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.     

Acute adaptation to low volume eccentric exercise.

PURPOSE: Many symptoms of eccentric muscle damage can be substantially reduced if a similar eccentric bout is repeated within several weeks of the initial bout. The purpose of this study was to determine whether a nondamaging, low repetition, low volume eccentric exercise bout could also provide a protective/adaptive effect. METHODS: Subjects were assigned to a control (CON), eccentric exercise (ECC), or low volume familiarized eccentric exercise group (LV+ECC). Before the study, the LV+ECC group performed six maximal eccentric contractions during two familiarization sessions. The main eccentric bout targeted the elbow flexor muscle group and consisted of 36 maximal eccentric contractions. Muscle soreness, upper arm girth, elbow angle, creatine kinase activity, isometric torque, and concentric and eccentric torque at 0.52 and 3.14 rad.s-1 were assessed 0, 1, 2, 3, 4, 7, and 10 d postexercise. RESULTS: No evidence of muscle damage was observed as a result of the low volume eccentric bouts. Nevertheless, with the exception of muscle soreness and concentric torque, all variables recovered more rapidly in the LV+ECC group (P < 0.05). CONCLUSION: Adaptation to eccentric exercise can occur in the absence of significant muscle damage. Exposure to a small number of nondamaging eccentric contractions can significantly improve recovery after a subsequent damaging eccentric bout. Furthermore, this adaptation appears to be mode-specific and not applicable to concentric contractions.     

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.     

En bloc control of deep and superficial thoracic muscles in sagittal loading and unloading of the trunk

External perturbation of the trunk via sudden loading and unloading is an established method to study control of spinal stability and postural equilibrium. As differential control of the deep and superficial lumbar multifidus occurs during predictable sagittal loading, we hypothesized that the deep and superficial components of the thoracic paraspinal muscles would also be differentially active during loading and unloading of the trunk. Variation in sagittal mobility between regions of the thorax and previous data of differences in control of the thoracic paraspinal muscles between regions in other tasks supported a hypothesis that there would be region-specific differences in responses to loading and unloading. This study used fine-wire electrodes to record electromyographic (EMG) activity from the right deep (multifidus/rotatores) and superficial (longissimus) muscles at T5, T8, and T11 in ten healthy subjects during predictable and unpredictable sudden loading and unloading of the trunk. EMG amplitude was calculated during 10 ms epochs for 50 ms before the onset of trunk perturbation and 150 ms after the perturbation. Contrary to our hypotheses, deep and superficial thoracic paraspinal muscles were similarly active (loading: p=0.470; unloading: p=0.137) and similarly affected by the degree of predictability at all levels. Thus, deep and superficial thoracic paraspinal muscles are recruited en bloc during sagittal plane trunk perturbations. This contrasts previous findings of differential control between the deep and superficial thoracic paraspinal muscles during rotational tasks, and provides evidence that discrete control of thoracic paraspinal muscle fascicles is specific to the direction of forces applied to the trunk.     

Effects of prior exercise on eccentric exercise-induced neutrophilia and enzyme release

PURPOSE: The purpose of this study was to determine the effects of prior exercise on changes in circulating neutrophils, neutrophil activation, and myocellular enzymes following a standardized bout of eccentric exercise. METHODS: Twenty-four male volunteers were randomized into three groups (N = 8). Group C performed 10 sets of 10 eccentric contractions of the quadriceps muscles with both legs (100% of the concentric IRM). Group D and Group F exercised for 2 h at 56%VO2max on a cycle ergometer followed by a similar bout of eccentric contractions. Group F also received 7.5 mL x kg(-1) of a carbohydrate-electrolyte beverage every 30 min during the submaximal exercise, whereas group D received no fluid. RESULTS: Body weight remained unchanged in groups C and F and decreased in group D by 1.56 +/- 0.34 kg. Ultrastructural Z-Band damage increased three-fold following exercise and remained elevated 3 d after exercise but was not different among groups. Circulating neutrophils were elevated more in group D compared with those in group C immediately after the exercise or rest period, and this difference persisted 3 h after the eccentric exercise. Serum lactoferrin concentrations increased 3.3-fold after exercise in all groups (P < 0.01). Creatine kinase levels (CK) rose in all subjects, with subjects in Group F and D having a significantly greater rise in CK after exercise compared with those in group C. CONCLUSIONS: These data indicate that submaximal exercise followed by a bout of eccentric exercise results in similar amounts of myofibrillar injury with a larger neutrophil response and CK release.     

The effects of a prolonged running exercise on strength characteristics

The aim of this study was to examine concentric, isometric, and eccentric strength reductions in the quadriceps muscle following a prolonged running exercise. Before and after a 2 h run (28.4+/-1.4 km) peak torque (PT) of the knee extensors at angular velocities of -120, -90, -60, 0, 60, 120, 180, 240 degrees x s(-1) using an isokinetic dynamometer, electromyographic (EMG) activity of the vastus lateralis (VL) and vastus medialis (VM) muscles and height of a counter movement jump were recorded in twelve well-trained triathletes. Counter movement jump performances decreased by 10% and PT values were all significantly lower (p < 0.01) at each angular velocity following the run. The torque loss was significantly (p < 0.01) greater under eccentric contractions (from 18 to 21%) than under concentric ones (from 11 to 14%). EMG activity (RMS) was lower in both VL and VM muscles after the 2 h run but no difference existed in RMS losses between concentric and eccentric contractions. The present results demonstrate that 1) a prolonged running exercise more greatly affects eccentric force production in the quadriceps muscle, and 2) this specificity seems to be due to an impairment of the muscular contractile mechanism rather than a modification to the neural input.     

Time course of mechanical and neuromuscular characteristics of cyclists and triathletes during a fatiguing exercise

This study examined the impact of sport specificity on the time course of fatigue during maximal voluntary eccentric, concentric and isometric torque production following a submaximal isokinetic fatiguing exercise. Seven cyclists and seven triathletes performed a fatiguing exercise consisting of nine sets of 31 isokinetic concentric knee extensions at 1.05 rad . s (-1). Fatigue was assessed pre-exercise, after three and six sets, and post-exercise. The maximal knee extension torque associated with electromyographic (EMG) activity was recorded during voluntary contractions and electrically induced contractions (single and paired twitches). The maximal voluntary eccentric torque production declined in cyclists (18 +/- 3.5 %, p < 0.05) and was not significantly affected in triathletes (5 +/- 2.5 %, p > 0.05). The decrease in cyclists was associated with an increase in the sum of the normalized EMG (nRMS) values of the three agonist muscles (p < 0.01). Although no significant difference was observed between groups, the two-way repeated-measure analysis of variance revealed a time effect on maximal concentric and isometric torque, twitch contractile and electrophysiological response (M (max)) properties. No modification in the activation and coactivation levels was observed. In conclusion, these results indicate that the time course of fatigue, especially during eccentric contractions, is mediated by sport-specific adaptations likely due to the mode of muscle contraction used in the activity.     

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.     

Influence of acute eccentric exercise on the H:Q ratio

The purpose of the present study was to examine the effects of an acute bout of eccentric exercise on maximal isokinetic concentric peak torque (PT) of the leg flexors and extensors and the hamstrings-to-quadriceps (H:Q) strength ratio. Sixteen male (mean±SD: age=20.9±2 years; stature=177.0±4.4 cm; mass=76.8±10.0 kg) volunteers performed maximal, concentric isokinetic leg extension and flexion muscle actions at 60°·sec?-?1 before and after (24-72 h) a bout of eccentric exercise. The eccentric exercise protocol consisted of 4 sets of 10 repetitions for the leg press, leg extension, and leg curl exercises at 120% of the concentric one repetition maximum (1-RM). The results indicated that the acute eccentric exercise protocol resulted in a significant (P<0.05) decrease in isokinetic leg flexion (13-19%) and leg extension (11-16%) PT 24-72 h post-exercise. However, the H:Q ratios were unaltered by the eccentric exercise protocol. These findings suggest that an acute bout of eccentric exercise utilizing both multi - and single - joint dynamic constant external resistance (DCER) exercises results in similar decreases in maximal isokinetic strength of the leg flexors and extensors, but does not alter the H:Q ratio.     

Central versus peripheral adaptations following eccentric resistance training

Aim of the present investigation was to study the effects of an eccentric training on the neuromuscular properties of the plantar-flexor muscles. The experiment was carried out on 14 males divided into two groups (eccentric and control). Eccentric training consisted of six sets of six eccentric contractions at 120 % of one maximal concentric repetition and it was performed four times a week during four weeks. Before and after the 4-wk period, the plantar-flexor torque and the associated electromyographic activity were recorded during voluntary contractions (isometric, concentric and eccentric) and electrically induced contractions (twitch and tetanus), in order to distinguish central from peripheral adaptations. For the eccentric group, voluntary torque significantly increased after training independent of the action mode (relative gains 14 - 30 %, p < 0.05). This was associated with an increase in agonist EMG activity during isometric action and a decrease in antagonist coactivation in concentric (-27 %) and eccentric actions (-22 %) (p < 0.05). Voluntary activation level significantly increased from 80 +/- 5 % to 91 +/- 2 % (p < 0.05). Some of the twitch contractile properties (peak torque and maximal rate of twitch tension relaxation) were significantly modified (p < 0.05), but no changes were observed for the tetanus characteristics. These results allowed to conclude that the torque gains observed after the present training were more likely associated to central adaptations, affecting both agonist and antagonist muscles.     

Prior muscular exercise affects cycling pattern

The aim of this study was to investigate the effect of concentric or eccentric fatiguing exercise on cycling pattern. Eleven well trained cyclists completed three sessions of cycling (control cycling test [CTRL], cycling following concentric [CC] or eccentric [ECC] knee contractions) at a mean power of 276.8 +/- 26.6 Watts. Concentric and eccentric knee contractions were performed at a load corresponding to 80 % of one repetition maximum with both legs. Before and after CTRL, CC or ECC knee contractions and after cycling, a maximal voluntary contraction (MVC) test was performed. Cardiorespiratory, mechanical and electromyographic activity (EMG) of the rectus femoris, vastus lateralis and biceps femoris muscles were recorded during cycling. A significant decrease in MVC values was observed after CC and ECC exercises and after the cycling. ECC exercise induced a significant decrease in EMG root mean square during MVC and a decrease in pedal rate during cycling. EMG values of the three muscles were significantly higher during cycling exercise following CC exercise when compared to CTRL. The main finding of this study was that a prior ECC exercise induces a greater neuromuscular fatigue than a CC exercise, and changes in cycling pattern.     

Muscle functional MRI analysis of trunk muscle recruitment during extension exercises in asymptomatic individuals

The present study examined the activity levels of the thoracic and lumbar extensor muscles during different extension exercise modalities in healthy individuals. Therefore, 14 subjects performed four different types of extension exercises in prone position: dynamic trunk extension, dynamic–static trunk extension, dynamic leg extension, and dynamic–static leg extension. Pre‐ and post‐exercise muscle functional magnetic resonance imaging scans from the latissimus dorsi, the thoracic and lumbar parts of the longissimus, iliocostalis, and multifidus were performed. Differences in water relaxation values (T2‐relaxation) before and after exercise were calculated (T2‐shift) as a measure of muscle activity and compared between extension modalities. Linear mixed‐model analysis revealed higher lumbar extensor activity during trunk extension compared with leg extension (T2‐shift of 5.01 ms and 3.55 ms, respectively) and during the dynamic–static exercise performance compared with the dynamic exercise performance (T2‐shift of 4.77 ms and 3.55 ms, respectively). No significant differences in the thoracic extensor activity between the exercises could be demonstrated. During all extension exercises, the latissimus dorsi was the least activated compared with the paraspinal muscles. While all extension exercises are equivalent effective to train the thoracic muscles, trunk extension exercises performed in a dynamic–static way are the most appropriate to enhance lumbar muscle strength.     

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.     

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.     

Exercise-induced signs of muscle overuse in children

Signs of overuse after intense muscular exertion are well described in adults, while little research has been conducted in children. The aim of the study was to investigate some indirect markers of muscle damage in 13 years old boys following two different protocols of one-leg stepping exercise to exhaustion. This stepping exercise was performed by two experimental groups with different contributions of concentric and eccentric contractions in a 1:1 vs 1:2 ratio of timing. Subjective soreness perception and maximum voluntary isometric force of the knee extensor muscles were measured immediately prior to and immediately following the exercise, and at 1, 3, 24, 48, 72, 96 hours post exercise. Metabolic markers of exercise stress were taken at similar time intervals and included plasma glutathione concentrations as a marker for oxidative stress, circulating leukocyte numbers, and plasma creatine kinase (CK) activity. All parameters studied demonstrated a higher level of muscular exertion, with more evident signs of overuse in the group with the more eccentric contribution. Complete recovery was achieved between 72 and 96 hours after exertion. However, in this group of boys, the CK activity did not show the typical adult-like increase. Therefore the wide use of CK as an indicator of intense muscle exertion was not supported in this group of children. It can be concluded that children, like adults, experience similar degrees of muscle disturbances following intense exercise and that they may recover more quickly from such exercise.     

Characteristics of isometric and dynamic strength loss following eccentric exercise-induced muscle damage

Angle-specific isometric strength and angular velocity-specific concentric strength of the knee extensors were studied in eight subjects (5 males and 3 females) following a bout of muscular damaging exercise. One hundred maximal voluntary eccentric contractions of the knee extensors were performed in the prone position through a range of motion from 40 degrees to 140 degrees (0 degrees = full extension) at 1.57 rads(-1). Isometric peak torque was measured whilst seated at 10 degrees and 80 degrees knee flexion, corresponding to short and optimal muscle length, respectively. Isokinetic concentric peak torque was measured at 0.52 and 3.14 rad x s(-1). Plasma creatine kinase (CK) activity was also measured from a fingertip blood sample. These measures were taken before, immediately after and on days 1, 2, 4, and 7 following the eccentric exercise. The eccentric exercise protocol resuited in a greater relative loss of strength (P< 0.05) at short muscle length (76.3 +/- 2.5% of pre-exercise values) compared to optimal length (82.1 +/- 2.7%). There were no differences in the relative strength loss between isometric strength at optimal length and isokinetic concentric strength at 0.52 and 3.14 rad x s(-1). CK activity was significantly elevated above baseline at days 4 (P < 0.01) and 7 (P < 0.01). The greater relative strength loss at short muscle length appeared to persist throughout the seven-day testing period and provides indirect evidence of a shift in the angle-torque relationship towards longer muscle lengths. The results lend partial support to the popping sarcomere hypothesis of muscle damage, but could also be explained by an impairment of activation at short muscle lengths.     

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.     

Rate of force development as a measure of muscle damage

This study tested the hypothesis that rate of force development (RFD) would be a more sensitive indirect marker of muscle damage than maximum voluntary isometric contraction (MVC) peak torque. Ten men performed one concentric cycling and two eccentric cycling (ECC1, ECC2) bouts for 30 min at 60% of maximal concentric power output with 2 weeks between bouts. MVC peak torque, RFD, and vastus lateralis electromyogram amplitude and mean frequency were measured during a knee extensor MVC before, immediately after and 1–2 days after each bout. The magnitude of decrease in MVC peak torque after exercise was greater (P < 0.05) for ECC1 (11–25%) than concentric cycling (2–12%) and ECC2 (0–16%). Peak RFD and RFD from 0–30 ms, 0–50 ms, 0–100 ms, to 0–200 ms decreased (P < 0.05) immediately after all cycling bouts without significant differences between bouts, but RFD at 100–200 ms interval (RFD_100–200) decreased (P < 0.05) at all time points after ECC1 (24–32%) and immediately after ECC2 (23%), but did not change after CONC. The magnitude of decrease in RFD_100–200 was 7–19% greater than that of MVC peak torque after ECC1 (P < 0.05). It is concluded that RFD_100–200 is a more specific and sensitive indirect marker of eccentric exercise‐induced muscle damage than MVC peak torque.