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.     

Muscle conduction velocity,strength, neural activity,and morphological changes after eccentric and concentric training

This study compared the effects of concentric and eccentric training on neuromuscular adaptations in young subjects. Twenty‐two men and women were assigned to one of two groups: concentric (CON, n = 11) and eccentric (ECC, n = 11) training. Training consisted of 6 weeks of isokinetic exercise, performed twice weekly, starting with two sets of eight repetitions, and progressing to five sets of 10 repetitions. Subjects were tested in strength variables [concentric, eccentric, and isometric peak torque (PT), and rate of force development (RFD)], muscle conduction velocity (CV), neuromuscular activity, vastus lateralis (VL) muscle thickness, and echo intensity as determined by ultrasonography. There were similar increases in the concentric and eccentric PTs in both the CON and ECC groups (P < 0.01), but only the ECC group showed an increase in isometric PT (P < 0.001). Similarly, both groups exhibited increased VL muscle thickness, CV, and RFD, and reduced VL echo intensity (P < 0.05). Significant correlations were observed among the relative changes in the neuromuscular outcomes and training variables (e.g., total work, average PT) (r = 0.68–0.75, P < 0.05). The results showed that both training types similarly improved dynamic PT, CV, RFD, and muscle thickness and quality during the early weeks of training.     

Effects of age on the reciprocal peak torque ratios during knee muscle contractions in elite soccer players

To investigate the effects of age on the reciprocal peak torque ratios during knee muscle contractions, 25 elite male soccer players, aged 22.3 +/- 3.8 yr (18-28), volunteered for the present study. The players were grouped as adult (> 21 years, n = 13) and young players (< or = 21 years, n = 12). Maximal concentric (CON) and eccentric (ECC) isokinetic thigh muscle strength was measured at angular velocities of 30 degrees, 180 degrees, 240 degrees and 300 degrees/s. ECC and CON peak torques of knee flexors (hamstring, HAM) and CON peak torques of knee extensors (quadriceps, QUA) in the dominant knee were greater (P < 0.05) in adult players than in young players at 180, 240 and 300 degrees/s. ECC HAM/CON QUA peak torque ratio at 300 degrees/s was greater (P < 0.05) for adult players compared to young players in the dominant knee but not in the nondominant knee. Furthermore, conventional HAM/QUA peak torque ratios of the dominant knee at all angular velocities for ECC contraction were higher (P < 0.05) in adult players than in young players. In conclusion, the findings of the present study indicate that the reciprocal torque ratio is influenced by age in the dominant knee of elite soccer players. Because there was no effect of age for the nondominant leg, the findings of the present study are more likely to be the result of the training background of the players than their age.     

Strength after bouts of eccentric or concentric actions.

This study examined the influence of an initial bout of eccentric or concentric actions and a subsequent bout of eccentric actions on muscular strength. Twenty-four healthy males, 24-45 yr old, were placed in three groups that performed eccentric actions in bouts 1 and 2 (ECC/ECC, N = 8), concentric actions in bout 1, and eccentric actions in bout 2 (CON/ECC, N = 8) or served as controls (N = 8). Bouts involved unilateral actions with the left and right quadriceps femoris. Ten sets of 10 repetitions with an initial resistance equal to 85% of the eccentric or concentric one repetition maximum (1 RM) were performed for each bout. Three minutes of rest were given between sets and 3 wk between bouts. Two weeks before bout 1 and 1, 4, 7, and 10 d after bouts 1 and 2, eccentric and concentric 1 RM were measured for the right quadriceps femoris and a speed-torque relation established for the left quadriceps femoris. Eccentric and concentric 1 RM decreased (P less than 0.05) 32% 1 d after bout 1 for group ECC/ECC. The speed-torque relation was down-shifted (P less than 0.05) 38%. Eccentric 1 RM and eccentric and isometric torque returned to normal 6 d later. Concentric 1 RM and torque at 3.14 rad.s-1 had not recovered on day 10 (-7% for both, P less than 0.05). Decreases in strength after bout 2 for group ECC/ECC only occurred on day (-9% for concentric 1 RM and 16% downshift of the speed-torque relation).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Shift of peak torque angle after eccentric exercise

This study aims to investigate the changes in the mechanical properties of quadriceps muscle following a sub-maximal concentric-eccentric stepping exercise protocol. Twenty-four untrained healthy subjects aged 21.9 +/- 0.55 years were asked to perform a 10-minute stepping exercise where the dominant leg worked eccentrically and the non-dominant leg worked concentrically at a rate of 15 cycles/min. The quadriceps isokinetic peak torque and the corresponding peak torque angle at angular velocity of 60 degrees /sec, and muscle soreness were determined at baseline, immediately after, day 1 and day 2 after the exercise protocol. Repeated measures of ANOVA showed no change in the peak torque after the eccentric exercise and concentric exercise (p > 0.05). There was a significant shift in the peak torque angle to longer muscle lengths in the eccentrically-exercised leg immediately (65.6 +/- 2.21 degrees ) and on the following two days after exercise (day 1: 68.3 +/- 2.71 degrees ; day 2: 67.4 +/- 2.51 degrees ) when compared with baseline (61.4 +/- 1.55 degrees , p < 0.05). These features were not observed in the concentrically-exercised leg. Eccentric exercise produced a higher level of soreness than concentric exercise at day 1 and 2 after the protocol. Submaximal eccentric exercise could bring about changes in the muscle properties resulting in a shift in the angle-torque relationship to longer muscle length without significant force deficit.     

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.     

Functional eccentric-concentric ratio of knee extensors and flexors in pre-pubertal children, teenagers and adult males and females

The purpose of this study was to examine the age and sex associated differences in the eccentric/concentric functional ratio for the knee. Isokinetic concentric and eccentric knee extension and flexion was measured at 0.52 rad x s (-1) and 3.14 rad x s (-1) in 121 subjects. Other than mass there were no significant age-by-sex interaction effects for all variables examined. A significant velocity-by-age group effect was demonstrated for ECC (KF)/CON (KE) with higher ratios at 3.14 compared to 0.52 rad x s (-1). Females' CON (KF)/ECC (KE) was significantly lower than males at both velocities. Adults demonstrated significantly lower CON (KF)/ECC (KE) than the teenagers at 0.52 rad x s (-1) and lower than the prepubertal and teenager groups at 3.14 rad x s (-1). However, for ECC (KF)/CON (KE) at 3.14 rad x s (-1), prepubertal ratios were significantly lower than teenagers and adults. The results of the current study suggest that functional rather than conventional ratio should be used when examining knee stability. During fast velocity movements, prepubertal children have a lower capacity for generating eccentric compared to concentric torque. The lower CON (KF)/ECC (KE) ratio in adults appears to be due to a greater ability to generate large eccentric torques at all slow and fast movement velocities. The lower CON (KF)/ECC (KE) ratio in females is a product of lower concentric torque as opposed to high eccentric torque producing capability as previously thought.     

Neuromuscular fatigue profile in endurance-trained and power-trained athletes

PURPOSE: This study examined the effects of training background on the relationship between the neuromuscular fatigue profile and maximal voluntary torque production in isometric, concentric, and eccentric contraction modes. METHODS: Before and after three sets of 31 isokinetic concentric knee extensions at 60 degrees .s(-1), voluntary and electrically induced contractions were recorded in 14 endurance-trained (ENDU) men (seven cyclists: age 25 +/- 2 yr, mass 70 +/- 8 kg, height 175 +/- 5 cm; and seven triathletes: age 27 +/- 4 yr, mass 71 +/- 5 kg, height 179 +/- 6 cm) and seven explosive power-trained men (EXPLO: age 24 +/- 1 yr, mass 73 +/- 5 kg, height 179 +/- 4 cm). Maximal knee-extension torque, activation level (twitch interpolation technique), electromyographic activity of agonist and antagonist muscles, and twitch contractile properties were assessed. RESULTS: At preexercise, the maximal voluntary isometric and concentric torques of EXPLO were greater than those of ENDU (P < 0.05). After the fatiguing exercise, significant isometric (18%; P < 0.01) and concentric (25%; P < 0.05) torque decreases in EXPLO were associated with, respectively, twitch torque (Pt) and maximal rate of twitch development (+dPt/dt) reductions (P < 0.01) and with an increase in the antagonist coactivation level (P < 0.01). No modification was observed for ENDU. Interestingly, the coactivation level was also increased (P < 0.01) in eccentric contraction for EXPLO, although the maximal eccentric torque decrease (P < 0.01) could not be specifically attributed to any group. CONCLUSION: The fatiguing exercise induced central and peripheral adaptations, but the mechanisms differed regarding the contraction mode. At pre- and postfatiguing exercise, it seems that the neuromuscular profile depends on the subject's training background and the contraction modes used to assess fatigue.     

Eccentric exercise in coronary patients: central hemodynamic and metabolic responses

PURPOSE: With lengthening (eccentric) muscle contractions, the magnitude of locomotor-muscle mass and strength increase has been demonstrated to be greater compared with shortening (concentric) muscle contractions. In healthy subjects, energy demand and heart rate responses with eccentric exercise are small relative to the amount of muscle force produced. Thus, eccentric exercise may be an attractive alternative to resistance exercise for patients with limited cardiovascular exercise tolerance. METHODS: We tested the cardiovascular tolerance of eccentric exercise in 13 coronary patients (ages 40-66) with preserved and/or mild reduced left ventricular function. Patients were randomly assigned to either an eccentric (ECC; N = 7) or a concentric (CON; N = 6) training group and trained for 8 wk. Training workload was increased progressively (from week 1 to 5) to an intensity equivalent to 60% [OV0312]O(2peak). RESULTS: On average, maximum power output achieved with ECC was fourfold compared with CON (357 +/- 96 W vs 97 +/- 21 W; P < 0.005), whereas measures of oxygen uptake and blood lactate were significantly lower (P < 0.05 each), and ratings of perceived exertion were similar for ECC and CON. During a 20-min session of ECC and CON, central hemodynamics was measured by means of right heart catheterization. During ECC, responses of mean arterial blood pressure, systemic vascular resistance, pulmonary capillary pressure, cardiac index, and stroke work of the left ventricle on average were in the normal range of values and similar to those observed during CON. Compared with baseline, after 8 wk of training, echocardiographic left ventricular function was unchanged. CONCLUSION: The results indicate uncoupling of skeletal muscle load and cardiovascular stress during ECC. For low-risk patients with coronary heart disease without angina, inducible ischemia, or left ventricular dysfunction, ECC can be recommended as a safe new approach to perform high-load muscular exercise training with minimal cardiovascular stress.     

Specific effects of eccentric training on muscular fatigability

This study was designed to test the hypothesis that an eccentric training period induces a reduction of neuromuscular fatigability following an eccentric exercise. Before (Pre-T) and after (Post-T) a 7-wks sub-maximal eccentric training, ten active males performed a fatiguing exercise consisting of five sets of ten maximal eccentric elbow flexions. Before (Pre-T-1 and Post-T-1) and after (Pre-T-2 and Post-T-2) each fatiguing exercise, the voluntary torque and its associated agonistic electromyographic activity (RMS), assessed at four angular velocities (-60 degrees x s (-1); 0 degrees x s (-1); 60 degrees x s (-1); 240 degrees x s (-1)) were measured. The isometric voluntary activation level and twitch contractile properties were measured. The training period induced significant eccentric and isometric torque gains. While isometric and concentric torque decreases were similar Pre-T-2 and Post-T-2, the eccentric torque loss was significantly lower Post-T-2 than Pre-T-2 (-11.7 +/- 10.2 % and -20.5 +/- 6.5 %, respectively; p < 0.05). The reduction of the twitch maximal rate of torque rise was also significantly lower Post-T-2 (-49.4 +/- 11.9 %) than Pre-T-2 (-65.2 +/- 9.8 %) (p < 0.05). The loss of maximal voluntary activation and RMS were similar Pre-T-2 and Post-T-2. The present experiment showed that a 7-wks eccentric training period produced contraction-type specific adaptations that significantly reduced the exercise-induced torque loss during eccentric muscle actions.     

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.     

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.     

A 10-week randomized trial comparing eccentric vs. concentric hamstring strength training in well-trained soccer players

PURPOSE: To compare the effects of a 10-week training program with two different exercises -- traditional hamstring curl (HC) and Nordic hamstrings (NH), a partner exercise focusing the eccentric phase -- on muscle strength among male soccer players. METHODS: Subjects were 21 well-trained players who were randomized to NH training (n = 11) or HC training (n = 10). The programs were similar, with a gradual increase in the number of repetitions from two sets of six reps to three sets of eight to 12 reps over 4 weeks, and then increasing load during the final 6 weeks of training. Strength was measured as maximal torque on a Cybex dynamometer before and after the training period. RESULTS: In the NH group, there was an 11% increase in eccentric hamstring torque measured at 60 degrees s(-1), as well as a 7% increase in isometric hamstring strength at 90 degrees, 60 degrees and 30 degrees of knee flexion. Since there was no effect on concentric quadriceps strength, there was a significant increase in the hamstrings:quadriceps ratio from 0.89 +/- 0.12 to 0.98 +/- 0.17 (11%) in the NH group. No changes were observed in the HC group. CONCLUSION: NH training for 10 weeks more effectively develops maximal eccentric hamstring strength in well-trained soccer players than a comparable program based on traditional HC.     

Contralateral effects of eccentric resistance training on immobilized arm

This study compared the effects of contralateral eccentric‐only (ECC) and concentric‐/eccentric‐coupled resistance training (CON‐ECC) of the elbow flexors on immobilized arm. Thirty healthy participants (18‐34 y) were randomly allocated to immobilization only (CTRL; n = 10), immobilization and ECC (n = 10), or immobilization and CON‐ECC group (n = 10). The non‐dominant arms of all participants were immobilized (8 h·day^?1) for 4 weeks, during which ECC and CON‐ECC were performed by the dominant (non‐immobilized) arm 3 times a week (3‐6 sets of 10 repetitions per session) with an 80%‐120% and 60%‐90% of one concentric repetition maximum (1‐RM) load, respectively, matching the total training volume. Arm circumference, 1‐RM and maximal voluntary isometric contraction (MVIC) strength, biceps brachii surface electromyogram amplitude (sEMG_RMS), rate of force development (RFD), and joint position sense (JPS) were measured for both arms before and after immobilization. CTRL showed decreases (P < .05) in MVIC (?21.7%), sEMG_RMS (?35.2%), RFD (?26.0%), 1‐RM (?14.4%), JPS (?87.4%), and arm circumference (?5.1%) of the immobilized arm. These deficits were attenuated or eliminated by ECC and CON‐ECC, with greater effect sizes for ECC than CON‐ECC in MVIC (0.29: +12.1%, vs ?0.18: ?0.1%) and sEMG_RMS (0.31:17.5% vs ?0.15: ?5.9%). For the trained arm, ECC showed greater effect size for MVIC than CON‐ECC (0.47 vs 0.29), and increased arm circumference (+2.9%), sEMG_RMS (+77.9%), and RDF (+31.8%) greater (P < .05) than CON‐ECC (+0.6%, +15.1%, and + 15.8%, respectively). The eccentric‐only resistance training of the contralateral arm was more effective to counteract the negative immobilization effects than the concentric‐eccentric training.     

The influence of age on isokinetic torque of the upper and lower leg musculature in sedentary men.

While strength patterns in aging for the knee joint have been well investigated in the concentric mode, few data are available about the behaviour in the eccentric mode and for either modus in the ankle. The purpose of this study was to compile reference data for the lower extremities in untrained men between 20 and 60 years of age to determine the influence of age, especially in the eccentric work mode. Sixty-four male subjects between 20 and 60 years were divided into four age groups. Using a LIDO ACTIVE dynamometer, maximum torque was tested for the knee between 90 degrees to 0 degrees and for the ankle between 30 degrees to -10 degrees at velocities 60, 180, 240, 300 degrees/s concentric, 60 and 120 degrees/s eccentric and isometric with angles 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees for the knee and 30 degrees, 20 degrees, 10 degrees, 0 degrees , -10 degrees for the ankle. Individual parameters for age-dependence were checked using linear correlation calculation with p < 0.01 set as significant. The peak torque (PT) of the knee extensors and flexors showed a typical course with the highest values in the eccentric and isometric mode and a decrease in the concentric mode with increasing angular velocity. In the concentric mode there was a significant negative correlation between PT and age at all angular velocities, but none for isometric and eccentric mode. The greatest maximum torque in the ankle was attained in the eccentric mode at 60 degrees/s. The difference to the knee was smallest in this mode compared to isometric and concentric. The plantar flexion showed age-dependence at all concentric velocities, less in eccentric and none in isometric mode. There was no correlation in dorsiflexion. The influence of loss of muscle fiber and degeneration in the course of aging has thus less influence in eccentric measurements than in the concentric mode. On the contrary, it must be assumed that the high eccentric tensions which are possible due to the quasi-elastic structures in the muscle, are maintained by the increase in stiffness of the connective tissue.     

Deficits in eccentric versus concentric torque in children with spastic cerebral palsy

PURPOSE: The purposes of this study were to determine whether ambulatory children with spastic cerebral palsy (CP) had abnormal isokinetic eccentric peak torque values at the knee and ankle, and to gain further insights on the influence of spasticity on voluntary force production in this population. METHODS: Twenty-four children with spastic CP (mean = 11.1+/-2.6 yr) and twenty children of comparable age with no neuromotor pathology (mean = 10.3+/-2.6 yr) participated in an isokinetic testing protocol on a Biodex dynamometer that measured eccentric and concentric peak torques of the knee extensors, knee flexors, ankle dorsiflexors, and ankle plantarflexors. Angular velocity of the eccentric trials was 30 degrees x s(-1) and of the concentric trials was 30 degrees x s(-1), 60 degrees x s(-1), and 120 degrees x s(-1). Peak torque values were normalized by body weight and compared across groups by using ANOVA procedures. Eccentric to concentric (E/C) peak torque ratios at 30 degrees x s(-1) were computed for each muscle and compared across groups. The torque values in CP were also expressed as a percent of the mean normalized value of the comparison group and compared across conditions using repeated measures ANOVA (P < 0.05). RESULTS: Children with CP demonstrated decreased eccentric and concentric peak torques for all muscle groups tested. The relative deficit in eccentric torque was less than the concentric torque and the decrement in concentric torque across speeds was greater in CP for all muscle groups except the ankle dorsiflexors. The E/C ratios for the knee extensors and flexors were also greater in CP. CONCLUSIONS: Children with CP have diminished eccentric as well as concentric peak torques at the knee and ankle. The influence of spasticity on voluntary force production can be inferred from the bias toward greater eccentric torque and the greater decrement in concentric torque across speeds in children with spastic CP.     

Evidence of neuromuscular fatigue after prolonged cycling exercise

PURPOSE: The purpose of this study was to analyze the effects of prolonged cycling exercise on metabolic, neuromuscular, and biomechanical parameters. METHODS: Eight well-trained male cyclists or triathletes performed a 2-h cycling exercise at a power output corresponding to 65% of their maximal aerobic power. Maximal concentric (CON; 60, 120, 240 degrees x s(-1)), isometric (ISO; 0 degrees s(-1)), and eccentric (ECC; -120, -60 degrees x s(-1)) contractions, electromyographic (EMG) activity of vastus lateralis (VL) and vastus medialis (VM) muscles were recorded before and after the exercise. Neural (M-wave) and contractile (isometric muscular twitch) parameters of quadriceps muscle were also analyzed using electrical stimulation techniques. RESULTS: Oxygen uptake (VO2), minute ventilation (VE), and heart rate (HR) significantly increased (P < 0.01) during the 2-h by, respectively, 9.6%, 17.7%, and 12.7%, whereas pedaling rate significantly decreased (P < 0.01) by 21% (from 87 to 69 rpm). Reductions in muscular peak torque were quite similar during CON, ISO, and ECC contractions, ranging from 11 to 15%. M-wave duration significantly increased (P < 0.05) postexercise in both VL and VM, whereas maximal amplitude and total area decreased (VM: P < 0.05, VL: NS). Significant decreases in maximal twitch tension (P < 0.01), total area of mechanical response (P < 0.01), and maximal rate of twitch tension development (P < 0.05) were found postexercise. CONCLUSIONS: A reduction in leg muscular capacity after prolonged cycling exercise resulted from both reduced neural input to the muscles and a failure of peripheral contractile mechanisms. Several hypothesis are proposed to explain a decrease in pedaling rate during the 2-h cycling with a constancy of power output and an increase in energy cost.     

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.     

膝关节屈肌和伸肌等速向心、等速离心及等长测试的研究

本文通过运用Ｃｙｂｅｘ－６０００型等速测力系统对２５名健康男青年膝屈肌和伸肌进行等速向心、等速离心及等长测试，来比较膝肌肉向心收缩、离心收缩和等长收缩的功能，并探讨其相互间的关系。结果表明：等速测试时，膝屈肌和伸肌离心收缩的肌力明显大于向心收缩。在膝屈曲６０°时，离心收缩和等长收缩的肌力同样明显大于向心收缩，但离心收缩与等长收缩相比无显著性差异。随运动速度增加，屈肌和伸肌向心收缩的肌力明显下降，而离心收缩的肌力无明显变化。