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.     

The effects of a repeated bout of eccentric exercise on indices of muscle damage and delayed onset muscle soreness

This study examined markers of muscle damage following a repeated bout of maximal isokinetic eccentric exercise performed prior to full recovery from a previous bout. Twenty non-resistance trained volunteers were randomly assigned to a control (CON, n=10) or experimental (EXP, n=10) group. Both groups performed 36 maximal isokinetic eccentric contractions of the elbow flexors of the non-dominant arm (ECC1). The EXP group repeated the same eccentric exercise bout two days later (ECC2). Total work and peak eccentric torque were recorded during each set of ECC1 and ECC2. Isometric torque, delayed onset muscle soreness (DOMS), flexed elbow angle and plasma creatine kinase (CK) activity were measured prior to and immediately following ECC1 and ECC2. at 24h intervals for 7 days following ECC1 and finally on day 11. In both groups, all dependent variables changed significantly during the 2 days following ECC1. A further acute post-exercise impairment in isometric torque (30 +/- 5%) and flexed elbow angle (20 +/- 4%) was observed following ECC2 (p<0.05), despite EXP subjects producing uniformly lower work and peak eccentric torque values during ECC2 (p<0.05). No other significant differences between the CON and EXP groups were observed throughout the study (p>0.05). These findings suggest that when maximal isokinetic eccentric exercise is repeated two days after experiencing of contraction-induced muscle damage, the recovery time course is not significantly altered.     

Differential expression of muscle damage in humans following acute fast and slow velocity eccentric exercise

We sought to determine if the velocity of an acute bout of eccentric contractions influenced the duration and severity of several common indirect markers of muscle damage. Subjects performed 36 maximal fast (FST, n = 8: 3.14 rad x s(-1)) or slow (SLW, n = 7: 0.52 rad x s(-1)) velocity isokinetic eccentric contractions with the elbow flexors of the non-dominant arm. Muscle soreness, limb girth, plasma creatine kinase (CK) activity, isometric torque and concentric and eccentric torque at 0.52 and 3.14 rad x s(-1) were assessed prior to and for several days following the eccentric bout. Peak plasma CK activity was similar in SLW (4030 +/- 1029 U x 1(-1)) and FST (5864 +/- 2664 U x 1(-1)) groups, (p > 0.05). Both groups experienced similar decrement in all strength variables during the 48 hr following the eccentric bout. However, recovery occurred more rapidly in the FST group during eccentric (0.52 and 3.14 rad x s(-1)) and concentric (3.14 rad x s(-1)) post-testing. The severity of muscle soreness was similar in both groups. However, the FST group experienced peak muscle soreness 48 hr later than the SLW group (24 hr vs. 72 hr). The SLW group experienced a greater increase in upper arm girth than the FST group 20 min, 24 hr and 96 hr following the eccentric exercise bout. The contraction velocity of an acute bout of eccentric exercise differentially influences the magnitude and time course of several indirect markers of muscle damage.     

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.     

Effect of single bout versus repeated bouts of stretching on muscle recovery following eccentric exercise

ObjectivesTo analyze the effects of a single bout and repeated bouts of stretching on indirect markers of exercise-induced muscle damage.DesignA randomized controlled clinical trial at a university human research laboratory was conducted.MethodsFifty-six untrained males were randomly divided into four groups. (I) a single stretching group underwent a single bout of stretching on the quadriceps muscle; (II) an eccentric exercised group underwent eccentric quadriceps muscle contractions until exhaustion; (III) an eccentric exercise group followed by a single bout of stretching; (IV) an eccentric exercised group submitted to repeated bouts of stretching performed immediately and 24, 48, and 72 h post-exercise. Muscle stiffness, muscle soreness, maximal concentric peak torque, and plasma creatine kinase activity were assessed before exercise and 1, 24, 48, 72, and 96 h post-exercise.ResultsAll exercised groups showed significant reduction in maximal concentric peak torque and significant increases in muscle soreness, muscle stiffness, and plasma creatine kinase. There were no differences between these groups in all assessed variables, with the exception of markers of muscle stiffness, which were significantly lower in the eccentric exercise group followed by single or repeated bouts. The single stretching group showed no change in any assessed variables during the measurement period.ConclusionsMuscle stretching performed after exercise, either as single bout or as repeated bouts, does not influence the levels of the main markers of exercise-induced muscle damage; however, repeated bouts of stretching performed during the days following exercise may have favorable effects on muscle stiffness.     

A light load eccentric exercise confers protection against a subsequent bout of more demanding eccentric exercise

This study investigated the hypothesis that a light eccentric exercise (ECC) that does not induce a loss of muscle function and delayed onset muscle soreness would confer a protective effect against a more strenuous ECC. Eighteen young men were randomly placed into two groups: 10–40% (n = 9) and 40% (n = 9). Subjects in the 10–40% group performed ECC of the elbow flexors (six sets of five reps) using a dumbbell set at 10% of maximal isometric strength (MVC) at an elbow joint angle of 90°, followed 2 days later by ECC using a dumbbell weight of 40% MVC. Subjects in the 40% group performed the 40% ECC only. Changes in MVC, range of motion (ROM), upper arm circumference (CIR), plasma creatine kinase (CK) activity and muscle soreness before, immediately after, 1–5 and 7 days following the 40% ECC were compared between groups by a two-way repeated measures ANOVA. No significant changes in any of the criterion measures were found immediately and 1–2 days after the 10% ECC. Following the 40% ECC, the 10–40% group showed significantly (P < 0.05) smaller decreases in MVC and ROM, and smaller increases in muscle soreness compared with the 40% group, but no significant differences between groups were evident for CIR and plasma CK activity. These results suggest that the 10% ECC induced some protection against a subsequent bout of 40% ECC performed 2 days later. It appears that the light eccentric exercise preconditioned the muscles for exposure to the subsequent damaging eccentric exercise bout.     

Effects of number of eccentric muscle actions on first and second bouts of eccentric exercise of the elbow flexors

This study compared changes in indirect markers of muscle damage following eccentric exercise of the elbow flexors among the exercises consisting of different number of eccentric actions. Sixty male athletes were placed into one of the six groups (n=10 per group) based on the number of eccentric actions for the first (ECC1) and second exercise bouts (ECC2). Single bout groups (30, 50, and 70) performed ECC1 only, and repeated bout groups (30-30, 50-50, and 70-70) performed ECC2 3 days after ECC1. Another 10 male athletes performed different number of eccentric actions for ECC1 (30) and ECC2 (70) separated by 3 days (30-70). Changes in maximal isometric strength (MVC), range of motion (ROM), upper arm circumference (CIR), serum creatine kinase activity, myoglobin, and nitric oxide concentrations and muscle soreness for 10 days following ECC1 were compared among groups by two-way repeated measures ANOVA. Changes in MVC, ROM, and CIR following ECC1 were significantly (P<0.05) smaller for the groups that performed 30 eccentric actions compared with other groups. No significant differences between 30 and 30-30, 50 and 50-50, and 70 and 70-70 were evident for the changes in the measures for 10 days following ECC1 except for the acute decreases in MVC and ROM immediately after ECC2 for the repeated bout groups. The 30-30 and 30-70 groups showed similar changes in all criterion measures. It is concluded that recovery from eccentric exercise is not retarded by the second bout of eccentric exercise regardless of the number of eccentric actions.     

Decreased EMG median frequency during a second bout of eccentric contractions

PURPOSE: Others have reported preferential recruitment of fast motor units in muscles during performance of eccentric contractions and there is evidence that fast muscle fibers are more susceptible to eccentric contraction-induced injury. We tested the hypothesis that during a second bout of maximal eccentric contractions 1 wk after the first, there would be a reduction in the electromyographic (EMG) median frequency (MF) with minimal change in the EMG root-mean-square (RMS), indicating greater reliance on slower motor units. This could provide an explanation for the enhanced resistance to eccentric contraction-induced injury after a single bout of eccentric exercise. METHODS: Human subjects performed 50 maximal voluntary eccentric (N = 10) or concentric (N = 10) contractions of the anterior crural muscles on two occasions separated by 1 wk. To determine whether MF changes during the second bout could be a consequence of injury to fibers in fast motor units, the anterior crural muscles of mice were electrically stimulated to perform 50 maximal eccentric (N = 10) or concentric (N = 9) contractions on two occasions separated by 1 wk. In both the humans and mice, torque production and tibialis anterior muscle RMS and MF were measured during the two exercise bouts. RESULTS: In human tibialis anterior muscle, MF was 30% lower (P < 0.01) during the second eccentric bout although RMS was the same. In the mice, RMS and MF were unchanged at any time after the first eccentric bout despite torque deficits similar to those observed in the humans. CONCLUSIONS: The data indicate that with repetition of maximal voluntary eccentric contractions, there is an increased activation of slow motor units and a concomitant decrease in activation of fast units.     

Changes in markers of muscle damage of middle-aged and young men following eccentric exercise of the elbow flexors

It is well documented that unaccustomed eccentric exercise induces muscle damage, but the responses of middle-aged individuals to a bout of eccentric exercise have not been reported. The purpose of this study was to compare changes in indirect markers of muscle damage following eccentric exercise of the elbow flexors between 12 young (age: 19.4+/-0.4 years, height: 173.5+/-2.0cm, body mass: 65.8+/-3.5kg) and 12 middle-aged men (48.0+/-2.1 years, 169.5+/-1.7cm, 67.3+/-1.6kg). It was hypothesized that middle-aged men would be more susceptible to muscle damage than young men. All subjects performed six sets of five eccentric actions of the elbow flexors using a dumbbell of 40% of maximal isometric strength (MVC). Changes in MVC, elbow joint angles and range of motion, upper arm circumference, plasma creatine kinase activity and myoglobin concentration, and muscle soreness before, immediately after, and 1, 2, 3, and 4 days after exercise were compared between the young and middle-aged groups by a two-way repeated measures ANOVA. All criterion measures changed significantly (P<0.05) after exercise, but no significant differences in the changes in the measures except for muscle soreness were evident between groups. Development of muscle soreness after exercise was significantly (P<0.05) lower (approximately a half of the value) for the middle-aged group compared with the young group. These results did not support the hypothesis that middle-aged men would be more susceptible to muscle damage than young men.     

Effects of eccentric exercise on trunk extensor torque and lumbar paraspinal EMG

PURPOSE: Little is known about the effects of eccentric contractions on the function of the lumbar paraspinal muscles. The purpose of this study was to determine the effects of a single bout of eccentric contractions using the trunk extensor muscles on torque and lumbar paraspinal electromyographic (EMG) parameters. METHODS: Twenty healthy men between the ages of 18 and 49 yr participated in the study. Subjects performed a single bout of 50 maximal voluntary concentric (N = 10) or eccentric (N = 10) trunk extension movements while surface EMG signals were recorded from the multifidus and iliocostalis lumborum muscles. A series of isometric contractions were performed both before the exercise protocol and at five additional time points over the following 7 d. RESULTS: During the exercise protocol, peak torque decreased 30% and 24% in the eccentric and concentric groups, respectively, whereas no change occurred in EMG root-mean-square (RMS). There were no group differences in peak torque generation at any of the postexercise protocol time points. Compared with the preexercise protocol values, multifidus EMG was elevated 27% immediately post and 15 min post in the eccentric group. Similarly, compared with the concentric group, multifidus EMG in the eccentric group was increased 34%, 40%, and 25% immediately post, 15 min post, and 1 d after the exercise protocol, respectively. CONCLUSION: Eccentric contractions using the trunk extensor muscles result in higher levels of multifidus EMG activity to produce a given level of torque. This reduction in neuromuscular efficiency persisted for one day with recovery to baseline levels by the third day. Contrary to studies using other muscle groups, no sustained alteration in muscle function was observed.     

Greater muscle damage induced by fast versus slow velocity eccentric exercise

Debate exists concerning the effect of contraction velocity on muscle damage, and few human studies have yet to address this issue. This study examined whether the velocity of eccentric exercise affected the magnitude of muscle damage. Twelve untrained subjects performed a series of slow velocity isokinetic eccentric elbow flexions (SV: 30 degrees . s (-1)) of one arm and a fast velocity exercise (FV: 210 degrees . s (-1)) of the other arm, separated by 14 days. In order to standardise the time under tension (120 s) for the two conditions, the number of muscle actions for SV was 30 and 210 for FV. Criterion measures consisted of maximal voluntary torque for isometric, concentric (4 velocities) and eccentric contractions (2 velocities), range of motion (ROM) and relaxed elbow joint angle (RANG), upper arm circumference, muscle soreness and plasma creatine kinase (CK) activity. Measures were taken before, immediately after, 0.5 hour and 24 - 168 hours (240 hours for CK) after each eccentric exercise protocol, and changes in the measures over time were compared between FV and SV by two-way repeated measures ANOVA. Both protocols resulted in significant decrements in isometric and dynamic torque (p < 0.01), but FV showed significantly (p < 0.05) greater reductions over time ( approximately 55 %) and a slower recovery compared to SV ( approximately 30 %). Significantly (p < 0.05) larger decreases in, and delayed recovery of, ROM and RANG were evident after FV compared to SV. FV had significantly (p < 0.05) larger increases in upper arm circumference and soreness compared to SV, and peak plasma CK activity was 4.5-fold greater (p < 0.05) following FV than SV. These results suggest that, for the same time under tension, fast velocity eccentric exercise causes greater muscle damage than slow velocity exercise in untrained subjects.     

Delayed-onset muscle soreness does not reflect the magnitude of eccentric exercise-induced muscle damage

This study investigated the relationship between delayed-onset muscle soreness and other indicators of muscle damage following eccentric exercise. Male students (n = 110) performed 12 (12ECC), 24 (24ECC), or 60 maximal eccentric actions of the elbow flexors (60ECC). Maximal isometric force, relaxed and flexed elbow joint angles, upper arm circumference, and plasma creatine kinase activity were assessed immediately before and after, and for 4 days after exercise. Muscle soreness (SOR) was evaluated by a visual analog scale (a 50-mm line, 0: no pain, 50: extremely painful) when the elbow flexors were palpated (SOR-Pal), flexed (SOR-Flx) and stretched (SOR-Ext). Although 24ECC and 60ECC resulted in significantly (P <; 0.05) larger changes in all indicators and slower recovery compared to 12ECC, no significant differences were evident for SOR-Pal and SOR-Flx between 12ECC and 24ECC, or 12ECC and 60ECC. In contrast, SOR-Ext was significantly (P <; 0.05) lower for 12ECC compared to 24ECC and 60ECC. A Pearson product-moment correlation showed SOR-Pal did not correlate significantly with any indicators, however, SOR-Ext and SOR-Flx showed weak (r <; 0.32) but significant (P <; 0.05) correlations with other indicators. Because of generally poor correlations between DOMS and other indicators, we conclude that use of DOMS is a poor reflector of eccentric exercise-induced muscle damage and inflammation, and changes in indirect markers of muscle damage and inflammation are not necessarily accompanied with DOMS.     

Differential effects of exhaustive cycle ergometry on concentric and eccentric torque production

The purpose of this study was to investigate the potential differences in peak isokinetic concentric end eccentric torque following low- and high-intensity cycle exercise fatigue protocols. Ten healthy, recreationally-active men were tested in a balanced, randomized testing sequence for peak eccentric and concentric isokinetic torque (60 degrees/sec) immediately before and after three experimental conditions each separated by 48 hours: 1) a bout of high intensity cycling consisting of a maximal 90-second sprint; 2) a bout of low-intensity cycling at 60 rpm equated for total work with the high-intensity protocol: and 3) no exercise (control bout). Blood was drawn from an antecubital vein and plasma lactate concentrations were determined immediately before and after each experimental bout. Post-exercise plasma lactate concentrations were 15.1 +/- 2.5 and 4.7 +/- 1.9 mmol l(-1), respectively, following the high- and low-intensity protocols. The high intensity exercise bout resulted in the only post-exercise decrease in concentric and eccentric isokinetic peak torque. The percent decline in maximal force production was significantly (P< 0.05) greater for concentric muscle actions compared to eccentric (29 vs 15%, respectively). In conclusion, a 90-second maximal cycling sprint results in a significant decline in maximal torque of both concentric and eccentric muscle actions with the greatest magnitude observed during concentric muscle actions.     

Muscle function at the wrist after eccentric exercise

PURPOSE: The purpose of this experiment was to investigate the effects of eccentric exercise by the wrist extensor muscles on the function and motor control of synergist wrist extensor muscles and the antagonist wrist flexor muscles. METHODS: Ten subjects were tested repeatedly over a period of 11 d, once before and four times after a bout of strenuous eccentric exercise with the wrist extensor muscles. Tests performed as indicators of muscle injury were wrist extension MVC, ROM, and soreness. Tests performed as measures of function and motor control were maximum joint velocity, ability to sustain a constant torque, and the ability to track a changing torque. RESULTS: Indicators of muscle injury: subjects exhibited a decline in wrist extension MVC and ROM, which peaked on day 1, and reported that muscle soreness was greatest on day 2. All measures returned to baseline values by day 10. Measures of function and motor control: subjects exhibited a greater difficulty sustaining a submaximal contraction and tracking torque after eccentric exercise. Greater torque variances in these tests were most evident at high torque levels. Subjects exhibited the greatest difficulty 24 h after eccentric exercise and had recovered by day 10. There was no change in maximal wrist extension velocity. CONCLUSIONS: Strenuous eccentric exercise by wrist extensors had an effect on function and motor control of the wrist extensor muscles. The effect was most evident during contractions in which high torque was required. The response of all of the wrist extensors after the exercise bout was similar, suggesting that they operated in a synergistic manner. The antagonists wrist flexors showed increased coactivation after eccentric exercise.     

Early alterations in serum creatine kinase and total cholesterol following high intensity eccentric muscle actions

AIM: The purpose of this experiment was to assess the levels of muscle soreness, serum total cholesterol (TC) and creatine kinase (CK) in the first 48 hours following fatiguing eccentric exercise performed with the triceps brachii. METHODS: Eleven untrained male college students performed a total of 50 eccentric elbow extensions in 8 sets (6 x 7 and 2 x 4) with a load equal to 85% of their maximal concentric elbow extension strength. Isometric elbow extension strength, muscle soreness and circumference, and serum CK and TC concentrations were measured before, immediately after, and 2, 24 and 48 hours after the exercise. RESULTS: Statistically reliable changes in isometric strength, serum CK and TC, muscle soreness and upper arm circumference occurred within the first 48 hours following eccentric exercise. Serum TC concentrations exhibited a very rapid (within 2 hours) reduction from pre-exercise values after eccentric exercise to a relatively stable concentration of approximately 85% of baseline. CONCLUSION: These results suggest that serum TC concentration may follow the time-course of reductions in force generating capacity more closely than other biochemical markers of muscle damage.     

Acute alcohol consumption aggravates the decline in muscle performance following strenuous eccentric exercise

This study investigated the effects of acute moderate alcohol intake on muscular performance during recovery from eccentric exercise-induced muscle damage. Eleven healthy males performed 300 maximal eccentric contractions of the quadriceps muscles of one leg on an isokinetic dynamometer. They then consumed a beverage containing 1 g/kg bodyweight ethanol (as vodka and orange juice) (ALC). On another occasion they performed an equivalent bout of eccentric exercise on the contralateral leg after which they consumed an isocaloric quantity of orange juice (OJ). Measurement of maximal isokinetic (concentric and eccentric) and isometric torque produced across the knee, plasma creatine kinase (CK) concentrations and muscle soreness were made before and at 36 and 60 h following each exercise bout. All measures of muscle performance were significantly reduced at 36 and 60 h post-exercise compared to pre-exercise measures (all p < 0.05). The greatest decreases in peak strength were observed at 36 h with losses of 12%, 28% and 19% occurring for OJ isometric, concentric, and eccentric contractions, respectively. However, peak strength loss was significantly greater in ALC with the same performance measures decreasing by 34%, 40% and 34%, respectively. Post-exercise plasma creatine kinase activity and ratings of muscle soreness were not different between conditions (both p > 0.05). These results indicate that consumption of even moderate amounts of alcohol following eccentric-based exercise magnifies the normally observed losses in dynamic and static strength. Therefore, to minimise exercise related losses in muscle function and expedite recovery, participants in sports involving eccentric muscle work should avoid alcohol-containing beverages in the post-event period.     

Partial protection against muscle damage by eccentric actions at short muscle lengths

PURPOSE: This study investigated the hypothesis that maximal eccentric actions at a short muscle length would fail to confer a protective effect against muscle damage induced by maximal eccentric exercise at a long muscle length. METHODS: Eleven males performed 24 maximal eccentric actions of the nondominant elbow flexors over a short extension range from an elbow joint angle of 0.87-1.74 rad (S-ECC) followed 4 wk later by eccentric actions at a long range of 2.27-3.14 rad (L-ECC). A second group of 11 males performed L-ECC on two occasions using the nondominant arm separated by 4 wk. Changes in maximal isometric strength, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase and aspartate aminotransferase activities, and B-mode ultrasound images were compared between bouts and between groups by two-way repeated measures ANOVA. RESULTS: All measures changed significantly (P < 0.01) after the first bout; however, the effects were significantly (P < 0.01) smaller after S-ECC compared with L-ECC. The second bout resulted in significantly (P < 0.01) reduced changes in all measures compared with the first bout in the subjects who performed L-ECC on both occasions. The subjects who performed S-ECC in the first bout displayed significantly smaller changes after L-ECC than those seen after L-ECC alone, with the degree of attenuation being around 50-70%. CONCLUSION: Contrary to the hypothesis, S-ECC provided partial but effective protection against L-ECC. This result suggests adaptations associated with the repeated bout effect were also produced after S-ECC, but the degree of adaptations was not as strong as that by L-ECC. Eccentric exercise at a short extension range can be used as a strategy to present severe muscle damage.     

Do dominant and non-dominant arms respond similarly to maximal eccentric exercise of the elbow flexors?

ObjectivesTwo common models to investigate the effect of interventions on muscle damage include using two groups in which one group receives an intervention while the other acts as control, and using contralateral limbs of one group. The latter model is based on the assumption that changes in markers of muscle damage are similar between limbs, but this has not been examined systematically.DesignThis study compared changes in muscle damage markers between dominant and non-dominant arms following maximal eccentric exercise of the elbow flexors.MethodsEighteen men performed 60 maximal eccentric elbow flexions of each arm separated by 4 weeks with the order of testing between arms randomised. Maximal voluntary isometric torque, range of motion, upper arm circumference, plasma creatine kinase (CK) activity and muscle soreness before and for 7 days following exercise were compared between arms using two-way repeated measures ANOVA.ResultsNo significant differences between arms were evident for any of the markers, but significant (P < 0.05) differences between first and second bouts were evident for changes in strength, circumference and CK with smaller changes following the second bout. A poor correlation was found for the magnitude of changes in the markers between dominant and non-dominant arms, suggesting that responses to eccentric exercise were not necessarily the same between arms.ConclusionsThese results show that the order affected the responses of dominant and non-dominant arms to the eccentric exercise; however, the contralateral limb design appears to be usable if bout order is counterbalanced and randomised among participants.     

Effects of muscle damage induced by eccentric exercise on muscle fatigue

PURPOSE: The present study was designed to determine to what extent muscle damage induced by repetitive eccentric exercise with maximal voluntary effort (ECC) affects the time course of central and peripheral fatigue during sustained maximal voluntary contraction (MVC). METHODS: Ten healthy male volunteers were asked to perform brief (control MVC) and sustained MVC (fatigue test of 60 s in duration) with elbow flexion before and 2 and 4 d after ECC. Transcranial magnetic stimulation (TMS) was applied to the motor cortex to determine changes in voluntary activation (VA), the size of the motor evoked potential (MEP), and length of electromyographic (EMG) silencing. The ratio of the root mean square value for the surface EMG of the biceps brachii and exerted force within 50 ms before TMS was also calculated (RMS/F). RESULTS: In two subjects, no significant changes in MVC and muscle soreness were seen after ECC so that their data was excluded from further analysis. Control MVC and muscle soreness was significantly decreased and increased, respectively, 2 and 4 d after ECC compared with that before ECC (P < 0.001). During the fatigue test, VA, which was determined by a phasic increase in the twitch force after TMS, significantly decreased 2 and 4 d after ECC compared with that beforehand (P < 0.01). In addition, the RMS/F was significantly increased 2 and 4 d after ECC (P < 0.001). Although the degree of facilitation of the MEP was significantly increased (P < 0.05), the length of EMG silencing was less affected by ECC. CONCLUSIONS: Muscle damage and/or muscle soreness induced by repetitive eccentric exercise with maximal effort may be a strong modifier of central and peripheral fatigue during sustained MVC.     

Human hamstring muscles adapt to eccentric exercise by changing optimum length

PURPOSE: It is now established that unaccustomed eccentric exercise leads to muscle fiber damage and to delayed-onset muscle soreness (DOMS) in the days after exercise. However, a second bout of eccentric exercise, a week after the first, produces much less damage and soreness. The purpose of this study was to provide evidence from muscle mechanical properties of a proposed mechanism for this training effect in human hamstring muscles. METHODS: The eccentric exercise involved 12 sets of 6 repetition "hamstring lowers," performed on specially designed equipment. Hamstring angle-torque curves were constructed for each of 10 subjects (8 male and 2 female) while they performed maximum voluntary knee extension and flexion movements on an isokinetic dynamometer. Testing sessions were performed over the week before eccentric exercise, immediately post exercise, and daily, up to 8 d post exercise. Subject soreness ratings and leg girth measurements were also made post exercise. Six subjects performed a second bout of eccentric exercise, 8 d after the first, and measurements were continued up to 10 d beyond that. RESULTS: There was a significant shift in the optimum angle for torque generation (Lo), to longer muscle lengths immediately post exercise (7.7 degrees +/- 2.1 degrees, P < 0.01), indicating an increase in series compliance within some muscle fibers. Subsequent measurements showed increases in leg girth and some muscle soreness, suggesting muscle damage. The shift in Lo persisted, even after other injury parameters had returned to normal, consistent with a training effect. Subjects also showed fewer signs of muscle damage after the second exercise bout. CONCLUSION: This is the first study to show a sustained shift in optimum angle of human muscle as a protective strategy against injury from eccentric exercise. Implications of this work for athletes, particularly those prone to hamstring strains are discussed.