Position sense and reaction angle after eccentric exercise: the repeated bout effect

The purpose of the present investigation was to examine the effects of a repeated eccentric exercise on position sense and muscle reaction angle. Fourteen healthy women underwent an isokinetic exercise session on their knee flexors, which was repeated after 4 weeks. Muscle damage indices, position sense and joint reaction angle of the knee were examined before, immediately after, as well as at 1, 2, 3, 4 and 7 days after exercise. The second exercise bout induced significantly lesser effects in all muscle damage indices as well as lesser disturbances in position sense and reaction angle when compared to the first one. The main finding of this study is that position sense and joint reaction angle to release of the lower limbs may adapt in response to a repeated bout of eccentric exercise, leading to less disturbances in position sense and reaction angle after the second bout of exercise.     

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.     

The repeated bout effect of eccentric exercise is not associated with changes in voluntary activation

The aim of this study was to compare the possible changes in muscle activation level between a first and second bout of damaging eccentric exercise performed at 2 weeks interval (i.e. repeated bout effect). To that purpose, ten physically active males took part in this study. The eccentric exercise consisted of 10 sets of 12 maximal voluntary contractions (MVC) produced by the knee extensors during movements performed at a constant speed of 160°s⁻¹. Changes in voluntary and electrically evoked torque in concentric and/or isometric conditions were assessed at the following time points: pre-exercise, and 2 min, 1 and 24 h after each eccentric exercise. At the same time points, voluntary activation was quantified by the superimposed electrical stimulation technique. Muscle soreness and plasma CK activity were measured within 48 h after the eccentric exercise. The results showed that the decrease in eccentric peak torque was linear throughout the exercise protocol. At the end of bouts 1 and 2, torque was significantly reduced by 27.7 ± 9.1 and 23.4 ± 11.2, respectively, with no difference between bouts (P > 0.05). At 24 h post-exercise, a lower reduction (P < 0.05) in MVC (17.8 ± 5.4%) and electrically evoked (16.7 ± 4.6%) isometric torque was observed for bout 2. In contrast, no statistical difference was found in the deficit in voluntary activation between the two bouts. In conclusion, our results indicate that the repeated bout effect of eccentric exercise appears to reduce muscle damage, but does not influence the level of voluntary activation.     

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     

Effects of set-repetition configuration in eccentric exercise on muscle damage and the repeated bout effect

The number of eccentric contractions is a factor affecting the magnitude of muscle damage; however, it is unknown whether set-repetition configurations for the same total number of eccentric contractions affect the muscle damage. The present study investigated whether different set-repetition configurations would result in different force output during eccentric exercise and different magnitude of muscle damage following the first and second exercise bouts. Ten non-resistance-trained men (26.1 ± 4.1 years) performed two bouts of eccentric exercise of the elbow flexors of each arm (4 bouts in total). One arm performed 3 sets of 10 maximal eccentric contractions (3 × 10) and the contralateral arm performed 10 sets of 3 maximal eccentric contractions (10 × 3), and each arm performed 20 sets of 3 maximal eccentric contractions (20 × 3) 4 weeks after the first bout. The order of the exercise (3 × 10, 10 × 3) and the use of arm (dominant, non-dominant) were counterbalanced amongst subjects. The torque produced over 30 eccentric contractions was similar between 3 × 10 and 10 × 3, and the changes in torque during 20 × 3 were similar between arms. Maximal voluntary contraction strength, range of motion, biceps brachii cross-sectional area and muscle soreness changed significantly (P < 0.05) following the exercise without significant differences between 3 × 10 and 10 × 3, and changes in the measures following 20 × 3 were similar between arms, except for range of motion (ROM). No significant difference in the changes in any measures except ROM was evident when compared between the first and second bouts. These results showed that changing the set-repetition configuration had little effect on muscle damage.     

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 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.     

Heat shock protein translocation and expression response is attenuated in response to repeated eccentric exercise

Aim: This study hypothesized that heat shock protein (HSP) translocation and upregulation is more probable to occur after eccentric exercise than after concentric exercise or repeated eccentric exercise. Methods: Fourteen young, healthy, untrained male subjects completed two bench‐stepping exercise bouts with 8 weeks between bouts, and were compared with a control group (n = 6). Muscle biopsies collected from m. vastus lateralis of both legs prior to and at 3 h, 24 h and 7 days after exercise were quantified for mRNA levels and/or for HSP27, αβ‐crystallin and inducible HSP70 content in cytosolic and cytoskeletal protein fractions. Results: The first bout of exercise reduced muscle strength and increased muscle soreness predominantly in the eccentric leg (P < 0.05). These responses were attenuated after the repeated eccentric exercise bout (P < 0.05), suggesting a repeated bout adaptation. Increases in inducible HSP70 and HSP27 protein content in cytoskeletal fractions were observed exclusively after eccentric exercise (P < 0.05). For HSP27, an approx. 10‐fold upregulation after first‐bout eccentric exercise was attenuated to a an approximately fourfold upregulation after the repeated eccentric exercise bout. mRNA levels for HSP70, HSP27 and αβ‐crystallin were upregulated within approximately two to fourfold ranges at time points 3 and 24 h post‐exercise (P < 0.05). This upregulation was induced exclusively by eccentric exercise but with a tendency to attenuated expression 3 h after the repeated eccentric exercise bout. Conclusion: Our results show that HSP translocation and expression responses are induced by muscle damaging exercise, and suggest that such HSP responses are closely related to the extent of muscle damage.     

Increased protein degradation after eccentric exercise

Summary The purposes of these experiments were to compare the activities of glucose 6-phosphate dehydrogenase (G6PDH) and the lysosomal enzyme N-acetyl--glucosaminidase (NAG) in rat muscles and to assess protein degradation after eccentric exercise (running down a 18 grade). The following results were obtained: (1) Muscles in which the G6PDH activity was increased also showed an increase in NAG activity that was smaller and occurred later and/or was more prolonged than the increase in G6PDH activity. (2) The urinary 3-methylhistidine/creatinine ratio was statistically elevated for 3 days after eccentric exercise and this increase was much larger and more prolonged than previously observed in rats run on the level. Taken together our results suggest that increased protein degradation after exercise is due to increased proteolysis of muscle tissue damaged during the exercise bout and that lysosomal enzymes may be involved in this degradation.     

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.     

Impact of repeated bouts of eccentric exercise on myogenic gene expression

Evidence indicates that repeated-bouts of eccentric exercise (EE) do not exacerbate the extent of muscle damage indices, as compared to a single-bout. We hypothesized that molecular adaptations, under repeated-bouts of EE, would include suppression of muscle repair inhibitory factors such as myostatin and up-regulation of muscle repair positive regulatory factors such as myogenic regulatory factors (MRFs). Fifteen males were recruited for this study. The exercise group (n = 9) successfully completed six sets of 15 reps of maximum voluntary eccentric contractions, for six consecutive days, using a dynamometer (Multicont-II). Blood and muscle biopsy samples were obtained from each subject 1 week prior to exercise, 2 days post the first training session, and 24 h after the last training session. Gene expression levels were determined using real-time RT-PCR. Blood samples were analyzed for creatine kinase (CK) and lactate-dehydrogenase (LDH) activity. Repeated-bouts of EE induced a large down-regulation of myostatin mRNA (−73%) which persisted throughout the study. The responses of MRFs were mild. At day 3 only myogenin increased significantly (1.9 fold) while MyoD decreased by 45%. Surprisingly, at day 7, despite the presence of muscle damage indices, all MRFs returned to the pre-exercise levels. The results of the present study showed that repeated-bouts of EE, for six consecutive days, dramatically decreased Myostatin mRNA expression but impaired the expression patterns of MRFs such that, with the exception of myogenin that showed a moderate non-sustained increase, MyoD and MYf5 response was minimal. Grants: Funding was provided by the Ministry of Health of the Hungarian Government. Grant number: ETT 388/2003.     

Muscle fiber conduction velocity is more affected after eccentric than concentric exercise

It has been shown that mean muscle fiber conduction velocity (CV) can be acutely impaired after eccentric exercise. However, it is not known whether this applies to other exercise modes. Therefore, the purpose of this experiment was to compare the effects of eccentric and concentric exercises on CV, and amplitude and frequency content of surface electromyography (sEMG) signals up to 24?h post-exercise. Multichannel sEMG signals were recorded from biceps brachii muscle of the exercised arm during isometric maximal voluntary contraction (MVC) and electrically evoked contractions induced by motor-point stimulation before, immediately after and 2?h after maximal eccentric (ECC group, N?=?12) and concentric (CON group, N?=?12) elbow flexor exercises. Isometric MVC decreased in CON by 21.7?±?12.0% (±SD, p?<?0.01) and by 30.0?±?17.7% (p?<?0.001) in ECC immediately post-exercise when compared to baseline. At 2?h post-exercise, ECC showed a reduction in isometric MVC by 24.7?±?13.7% (p?<?0.01) when compared to baseline, while no significant reduction (by 8.0?±?17.0%, ns) was observed in CON. Similarly, reduction in CV was observed only in ECC both during the isometric MVC (from baseline of 4.16?±?0.3 to 3.43?±?0.4?m/s, p?<?0.001) and the electrically evoked contractions (from baseline of 4.33?±?0.4 to 3.82?±?0.3?m/s, p?<?0.001). In conclusion, eccentric exercise can induce a greater and more prolonged reduction in muscle force production capability and CV than concentric exercise.     

Adaptations in biceps brachii motor unit activity after repeated bouts of eccentric exercise in elbow flexor muscles

The purpose of this study was to examine changes in motor unit activity in the biceps brachii muscle after an initial (Bout 1) and repeated (Bout 2) session of eccentric exercise separated by 1 wk. Eight subjects (aged 22 ± 2 yr) participated in experimental assessments of neuromuscular function obtained before, immediately after, 24 h after, and 7 days after each exercise bout. Each experimental session involved assessments of elbow-flexor force and biceps and triceps brachii electromyography during maximum voluntary isometric contractions (MVCs) and constant-force isometric contractions at five contraction intensities (5-50% MVC), along with indicators of muscle damage (muscle pain and passive tension). In addition, motor unit recordings were obtained before exercise, 7 days after Bout 1, and 24 h after Bout 2 to assess motor unit synchronization and recruitment thresholds. Following a single eccentric exercise session that elicited significant indicators of muscle damage, we found a 57% increase in motor unit synchronization 7 days later compared with before exercise, despite the recovery of maximal strength, soreness, and relaxed elbow-joint angle at this time. Furthermore, a second bout of the same eccentric exercise resulted in reduced indicators of muscle damage and a decline in the strength of motor unit synchronization (24 h after Bout 2) toward levels observed before both exercise sessions. In contrast, no changes in motor unit recruitment thresholds were observed 7 days after Bout 1 or 24 h after Bout 2 compared with before exercise. The increased motor unit synchronization 7 days after a single eccentric exercise session provides new evidence of changes in motor unit activity during the putative repair and regeneration phase following eccentric muscle damage.     

Expectations affect psychological and neurophysiological benefits even after a single bout of exercise

The study investigated whether typical psychological, physiological, and neurophysiological changes from a single exercise are affected by one’s beliefs and expectations. Seventy-six participants were randomly assigned to four groups and saw different multimedia presentations suggesting that the subsequent exercise (moderate 30 min cycling) would result in more or less health benefits (induced expectations). Additionally, we assessed habitual expectations reflecting previous experience and beliefs regarding exercise benefits. Participants with more positive habitual expectations consistently demonstrated both greater psychological benefits (more enjoyment, mood increase, and anxiety reduction) and greater increase of alpha-2 power, assessed with electroencephalography. Manipulating participants’ expectations also resulted in largely greater increases of alpha-2 power, but not in more psychological exercise benefits. On the physiological level, participants decreased their blood pressure after exercising, but this was independent of their expectations. These results indicate that habitual expectations in particular affect exercise-induced psychological and neurophysiological changes in a self-fulfilling manner.     

Impaired hemodynamic response to mental stress in subjects with prehypertension is improved after a single bout of maximal dynamic exercise

INTRODUCTION:

High blood pressure during mental stress in subjects with prehypertension is associated with blunted vasodilation in skeletal muscles, which might be improved by an acute bout of exercise.

OBJECTIVE:

To investigate the hemodynamic responses to mental stress before and after a bout of exercise in subjects with prehypertension.

METHOD:

Eighteen subjects with prehypertension and 16 with normotension underwent a mental stress test before and after a maximal cardiopulmonary exercise test on a treadmill. Blood pressure was measured by auscultation, and forearm blood flow was measured by venous occlusion plethysmography; from these measurements, the vascular conductance was calculated.

RESULTS:

Subjects with prehypertension had a higher mean blood pressure during mental stress (prehypertension 112±2 vs. normotension 101±3 mm Hg, p<0.05), and their vascular conductance did not increase (baseline 0.025±0.004 vs. mental stress 0.022±0.003 a.u., p>0.05). After the exercise bout, the mean blood pressure during mental stress was lower in subjects with prehypertension (before exercise 112±2 vs. after exercise 107±2 mm Hg, p<0.05), and vascular conductance increased (baseline 0.011±0.001 vs. mental stress 0.024±0.004 a.u., p<0.05).

CONCLUSION:

Subjects with prehypertension had elevated blood pressure and a blunted vasodilator response during mental stress, but their blood pressure was attenuated and their vasodilator response was normalized after a single bout of maximal dynamic exercise.     

Ventilatory and circulatory responses at the onset of exercise after eccentric exercise

The purpose of this study was to clarify whether delayed onset muscle soreness (DOMS) and muscle damage after eccentric exercise (ECC) could affect the ventilatory and circulatory responses at the onset of exercise, and whether those effects would continue after the disappearance of DOMS. Ten males participated in this study. We measured ventilatory and circulatory responses at the onset of exercise, for the first 20 s, during knee extension–relaxation voluntary exercise (VOL) and passive movement (PAS), which was achieved by the experimenter alternatively pulling ropes connected to the subjects’ ankles for the same period and frequency as during VOL. VOL and PAS were performed before, 2 days after, and 7 days after ECC. The following results were found: (1) the gain of minute ventilation at the onset of VOL at 2 days after ECC was significantly larger than that of before ECC; (2) the gain of minute ventilation at 7 days after ECC during both VOL and PAS was also enhanced significantly as compared to that of before ECC; and (3) heart rate and blood pressure responses were unchanged throughout the experimental period. In conclusion, ventilatory response at the onset of exercise is augmented during DOMS and EIMD after ECC and the enhanced ventilatory response continued after the disappearance of DOMS. It is suggested that enhanced ventilatory response during exercise after ECC is attributed to at least the changes in neural factors and that the mechanisms inducing these augmented ventilatory responses should be different during the period after ECC.     

A single bout of eccentric exercise increases HSP27 and HSC/HSP70 in human skeletal muscle

Changes in heat shock proteins (HSPs), HSP27 and HSC/HSP70 were characterized in human biceps brachii muscle following damaging high-force eccentric exercise. Male and female volunteers performed a maximal eccentric resistance exercise with the elbow flexor muscles of the non-dominant arm known to be sufficient to cause substantial muscle damage. Protein extracts of biopsy tissue samples taken 48 h post-exercise were immunoblotted for HSC/HSP70 and HSP27. Densitometric analysis demonstrated that these proteins increased significantly (P < 0.01) in the damaged biceps brachii relative to the control arm. The HSC/HSP70 increased 1064% in the exercised sample while HSP27 increased by 234%. Although the literature reports a muscular heat shock response following aerobic, oxidative exercise, this is the first documentation of increases in protein expression of both HSC/HSP70 and HSP27 in human skeletal muscle in response to a single bout of resistance exercise.