Effects of hyperbaric oxygen on a human model of injury.

To determine whether intermittent exposures to hyperbaric oxygen enhance recovery from delayed-onset muscle soreness of the quadriceps, we conducted a randomized, controlled, double-blinded, prospective study using 66 untrained men between the ages of 18 and 35 years. After the induction of muscle soreness, these subjects were treated in a hyperbaric chamber over a 5-day period in two phases, with four groups (control, hyperbaric oxygen treatment, delayed treatment, and sham treatment) in the first phase; and three groups (3 days of treatment, 5 days of treatment, and sham treatment) in the second phase. The hyperbaric exposures involved 100% oxygen for 1 hour per day at 2.0 atm. The sham treatments involved 21% oxygen for 1 hour per day at 1.2 atm. We monitored recovery using a leg dynamometer to test eccentric torque of the nondominant quadriceps muscle before and immediately after exercise and at 48 and 96 hours after exercise. Pain was tested daily using visual analog pain scales. In phase 1 a significant difference in recovery of eccentric torque was noted in the treatment group compared with the other groups. In phase 2, the recovery of eccentric torque for the 5-day treatment group was significantly greater than for the sham group from immediately after exercise to 96 hours after exercise. The pain data did not differ significantly in any comparison in either phase. The results suggest that treatment with hyperbaric oxygen may enhance recovery of eccentric torque of the quadriceps muscle from delayed-onset muscle soreness.     

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.     

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.     

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.     

Progressive resistance training temporarily alters hamstring torque-angle relationship

To examine the effects of eccentric and concentric progressive resistance training on muscle torque-angle relationship, 30 young adults were randomly allocated into three groups of 10, control (CTL), eccentric training (ECC) and concentric training (CON). The ECC and CON groups performed seven sessions over 3 weeks of progressive resistance training of the right hamstrings muscle, using a standard barbell and a leg curl machine. Torque-angle relationship was measured before and 4, 11 and 18 days after the end of training. Voluntary isometric torque was recorded at seven test angles, with the subject prone (20-80 degrees; 0 degrees is full extension). In the CON group, the angle of peak isometric torque increased from 46.0 +/- 5.2 degrees pre-training to 53.0 +/- 14.9 degrees on day 4 following training (P<0.05). In the ECC group, peak torque was increased over baseline on days 4 and 11 post-training, particularly at extended knee angles (P<0.05). The angle at which peak torque occurred was decreased on day 4 (50.0 +/- 8.2 degrees pre-training, 29.0 +/- 7.4 degrees on day 4) and on day 11 (both P<0.01), but was similar to baseline 18 days after training. ECC therefore induced a temporary change in torque-angle relationship.     

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.     

Quadriceps concentric and eccentric exercise 1: Changes in contractile and electrical activity following eccentric and concentric exercise

The purpose of this study was to determine whether or not losses of strength or endurance following eccentric and concentric exercise are associated with reduced excitation. The effects of eccentric and concentric work on maximal voluntary isometric contraction (MVC) and surface electromyogram (EMG) of the quadriceps were studied in 10 healthy male subjects following bench-stepping for 20 min with a constant leading leg. Prior to stepping and at 0, 0.25, 0.50, 0.75, 1, 3, 24 and 48 h afterwards the subjects performed a 30 s leg extension MVC with each leg during which the isometric force and the root mean square voltage of the EMG were recorded. In the eccentrically exercised muscles (ECC), MVC0-3 (force during the first 3 s of contraction) fell immediately after the bench-stepping exercise to 88+/-2% (mean+/-SE) of the pre-exercise value and remained significantly lower than the concentrically exercised muscles (p<0.05). The muscle weakness in the ECC could not be attributed to central fatigue as surface EMG amplitude at MVC0-3 increased during the recovery period. Muscle weakness after eccentric exercise appears to be due to contractile failure, which is not associated with a reduction in excitation as assessed by surface EMG. Muscular fatigue over 30 s did not change in the two muscle groups after exercise (p = 0.79), indicating that the ECC were weaker but not more fatiguable after exercise.     

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.     

Quadriceps concentric and eccentric exercise 2: Differences in muscle strength, fatigue and EMG activity in eccentrically-exercised sore and non-sore muscles

The purpose of this study was to determine whether the previously reported muscle weakness and increases in EMG and EMG/force ratio after eccentric exercise were related to ensuing soreness or simply to the exercise mode. Delayed-onset muscle soreness, maximal voluntary force and the surface electromyogram (EMG) of the quadriceps were studied in 10 healthy male subjects following 20 min of bench-stepping with a constant leading leg. Prior to stepping and at 0, 0.25, 0.50, 0.75, 1, 3, 24 and 48 h afterwards the subjects performed a 30 s isometric maximal voluntary contraction (MVC) of the extensors of each leg during which the isometric force and the root mean square voltage of the surface EMG (rms EMG) were recorded. Muscle soreness was recorded prior to and at 0, 0.75, 3, 24 and 48 h after the stepping task by means of a force probe. No soreness was experienced in the concentrically exercised muscles, but in the eccentrically exercised muscles 5 subjects were not sore and 5 experienced soreness after 24 h, increasing to 48 h. There were no significant differences between sore and non-sore muscles in muscle weakness, fatigue during 30 s, the EMG amplitudes or the EMG/force ratios during peak force and the 30 s MVC (p >0.05). Muscle weakness following eccentric exercise was related to the exercise mode and was independent of subsequent soreness. Both weakness and soreness may be related to muscle damage, but involve different mechanisms.     

The effects of muscle damage on running economy in healthy males

Published information on aspects related to muscle damage and running economy is both limited and contradictory. To contribute to the current debate, we investigated the effects of an eccentric exercise session on selected muscle damage indices in relation to running economy using 10 (mean age 23 +/- 1 years) healthy male volunteers. The eccentric exercise session consisted of 120 (12 x 10) maximal voluntary repetitions by each randomly selected leg at the angular velocity of 1.05 rad . s (-1). Muscle damage (creatine kinase, delayed onset muscle soreness, range of movement, and eccentric, concentric and isometric [at 60 degrees and 110 degrees knee flexion] peak torque) and running economy (oxygen consumption, pulmonary ventilation, respiratory exchange ratio and breaths per minute during treadmill running at 133 and 200 m . min (-1)) indicators, were assessed pre-, 24-, 48-, 72- as well as 96-h after exercise. All muscle damage indicators revealed significant changes at almost all time-points of assessment compared to pre-exercise data (p < 0.05). However, none of the running economy parameters disclosed any significant change throughout the study (p > 0.05). It was concluded that changes in muscle damage and muscle performance as measured in this study are not reflected by concomitant alterations in running economy at submaximal intensities.     

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.     

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.     

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.     

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.     

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.     

The effect of passive stretching on delayed onset muscle soreness, and other detrimental effects following eccentric exercise

The aim of this study was to measure if passive stretching would influence delayed onset muscle soreness (DOMS), dynamic muscle strength, plasma creatine kinase concentration (CK) and the ratio of phosphocreatine to inorganic phosphate (PCr/Pi) following eccentric exercise. Seven healthy untrained women, 28–46 years old, performed eccentric exercise with the right m. quadriceps in an isokinetic dynamometer (Biodex, angle velocity: 60°. s⁻¹) until exhaustion, in two different experiments, with an interval of 13-23 months. In both experiments the PCr/P_i ratio, dynamic muscle strength, CK and muscle pain were measured before the eccentric exercise (day 0) and the following 7 d. In the second experiment daily passive stretching (3 times of 30 s duration, with a pause of 30 s in between) of m. quadriceps was included in the protocol. The stretching was performed before and immediately after the eccentric exercise at day 0, and before measurements of the dependent variables daily for the following 7 d. The eccentric exercise alone led to significant decreases in PCr/P_i ratio ( P <0.001) and muscle strength ( P <0.001), and an increase in CK concentration ( P <0.01). All subjects reported pain in the right m. quadriceps with a peak 48 h after exercise. There was no difference in the reported variables between experiments one and two. It is concluded that passive stretching did not have any significant influence on increased plasma- CK, muscle pain, muscle strength and the PCr/P_i ratio, indicating that passive stretching after eccentric exercise cannot prevent secondary pathological alterations.     

Effects of eccentric versus concentric training on thigh muscle strength and EMG

The purpose of this study was to compare pure eccentric and concentric strength training regarding possible specific effects of muscle action type on neuromuscular parameters, such as a decreased inhibition during maximal voluntary eccentric actions. Two groups of young healthy adult men performed 10 weeks of either eccentric or concentric unilateral isokinetic knee extensor training at 90 degrees.s(-1), 4 sets of 10 maximal efforts, 3 days a week. Knee extensor torque and surface EMG from the quadriceps and hamstring muscle groups were collected and quantified in a window between 30 and 70 degrees knee angle (range of motion 90-5 degrees ) during maximal voluntary eccentric and concentric knee extensor actions at 30, 90, and 270 degrees.s(-1). Changes in strength of the trained legs revealed more signs of specificity related to velocity and contraction type after eccentric than concentric training. No major training effects were present in eccentric to concentric ratios of agonist EMG or in relative antagonist (hamstring) activation. Thus, for the trained leg, the muscle action type and speed specific changes in maximal voluntary eccentric strength could not be related to any effects on neural mechanisms, such as a selective increase in muscle activation during eccentric actions. Interestingly, with both types of training there were specific cross-education effects, that is, action type and velocity specific increases in strength occurred in the contralateral, untrained, leg, accompanied by a specific increase in eccentric to concentric EMG ratio after eccentric training.     

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.     

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.     

Acute effects of static and dynamic stretching on leg flexor and extensor isokinetic strength in elite women athletes

The aim of this study was to explore the effects of static and dynamic stretching of the leg flexors and extensors on concentric and eccentric peak torque (PT) and electromyography (EMG) amplitude of the leg extensors and flexors in women athletes. Ten elite women athletes completed the following intervention protocol in a randomized order on separate days: (a) non‐stretching (control), (b) static stretching, and (c) dynamic stretching. Stretched muscles were the quadriceps and hamstring muscles. Before and after the stretching or control intervention, concentric and eccentric isokinetic PT and EMG activity of the leg extensors and flexors were measured at 60 and 180°/s. Concentric and eccentric quadriceps and hamstring muscle strength at both test speeds displayed a significant decrease following static stretching (P<0.01–0.001). In contrast, a significant increase was observed after dynamic stretching for these strength parameters (P<0.05–0.001). Parallel to this, normalized EMG amplitude parameters exhibited significant decreases following static (P<0.05–0.001) and significant increases following dynamic stretching (P<0.05–0.001) during quadriceps and hamstring muscle actions at both concentric and eccentric testing modes. Our findings suggest that dynamic stretching, as opposed to static or no stretching, may be an effective technique for enhancing muscle performance during the pre‐competition warm‐up routine in elite women athletes.