Responses of old men to repeated bouts of eccentric exercise of the elbow flexors in comparison with young men

A bout of eccentric exercise confers protection against subsequent bouts of the same exercise. This study investigated whether the protective effect would be produced similarly between old and young adults. Eight old men (70.5 ± 4.1 years) and ten young men (20.4 ± 2.0 years) performed two bouts of eccentric exercise of the elbow flexors (six sets of five eccentric actions) separated by 4 weeks. Changes in maximal isometric strength, range of motion (ROM), upper arm circumference (CIR), plasma creatine kinase (CK) activity, myoglobin (Mb) concentration, and muscle soreness (SOR) before, immediately after, and 1, 24, 48, 72 and 96 h following exercise were compared between bouts, and between groups by a two-way repeated measures ANOVA. Changes in the measures following the first bout were significantly (P < 0.05) smaller for the old than the young group. The young group showed significantly (P < 0.05) smaller changes in all measures following the second bout than the first bout; however, the old group had the protective effect only for ROM, Mb, and SOR. The magnitude of the effect observed for ROM and Mb concentration in the old group was significantly (P < 0.05) smaller compared with that of the young group. These results suggest that the protective effect conferred by the first bout was less for the old than the young group. This may be due to the less muscle damage after the first bout in the old subjects, but it is also possible that the protective effect of old adults does not last as long as that of young adults.     

Effect of eccentric exercise on plasma enzyme activities previously elevated by eccentric exercise

The purpose of this study was to investigate whether plasma activities of creatine kinase (CK) and glutamic-oxaloacetic transaminase (GOT), elevated by eccentric exercise, would be affected by a second bout of eccentric exercise. A group of 26 male students [20.3 (SD 1.9) years] were placed in one of three groups. Group A (n = 8) performed one bout of 24 maximal eccentric actions (ECC) of the forearm flexors (ECC1), and groups B (n = 10) and C (n = 8) performed two bouts of ECC (ECC1, ECC2). The ECC2 was performed by the opposite arm 3 days (group B) or 5 days (group C) after ECC1. None of the subjects had performed this eccentric exercise prior to this study. Maximal isometric force (MIF), range of motion (ROM), upperarm circumference (CIR), muscle soreness level (SOR), and plasma CK and GOT activities were measured before and for 8 days (group B) or 10 days (groups A, C) postexercise. The MIF, ROM, CIR, and SOR changed significantly after exercise (P<0.01), and no significant differences in changes were found between ECC1 and ECC2, or among the groups. This suggested that ECC1 and ECC2 produced a similar stress to the forearm flexor muscles. Therefore, it was expected that CK and GOT activities would show similar increases after ECC1 and ECC2. However, increases in CK and GOT activities after ECC2 were significantly smaller (P<0.01) than after ECC1 in both groups B and C. The results of this study confirmed that CK and GOT responses were diminished when initial blood enzyme activities were elevated.     

Muscle damage responses of the elbow flexors to four maximal eccentric exercise bouts performed every 4 weeks

Since little is known about the repeated bout effect of more than two eccentric exercise bouts, this study compared muscle damage responses among four exercise bouts. Fifteen young (21.8 ± 1.9 years) men performed four bouts of 30 maximal isokinetic eccentric contractions of the elbow flexors every 4 weeks. Maximal voluntary elbow flexion isometric and concentric strength, range of motion at the elbow joint (ROM), upper arm circumference, blood markers of muscle damage, and muscle soreness were measured before and up to 120 h following each bout. Changes in all measures following the second to fourth bouts were significantly (P < 0.05) smaller than those after the first bout. The decreases in strength and ROM immediately after the fourth bout were significantly (P < 0.05) smaller than other bouts. It is concluded that the first bout confers the greatest adaptation, but further adaptation is induced when the exercise is repeated more than three times.     

Effects of eccentric exercise-induced muscle injury on blood levels of platelet activating factor (PAF) and other inflammatory markers

It has been reported that exercise with eccentric contractions can induce damage and inflammation in human muscle tissue, the severity of which depends on the duration and the intensity of exercise. Platelet activating factor (PAF) is a potent inflammatory mediator implicated in a series of pathophysiological conditions. We sought to investigate the relationship between PAF and eccentric exercise induced muscle damage. Thirteen healthy, recreationally active male subjects (27.5±3.78 year) performed 36 maximum voluntary eccentric contractions on a motorized muscle dynamometer using the elbow flexor muscles of the non-dominant arm. Venous blood samples were collected immediately before and after exercise at 2, 24, 48, 72 and 96 h. PAF was isolated, purified and determined by a platelet aggregation assay. Serum levels of creatine kinase (CK), lactate dehydrogenase (LDH), C-reactive protein (CRP) and complement C3 (C3), plasma level of fibrinogen and whole blood level of leukocytes (and their subsets) were determined. Established indicators of muscle damage as maximum isometric torque (MIT), range of motion (ROM), relaxed arm angle (RANG), flexed arm angle (FANG), arm circumference (CIRC) and muscle soreness were also measured at the same time points. PAF, leukocytes, CK and LDH were elevated after exercise, while other biochemical parameters such as CRP, C3 and fibrinogen were unchanged. We also observed an inverse association between PAF and MIT and ROM, as well as a positive association with other markers of muscle injury, i.e. CK, LDH, FANG and CIRC (all P’s<0.05). Our findings may imply a role for PAF in the mechanism of eccentric exercise induced muscle damage.     

Changes in the angle-force curve of human elbow flexors following eccentric and isometric exercise

The aim of this study was to explore and compare the magnitude and time-course of the shift in the angle-force curves obtained from maximal voluntary contractions of the elbow flexors, both before and 4 consecutive days after eccentric and isometric exercise. The maximal isometric force of the elbow flexors of fourteen young male volunteers was measured at five different elbow angles between 50° and 160°. Subjects were then divided into two groups: the eccentric group (ECC, n=7) and the isometric group (ISO, n=7). Subjects in the ECC group performed 50 maximal voluntary eccentric contractions of the elbow flexors on an isokinetic dynamometer (30°^.s^–1), while subjects in the ISO group performed 50 maximal voluntary isometric muscle contractions with the elbow flexors at a lengthened position. Following the ECC and ISO exercise protocols, maximal isometric force at the five angles, muscle soreness, and the relaxed (RANG) and flexed (FANG) elbow angles were measured at 24 h intervals for 4 days. All results were presented as the mean and standard error, and a quadratic curve was used to model the maximal isometric force data obtained at the five elbow angles. This approach not only allowed us to mathematically describe the angle-force curves and estimate the peak force and optimum angle for peak force generation, but also enabled us to statistically compare the shift of the angle-force curves between and within groups. A large and persistent shift of the angle-force curve towards longer muscle lengths was observed 1 day after eccentric exercise (P<0.01). This resulted in a ~16° shift of the optimum angle for force generation, which remained unchanged for the whole observation period. A smaller but also persistent shift of the angle-force curve was seen after isometric exercise at long muscle length (P<0.05; shift in optimum angle ~5°). ECC exercise caused more muscle damage than ISO exercise, as indicated by the greater changes in RANG and ratings of muscle soreness (P<0.05). It was suggested that the shift in the angle-force curve was proportional to the degree of muscle damage and may be explained by the presence of overstretched sarcomeres that increased in series compliance of the muscle.     

Changes in hardness of the human elbow flexor muscles after eccentric exercise

The purpose of this study was to investigate changes in muscle hardness after eccentric exercise of the elbow flexors muscles that produce muscle shortening and swelling. To assess muscle hardness, a pressure method was used in which the force required to deform the tissue (skin, subcutaneous tissue, muscle) was recorded. Eleven healthy male students performed 24 maximal eccentric actions of the elbow flexor muscles with their non-dominant arms. Muscle hardness, maximal isometric force (MIF), muscle soreness, plasma creatine kinase (CK) activity, relaxed elbow joint angle (RANG), upper-arm circumference (CIR) and B-mode ultrasound transverse images were measured before, immediately after, and 1–5 days after exercise. A long-lasting decrease in MIF, muscle swelling shown by increases in CIR and muscle thickness, large increases in plasma CK activity, and development of muscle soreness indicated that damage occurred to the elbow flexor muscles. The RANG had decreased by approximately 20° at 1–3 days after exercise and showed a gradual recovery thereafter. The CIR increased gradually after exercise and peaked on day 5 post-exercise, the mean amount of increase in CIR being 18 mm. Muscle hardness measured at the relaxed elbow position did not change until 3 days after exercise, but increased significantly (P < 0.01) on days 4 and 5 post-exercise. On the other hand, muscle hardness measured when forcibly extending the shortened elbow joint increased significantly (P < 0.01) with time and peaked at 3 days after exercise. Muscle hardness assessed by the pressure method seems to reflect changes in muscle stiffness and swelling. Accepted: 15 April 2000     

The repeated bout effect of reduced-load eccentric exercise on elbow flexor muscle damage

In this study we investigated the extent to which an initial eccentric exercise consisting of two (2ECC) or six maximal eccentric actions (6ECC) of the elbow flexors would produce a similar effect to 24 maximal eccentric actions (24ECC), on a second bout of 24ECC performed 2 weeks later. Male students (n=34) were assigned to one of three groups, and with their non-dominant arm performed either 2ECC (n=12), 6ECC (n=10), or 24ECC (n=12) as a first bout of exercise. Two weeks later all groups performed 24ECC. Maximal isometric strength, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase activity and myoglobin concentration were assessed before, immediately after, and for 4 days after exercise. Changes in all variables were compared between the bouts and groups by a two-way repeated measures analysis of variance. All variables changed significantly (P<0.05) after 2ECC, 6ECC, and 24ECC, but the amount of change after 2ECC and 6ECC was significantly smaller (P<0.05) than both 6ECC and 24ECC, and 24ECC, respectively. After the second bout, the 6ECC and 24ECC groups showed a profound repeated bout effect, and no significant differences were found between the groups. All variables except muscle soreness were significantly (P<0.05) larger after the second bout for the 2ECC group, however the changes observed after 24ECC were significantly smaller (P<0.01) than those observed after the first 24ECC of the 24ECC group. These results suggest that it is not necessary to conduct a high number of eccentric actions in the first bout to elicit a repeated bout effect in a subsequent bout performed some time later. Electronic Publication     

Muscle adaptation prior to recovery following eccentric exercise

Summary The effects of performing a second eccentric exercise bout prior to and after recovery from the first bout were compared. Twenty subjects performed 70 eccentric actions with the forearm flexors. Group A (n = 9) and group B (n = 11) repeated the same exercise 5 and 14 days after the initial bout, respectively. Dependent variables included muscle soreness, elbow joint angles, isometric strength, and serum creatine kinase (SCK). Subjects were tested pre-exercise and up to day 5 following each bout. The first bout produced significant changes in all measures for both groups (P < 0.01). Values remained significantly different from baseline on day 5 when group A repeated the exercise (P < 0.01) but were back to normal when group B performed bout 2. For both groups an adaptation occurred; significantly smaller changes in dependent variables were produced by the second bout, and recovery time was faster whether or not muscles were fully restored (P < 0.01). The repeated bout did not exacerbate soreness, performance decrements, and elevation of SCK when performed by affected muscles that had not fully recovered from the first bout. Thus, the results suggest that an adaptation response had taken place prior to full recovery and restoration of muscle function following the initial eccentric exercise bout.     

Indices of free-radical-mediated damage following maximum voluntary eccentric and concentric muscular work

This study monitored plasma and skeletal muscle markers of free-radical-mediated damage following maximum eccentric and concentric exercise, to examine the potential role of free radicals in exercise-induced muscle damage. Fourteen male volunteers performed either (1) a bout of 70 maximum eccentric and a bout of 70 maximum concentric muscle actions of the forearm flexors (the bouts being separated by 4 weeks; n = 8) or (2) a bout of 80 maximum eccentric and a bout of 80 maximum concentric muscle actions of the knee extensors (the bouts being separated by 1 week; n=6). Plasma markers of lipid peroxidation, thiobarbituric acid-reactive substances (TBARS) and diene-conjugated compounds (DCC) were monitored in the arm protocol and skeletal muscle markers of oxidative lipid and protein damage, malondialdehyde (MDA) and protein carbonyl derivatives (PCD) respectively, were monitored in the leg protocol. In both protocols, the contralateral limb was used for the second bout and the order of the bouts was randomised between limbs. Repeated measures ANOVA indicated significant changes from baseline following eccentric arm work on the measures of serum creatine kinase activity (P < 0.05), maximum voluntary torque production (P < 0.01) and relaxed arm angle (P < 0.01). Subjective muscle soreness peaked 2 days after eccentric arm work (P < 0.05, Wilcoxon test). However, there were no changes in the plasma levels of TBARS or DCC following the eccentric or concentric arm exercise. Immediately after concentric leg exercise, skeletal muscle PCD concentrations was significantly higher than that observed immediately after eccentric work (P < 0.05). However, no significant difference between the eccentric and concentric knee extensor bouts was observed on the measure of skeletal muscle MDA concentration. The results of this study offer no support for the involvement of oxygen free radicals in exercise-induced muscle damage.     

Attenuation of protective effect against eccentric exercise-induced muscle damage.

A single bout of eccentric exercise confers a long-lasting protective effect against subsequent bouts of the same exercise. This study investigated how the protective effect was lessened when the interval between the initial and secondary exercise bouts was increased from 4 to 12 weeks. Thirty young men performed two bouts of 12 maximal eccentric actions of the elbow flexors of the nondominant arm separated by either 4 (n = 9), 8 (n = 10), or 12 (n = 11) weeks. Maximal isometric strength, flexed and relaxed elbow joint angles, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase (CK), and myoglobin (Mb) were measured before, immediately after, and for 4 days after exercise. Changes in criterion measures were compared between bouts for each group and among groups by two-way repeated-measures ANOVA. There were no significant differences among groups in the changes in all measures following the first bout. Significantly (p < 0.05) smaller responses in all measures were observed after the second bout as compared with first bout for the 4 and 8 weeks, but only in strength, muscle soreness, CK, and Mb for the 12 weeks. It was concluded that some aspects of the protective effect were attenuated after 8 weeks, and the factors responsible for the effect vary among the measures.     

The repeated bout effect and heat shock proteins: intramuscular HSP27 and HSP70 expression following two bouts of eccentric exercise in humans

Exercise-induced damage significantly and predictably alters indirect indicators of muscle damage after one bout of damaging exercise but this response is dampened following a second bout of the same exercise performed 1-6 weeks later. Previously we have described a marked increase in the levels of heat shock proteins (HSPs) HSP27 and HSP70 in human biceps muscle following one bout of high-force eccentric exercise. The purpose of the present study was to examine the intramuscular HSP27 and HSP70 response following two identical bouts of exercise [bout 1 (B1) and bout 2 (B2), separated by 4 weeks] relative to indirect indices of muscle damage. Ten human subjects performed 50 high-force eccentric contractions with their non-dominant forearm flexors; muscle damage of the biceps brachii was evaluated 48 h post-exercise with indirect indices [serum creatine kinase (CK) activity, soreness, isometric maximal voluntary contraction (MVC) force and relaxed arm angle] and immunoblotting of high ionic strength muscle biopsy extracts for both HSPs. Not unexpectedly, the indirect indicators of damage changed dramatically and significantly (P < 0.01) after B1 but had a much smaller response after B2. The magnitude of the HSP response was the same after both bouts of exercise, though the control and exercised samples of B2 demonstrated a lower basal HSP expression. Thus, though both indirect and cellular indicators of exercise-induced muscle damage demonstrate an adaptation consequent to the first bout of exercise, these adaptations are quite different. It is possible that the lower basal HSP expression of the cellular response mediates the attenuation of damage associated with B2 as indicated by indirect indices.     

Changes in fluctuation of isometric force following eccentric and concentric exercise of the elbow flexors

This study tested the hypothesis that eccentric exercise (ECC) would increase force fluctuation for several days following exercise; however, concentric exercise (CON) would not produce such an effect. Twelve men performed six sets of five reps of dumbbell exercise of the elbow flexors eccentrically with one arm and concentrically with the other, separated by 4–6 weeks, using a dumbbell set at 50% of maximal voluntary isometric contraction (MVC) measured at 90° of elbow flexion. MVC, range of motion (ROM), upper arm circumference, plasma creatine kinase activity (CK), myoglobin concentration (Mb) and muscle soreness were assessed before, immediately after, 1 h and 1–5 days following both exercise bouts. Force fluctuations during 30, 50 and 80% MVC were quantified by coefficient of variation (CV) of the force data (sampling frequency: 100 Hz) for 4 s. Significantly (P<0.01) larger changes in MVC, ROM, and upper arm circumference were evident following ECC compared to CON, and only ECC resulted in significant (P<0.01) increases in CK and Mb, and development of muscle soreness. Significant (P<0.01) differences existed between ECC and CON for changes in force fluctuations. CV increased significantly (P<0.01) immediately and 1 h after ECC from baseline for 30, 50, and 80% MVC without a significant difference among the intensities, and no significant changes in CV were evident following CON. It was concluded that increases in force fluctuation were peculiar to ECC, but did not necessarily reflect muscle damage.     

Less indication of muscle damage in the second than initial electrical muscle stimulation bout consisting of isometric contractions of the knee extensors

This study compared the first and second exercise bouts consisting of electrically evoked isometric contractions for muscle damage profile. Nine healthy men (31 ± 4 years) had two electrical muscle stimulation (EMS) bouts separated by 2 weeks. The knee extensors of one leg were stimulated by biphasic rectangular pulses (75 Hz, 400 μs, on–off ratio 5–15 s) at the knee joint angle of 100° (0°, full extension) to induce 40 isometric contractions, while the current amplitude was increased to maintain maximal force generation. Maximal voluntary isometric contraction (MVC) torque of the knee extensors at 100°, muscle soreness, pressure pain threshold and plasma creatine kinase (CK) activity were used as indirect markers of muscle damage, and measured before and 1, 24, 48, 72 and 96 h after EMS bout, and the changes over time were compared between bouts. The torque produced during exercise was approximately 30% of MVC, and no significant difference between bouts was evident for the changes in peak and average torque over 40 contractions. MVC decreased significantly (P < 0.05) by 26% immediately and 1 h after both bouts, but the recovery was significantly (P < 0.05) faster after the second bout (100% at 96 h) compared with the first bout (81% at 96 h). Development of muscle soreness and tenderness, and increases in plasma CK activity were significantly (P < 0.05) smaller after the second than the first bout. These results show that changes in muscle damage markers were attenuated in the second EMS bout compared with the initial EMS bout.     

Responses of human elbow flexor muscles to electrically stimulated forced lengthening exercise

This study developed an electrical stimulation model for human elbow flexors to examine eccentric exercise-induced muscle damage and adaptation. Male students (n=17) were randomly placed into one of two groups; isometric (ES-ISO, n=8) and eccentric (ES-ECC, n=9). The elbow joint was fixed at 90 degrees (1.57 rad) and the elbow flexors stimulated percutaneously by an electronic muscle stimulator for 5 s through two electrodes placed over the muscles for ES-ISO. In ES-ECC, the muscles were stimulated similarly to the ES-ISO, but the elbow joint was forcibly extended from an elbow flexed (90 degrees 1.57 rad) to a full-extended position (180 degrees, 3.14 rad) in 3 s. Maximal voluntary isometric force, range of motion, upper arm circumference, muscle thickness by ultrasonography, muscle soreness, plasma creatine kinase and aspartate aminotransferase activities were assessed before and for 4 days after exercise. ES-ECC produced significantly larger changes in all criterion measures compared with ES-ISO (P < 0.01). These findings confirmed that eccentric muscle actions induced muscle damage, but isometric contractions resulted in little or no damage. Six subjects from the ES-ECC group repeated the same eccentric exercise (ECC2) 2 weeks after the first bout (ECC1), and changes in the criterion measures were compared between the bouts. Changes in all criterion measures after ECC2 were significantly smaller than ECC1 (P < 0.01). These results suggest that the first eccentric exercise produced a protective effect against muscle damage in the subsequent eccentric exercise bout, which does not involve adaptations in the central nervous system.     

Effects of a second bout of maximal eccentric exercise on muscle damage and electromyographic activity

This study examined whether a second bout of maximal eccentric exercise performed 3 days after the first exercise bout would produce further changes in muscle damage and electromyographic activity (EMG). Male students (n=26) were randomly assigned to experimental 70 (EX70; n=9), experimental 30 (EX30; n=8), and control (CON; n=9) groups. The initial exercise was 30 maximal voluntary isokinetic eccentric contractions (MAX1) on non-dominant elbow flexors at 60° s⁻¹ (1.05 rad s^-1). The EX70 and EX30 groups performed a second bout of 70 and 30 eccentric contractions (MAX2), respectively, 3 days after MAX1. Upper arm circumference , range of motion , strength, integrated EMG (IEMG), and mean power frequency (MPF) were measured before, immediately after, and once a day for 9 days after MAX1. Plasma creatine kinase (CK) activity and muscle soreness were assessed before and for 9 days after MAX1. Total work, work per contraction, IEMG, and MPF were also recorded during MAX1 and MAX2. All indicators of muscle damage changed following MAX1 for each group (P<0.05), but no indicators of additional damage (P>0.05) were apparent after MAX2 for either the EX70 or EX30 groups. IEMG (P=0.03) and MPF (P=0.04) were lower for MAX2 compared with MAX1 for both the EX30 and EX70 groups. It is concluded that performing a second bout of eccentric exercise with damaged muscles 3 days after the initial bout does not produce further damage or retard recovery, even when the second bout of exercise is more strenuous. EMG findings were consistent with reduced activation of fast-twitch motor units during the second eccentric bout. These results may be interpreted as evidence of a neural protective mechanism. Electronic Publication     

The influence of cold water immersions on adaptation following a single bout of damaging exercise

The aim of this investigation was to elucidate the effects of cold water immersions (CWIs) following damaging exercise on the repeated bout effect (RBE). Sixteen males performed two bouts of drop jump exercise separated by 14–21 days. Participants were equally, but randomly assigned to either a CWI (12-min CWI at 15°C) or control group (12-min seated rest). Treatments were given immediately after the first exercise bout, 24, 48 and 72 h post-exercise. No interventions were given following the second bout. Maximum voluntary contraction (MIVC), soreness (DOMS), creatine kinase (CK), thigh girth and range of motion (ROM) were recorded before and for 96 h following the initial and repeated bouts of damaging exercise. All variables, except ROM, showed a significant time effect (P < 0.01) indicating the presence of muscle damage following the initial bout; there were no differences between the CWI and control groups after the initial bout. Following the repeated bout of exercise there was a significant attenuation in the reduction of MIVC (P = 0.002) and a reduction in DOMS (P < 0.001), which is indicative of the RBE. There were no significant differences between groups following the repeated bout of damaging exercise. These data show that CWI had no effect following damaging exercise and did not inhibit the RBE. Despite CWI being used routinely, its efficacy remains unclear and there is a need to elucidate the benefits of this intervention on recovery and adaptation to provide practitioners with evidence based practice.     

Effects of concentric and repeated eccentric exercise on muscle damage and calpain–calpastatin gene expression in human skeletal muscle

The purpose of this study was to compare the responsiveness of changes in Ca²⁺-content and calpain–calpastatin gene expression to concentric and eccentric single-bout and repeated exercise. An exercise group (n = 14) performed two bouts of bench-stepping exercise with 8 weeks between exercise bouts, and was compared to a control-group (n = 6). Muscle strength and soreness and plasma creatine kinase and myoglobin were measured before and during 7 days following exercise bouts. Muscle biopsies were collected from m. vastus lateralis of both legs prior to and at 3, 24 h and 7 days after exercise and quantified for muscle Ca²⁺-content and mRNA levels for calpain isoforms and calpastatin. Exercise reduced muscle strength and increased muscle soreness predominantly in the eccentric leg (P < 0.05). These responses as well as plasma levels of creatine kinase and myoglobin were all attenuated after the repeated eccentric exercise bout (P < 0.05). Total muscle Ca²⁺-content did not differ between interventions. mRNA levels for calpain 2 and calpastatin were upregulated exclusively by eccentric exercise 24 h post-exercise (P < 0.05), with no alteration in expression between bouts. Calpain 1 and calpain 3 mRNA did not change at any specific time point post-exercise for either intervention. Our mRNA results suggest a regulation on the calpain–calpastatin expression response to muscle damaging eccentric exercise, but not concentric exercise. Although a repeated bout effect was demonstrated in terms of muscle function, no immediate support was provided to suggest that regulation of expression of specific system components is involved in the repeated bout adaptation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Evidence of a contralateral repeated bout effect after maximal eccentric contractions

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

Delayed-onset muscle soreness and motor performance of the upper extremity

The purpose of this study was to examine the effects of delayed-onset muscle soreness after a strength-training session on the motor performance of the upper extremities, including the reaction time, speed of movement, tapping speed and coordination. In addition, muscle strength, electromyographic (EMG) activity, creatine kinase (CK) and soreness responses were measured. The study was a randomised cross-over intervention study, where 30 subjects (divided into two groups, A and B) performed a 1-h muscle strength-training session of the upper extremities, and the responses were measured 48 h after that. All of the subjects experienced muscle soreness, which was evaluated on a visual analogue scale. The mean value of CK activity was 115 IU·l^–1 before training and 1259 IU·l^–1 after training (P<0.001). There were no statistically significant differences in wrist flexion/extension muscle strength or EMG tests in either group. Isometric elbow extension strength decreased by 4% (P<0.01) in group A, and elbow flexion strength decreased by 6% (P<0.05) in group B. There were no statistically significant changes in simple reaction time, choice reaction time, or speed of movement or coordination in either group. However, tapping speed decreased by 2% (P<0.05) in group A and by 6% (P<0.001) in group B. Based on the results of this study, it seems that the feeling of incompetence to perform fast and accurate movements with sore muscles is mainly a subjective feeling, and it may be that the real effect of muscle soreness on motor performance is quite small, and presumably less than generally assumed. Electronic Publication     

The role of exercising muscle length in the protective adaptation to a single bout of eccentric exercise

The purpose of this study was to determine if the protective adaptation to a single bout of eccentric exercise (repeated bout effect) is dependent on the muscle length at which the eccentric contractions are performed. Ten subjects (six men, four women) performed two bouts of 120 isokinetic eccentric contractions separated by 2 weeks (target intensity was 90% of maximum isometric strength at 70°). In the initial bout one limb exercised from 30° to 70° of knee flexion (short initial bout; SIB) and the contralateral limb exercised from 70° to 110° (long initial bout; LIB). For the repeated bout 2 weeks later, the limb that initially exercised at a short length now exercised at a long length (long repeated bout; LRB) and the limb that initially exercised at a long length now exercised at a short length (short repeated bout; SRB). Isometric strength and pain (scale 0–10) were assessed immediately post exercise and on the next 3 days. Strength loss and pain were greater following LIB versus SIB (strength loss P<0.01; pain P<0.001) and following LRB versus SRB (strength loss P<0.01; pain P<0.001). Strength loss and pain were not different between LIB and LRB. Pain was significantly greater following SIB compared with SRB (P<0.05). Strength loss was not different between SIB and SRB. These results confirm that the symptoms of muscle damage are highly dependent on exercising muscle length and also demonstrate that the repeated bout effect is dependent on muscle length. Performing an initial bout of eccentric exercise at a shortened muscle length did not protect against strength loss and pain following a repeated bout at a longer muscle length. Data are given as mean (SE) unless otherwise stated.