regulators

To evaluate change in myostatin, follistatin, MyoD and SGT mRNA gene expression using eccentric exercise to study mechanisms of skeletal muscle hypertrophy. Young (28+/-5 years) and older (68+/-6 years) men participated in a bout of maximal single-leg eccentric knee extension on an isokinetic dynamometer at 60 degrees /s: six sets, 12-16 maximal eccentric repetitions. Muscle biopsies of the vastus lateralis were obtained from the dominant leg before exercise and 24 h after exercise. Paired t tests were used to compare change (pre versus post-exercise) for normalized gene expression in all variables. Independent t tests were performed to test group differences (young vs. older). A probability level of P<or=0.05 was used to determine statistical significance with Bonferroni adjustments. We observed no significant change in myostatin (-0.59+/-2.1 arbitrary units (AU); P=0.42), follistatin (0.22+/-3.4; P=0.85), MyoD (0.23+/-3.1; P=0.82), or SGT (1.2+/-6.4; P=0.58) mRNA expression in young subjects 24 h after eccentric exercise. Similarly, we did not observe significant change in myostatin (-3.83+/-8.8; P=0.23), follistatin (-2.66+/-5.2; P=0.17), MyoD (-0.13+/-3.1; P=0.90), or SGT (-1.6+/-3.5; P=0.19) mRNA expression in older subjects. Furthermore, the non-significant changes in mRNA expression were not different between young and older subjects, P>0.23 for all variables. Our data suggests that a single bout of maximal eccentric exercise does not alter myostatin, follistatin, MyoD or SGT mRNA gene expression in young or older subjects.

Evidence of a contralateral repeated bout effect after maximal eccentric contractions

The aim of this investigation was firstly, to examine whether a contralateral repeated bout effect is manifested after a single bout of maximal eccentric muscle actions and secondly, to compare the magnitude of any such protection to an ipsilateral control. Sixteen male subjects undertook 45 repetitions of maximal eccentric contractions of the elbow flexors. The ipsilateral group (IL, N=8) repeated the exercise using the same arm and the contralateral group (CL, N=8) repeated the exercise using the contralateral arm 14 days later. Serum creatine kinase (CK), muscle soreness, maximal voluntary contraction (MVC) and range of motion (ROM) were significantly attenuated in the repeated bout for IL. CL also showed a significant reduction in the repeated bout for CK, muscle soreness and MVC. Despite the significant attenuation of dependent variables in both groups the magnitude of change was less in CL compared to IL for CK, soreness, MVC and ROM. The findings demonstrate a repeated bout effect in the contralateral limb after a single bout of maximal eccentric exercise; however, the magnitude of protection in the contralateral limb is less than that manifested in the ipsilateral limb. The apparent contralateral repeated bout effect observed in this investigation is thought to be predominantly mediated by neural mechanisms, although further research is required to elucidate this possibility.

Repeated Bout Effect after Maximal Eccentric Exercise

We hypothesized that a bout of high or low volume eccentric exercise would protect against muscle damage following a subsequent high volume bout and that adaptation would be attributable to neural changes, independent of the initial exercise volume. Sixteen males performed either 45 (ECC45) or 10 (ECC10) maximal eccentric contractions using the elbow flexors, followed by an ECC45 bout 2 weeks later. Damage markers were measured for the following 96 h; EMG and work done during the first 10 eccentric contractions were also recorded. CK, soreness, and decrements in MVC and range of motion (ROM) were greater in bout 1 than bout 2 (p < 0.01). Soreness, MVC and ROM were greater after the initial ECC45 bout compared to the initial ECC10 bout and the repeated bouts of ECC45 exercise in both groups (p < 0.01). Median frequency decreased from bout 1 to bout 2 (p < 0.001), no differences between groups were observed. An ECC45 bout of maximal eccentric exercise causes more initial damage than an ECC10 bout of maximal eccentric exercise, although both confer protection from subsequent ECC45 bouts of maximal eccentric contractions, which are attributable, at least in part, to a shift in the frequency content of EMG.

Satellite cell numbers in young and older men 24 hours after eccentric exercise

We tested the hypothesis that the expansion of satellite cell numbers, 24 h after maximal eccentric knee extensor exercise, is blunted in older men. Muscle biopsies were obtained from the vastus lateralis of 10 young (23-35 years) and 9 older (60-75 years) men. Satellite cells were identified immunohistochemically using an antibody to neural cell adhesion molecule. After 92 maximal eccentric contractions, the mean number of satellite cells per muscle fiber increased to a greater extent among the young men (141%; P < 0.001) than older men (51%; P = 0.002) from preexercise levels. Similar results were obtained when satellite cells were expressed as a proportion of all sublaminar nuclei. We conclude that a single bout of maximal eccentric exercise increases satellite cell numbers in both age groups, with a significantly greater response among the young men. These data suggest that age-related changes in satellite cell recruitment may contribute to muscle regeneration deficits among the elderly.

The Repeat Bout Effect Following Initial Low and High Volume Eccentric Exercise

2195 An initial bout of eccentrically biased exercise protects skeletal muscle against damage in subsequent bouts, but the volume required to elicit protection is unclear. One mechanism that could mediate this protective effect is a shift in motor unit recruitment in the repeat bout, towards motor units that were used to a lesser extent or not at all in the initial bout. PURPOSE: To compare markers of muscle damage and surface electromyography (EMG) activity from an initial low volume (LV) or high volume (HV) bout followed by a subsequent HV bout of maximal eccentric exercise. METHODS: Sixteen males were assigned to a LV or HV group (10 and 45 maximal eccentric contractions of the elbow flexors, respectively). Surface EMG activity was recorded during the first 10 contractions of each bout from the biceps brachii. The damage markers of creatine kinase (CK), soreness rating (DOMS) and maximum isometric strength (MVC) were measured before, 48 h and 96 h after the initial exercise and at the same time periods before and following a subsequent bout of HV eccentric exercise performed 14 days later. RESULTS: DOMS (F = 19.3) and MVC (F = 11.7) showed significant (p<0.01) group × bout interactions; both DOMS (69.5%) and MVC (13.2%) were attenuated (p<0.01) in bout 2 for the HV group, however there were no differences between groups in bout 2. Median frequency (MDF) significantly decreased from the initial bout to the subsequent bout by 9.7% (F = 9.4, p<0.01), without differences between groups. Eccentric torque in the first 10 contractions increased non-significantly between bouts (8.8%). CONCLUSIONS: Both LV and HV maximal eccentric exercise produce a repeat bout effect in subsequent HV bouts. It would appear that any changes eliciting a repeat bout effect may be attributed, at least in part, to a neural adaptation in the first 10 maximal eccentric contractions of the initial exercise bout. The reduction in MDF may indicate a shift in motor unit recruitment that is independent of the volume of the initial exercise bout.

The Repeat Bout Effect Following Initial Low and High Volume Eccentric Exercise

2195 An initial bout of eccentrically biased exercise protects skeletal muscle against damage in subsequent bouts, but the volume required to elicit protection is unclear. One mechanism that could mediate this protective effect is a shift in motor unit recruitment in the repeat bout, towards motor units that were used to a lesser extent or not at all in the initial bout. PURPOSE: To compare markers of muscle damage and surface electromyography (EMG) activity from an initial low volume (LV) or high volume (HV) bout followed by a subsequent HV bout of maximal eccentric exercise. METHODS: Sixteen males were assigned to a LV or HV group (10 and 45 maximal eccentric contractions of the elbow flexors, respectively). Surface EMG activity was recorded during the first 10 contractions of each bout from the biceps brachii. The damage markers of creatine kinase (CK), soreness rating (DOMS) and maximum isometric strength (MVC) were measured before, 48 h and 96 h after the initial exercise and at the same time periods before and following a subsequent bout of HV eccentric exercise performed 14 days later. RESULTS: DOMS (F = 19.3) and MVC (F = 11.7) showed significant (p<0.01) group × bout interactions; both DOMS (69.5%) and MVC (13.2%) were attenuated (p<0.01) in bout 2 for the HV group, however there were no differences between groups in bout 2. Median frequency (MDF) significantly decreased from the initial bout to the subsequent bout by 9.7% (F = 9.4, p<0.01), without differences between groups. Eccentric torque in the first 10 contractions increased non-significantly between bouts (8.8%). CONCLUSIONS: Both LV and HV maximal eccentric exercise produce a repeat bout effect in subsequent HV bouts. It would appear that any changes eliciting a repeat bout effect may be attributed, at least in part, to a neural adaptation in the first 10 maximal eccentric contractions of the initial exercise bout. The reduction in MDF may indicate a shift in motor unit recruitment that is independent of the volume of the initial exercise bout.

THE EFFECTS OF A SUBSEQUENT BOUT OF MAXIMAL ECCENTRIC CONTRACTIONS ON EMG RESPONSE

PURPOSE This study investigated whether a subsequent bout of maximal eccentric exercise repeated 3 days following the first exercise bout would result in changes in electromyographic (EMG) response. METHODS Twenty-six (26) male students (20.7; ¡Ó 2.5 yrs) were randomly assigned to experimental 70 repetitions (EX70; n=9), experimental 30 repetitions (EX30;n=8), and control (CON; n=9) groups. The first exercise was 30 maximal voluntary isokinetic eccentric contractions (MAX1) on non-dominant elbow flexors at 60¢X/s. The EX70 and EX30 groups repeated a second bout of 70 and 30 eccentric actions (MAX2), respectively, three days after MAX1. Total work, work per contraction, IEMG and MPF were recorded during MAX1 and MAX2. RESULTS Total work, IEMG, and MPF were lower for MAX2 compared to MAX1 for both the EX30 and EX70 subjects (p < 0.05). These EMG findings were consistent with reduced activation of fast-twitch motor units during the second eccentric bout. CONCLUSION Repeating a subsequent bout of eccentric exercise three days after the first bout lowered the EMG response, even when the subsequent bout of exercise was more strenuous. These results may be suggested as evidence of a neural protective mechanism.

Is recovery from muscle damage retarded by a subsequent bout of eccentric exercise inducing larger decreases in force?

The aim of this study was to investigate whether a subsequent bout of eccentric exercise inducing larger decreases in force than the initial bout would exacerbate muscle damage and retard recovery. Changes in indirect markers of muscle damage were measured over 14 days when 24 maximal eccentric actions of the elbow flexors were performed on days 1 (ECC1) and 7 (ECC2], with electrical stimulation superimposed percutaneously to the elbow flexors during maximal eccentric actions in ECC2. Maximal isometric force (MIF), range of motion (ROM), upper arm circumference, muscle soreness, B-mode ultrasound, and several muscle proteins in the blood were assessed before, immediately after and for 5 days after both bouts. Magnetic resonance Imaging (MRI) was assessed 4 days after both bouts. MIF decreased to 45% of the pre-exercise value immediately after ECC 1 and recovered to 59% by day 7 post-exercise. MIF decreased to 22% of pre-ECC1 value immediately after ECC2, but recovered to 105% of pre-ECC2 value 5 days following ECC2. Recovery of MIF and ROM was slightly retarded for 1-2 days after ECC2. However circumference, muscle soreness, and biochemical parameters did not increase following ECC2. There were no signs of additional damage in ultrasound and MRI after ECC2. It was concluded that a second bout of maximal eccentric exercise with electrical stimulation slightly retarded recovery of muscle function with minimal muscle damage.