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The present study compared the ipsilateral repeated bout effect (IL‐RBE) and contralateral repeated bout effect (CL‐RBE) of the elbow flexors (EF) and knee flexors (KF) for the same interval between bouts to shed light on their mechanisms. Fifty‐two healthy sedentary young (20–28 years) men were randomly assigned to the IL‐EF, IL‐KF, CL‐EF, and CL‐KF groups (n = 13/group). Thirty maximal eccentric contractions of the EF were performed in IL‐EF and CL‐EF, and 60 maximal eccentric contractions of the KF were performed in IL‐KF and CL‐KF, with a 2‐week interval between bouts. Changes in muscle damage markers such as maximal voluntary contraction (MVC) torque, muscle soreness, and plasma creatine kinase activity, and proprioception measures before to 5 days post‐exercise were compared between groups. Changes in all variables were greater (p < 0.05) after the first than second bout for all groups, and the changes were greater (p < 0.05) for the EF than KF. The changes in all variables after the second bout were greater (p < 0.05) for the CL than IL condition for both EF and KF. The magnitude of the average protective effect was similar between CL‐EF (33%) and CL‐KF (32%), but slightly greater (p < 0.05) for IL‐EF (67%) than IL‐KF (61%). These demonstrate that the magnitude of CL‐RBE relative to IL‐RBE was similar between the EF and KF (approximately 50%), regardless of the greater muscle damage for the EF than KF. It appears that the CL‐RBE is more associated with neural adaptations at cerebrum, cerebellum, interhemispheric inhibition, and coricospinal tract, but the IL‐RBE is induced by additional adaptations at muscles. [ABSTRACT FROM AUTHOR]

The Nordic hamstring exercise (NHE) reduces hamstring injury incidence. Compliance to large exercise volumes of the NHE is poor, with exercise related soreness often seen as a contributing factor. We investigated the dose–response of NHE exposure with delayed onset muscle soreness (DOMS) and non‐DOMS pain. Forty males were randomized to a 6‐week intervention of four different NHE dosages: Group 1: very low volume; Group 2: low volume; Group 3: initial high to low volume; Group 4: low to high volume. Group 4 experienced more DOMS (p < 0.05) and non‐DOMS pain (p = 0.030) than other groups. High volumes of NHE increase DOMS and non‐DOMS pain while lower volume protocols have lesser DOMS and non‐DOMS pain responses. [ABSTRACT FROM AUTHOR]

The benefits of eccentric (ECC) training on fat mass (FM) remain underexplored. We hypothesized that in obese adolescents, ECC cycling training is more efficient for decreasing whole‐body FM percentage compared to concentric (CON) performed at the same oxygen consumption (VO2). Twenty‐four adolescents aged 13.4 ± 1.3 years (BMI > 90th percentile) were randomized to ECC or CON. They performed three cyclo‐ergometer sessions per week (30 min per session) for 12 weeks: two habituation, 5 at 50% VO2peak, and 5 at 70% VO2peak. Anthropometric measurements, body composition, maximal incremental CON tests, strength tests, and blood samples were assessed pre‐ and post‐training. Whole‐body FM percentage decreased significantly after compared to pretraining in both groups, though to a larger extent in the ECC group (ECC: −10% vs CON: −4.2%, P < 0.05). Whole‐body lean mass (LM) percentage increased significantly in both groups after compared to pretraining, with a greater increase in the ECC group (ECC: 3.8% vs CON: 1.5%, P <0.05). The improvements in leg FM and LM percentages were greater in the ECC group (−6.5% and 3.0%, P = 0.01 and P < 0.01). Quadriceps isometric and isokinetic ECC strength increased significantly more in the ECC group (28.3% and 21.3%, P < 0.05). Both groups showed similar significant VO2peak improvement (ECC: 15.4% vs CON: 10.3%). The decrease in homeostasis model assessment of insulin resistance index was significant in the ECC group (−19.9%). In conclusion, although both ECC and CON cycling trainings are efficient to decrease FM, ECC induces greater FM reduction, strength gains, and insulin resistance improvements and represents an optimal modality to recommend for obese adolescents. [ABSTRACT FROM AUTHOR]

Changes in muscle fascicle mechanics have been postulated to underpin the repeated bout effect (RBE) observed following exercise‐induced muscle damage (EIMD). However, in the medial gastrocnemius (MG), mixed evidence exists on whether fascicle stretch amplitude influences the level of EIMD, thus questioning whether changes in fascicle mechanics underpin the RBE. An alternative hypothesis is that neural adaptations contribute to the RBE in this muscle. The aim of this study was to investigate the neuromechanical adaptations during and after repeated bouts of a highly controlled muscle lengthening exercise that aimed to maximize EIMD in MG. In all, 20 subjects performed two bouts of 500 active lengthening contractions (70% of maximal activation) of the triceps surae, separated by 7 days. Ultrasound constructed fascicle length‐torque (L‐T) curves of MG, surface electromyography (EMG), maximum torque production, and muscle soreness were assessed before, 2 hours and 2 days after each exercise bout. The drop in maximum torque (4%) and the increase in muscle soreness (24%) following the repeated bout were significantly less than following the initial bout (8% and 59%, respectively), indicating a RBE. However, neither shift in the L‐T curve nor changes in EMG parameters were present. Furthermore, muscle properties during the exercise were not related to the EIMD or RBE. Our results show that there are no global changes in gastrocnemius mechanical behavior or neural activation that could explain the observed RBE in this muscle. We suggest that adaptations in the non‐contractile elements of the muscle are likely to explain the RBE in the triceps surae. [ABSTRACT FROM AUTHOR]

The present study investigated the changes in contractile rate of force development ( RFD) and the neural drive following a single bout of eccentric exercise. Twenty-four subjects performed 15 × 10 maximal isokinetic eccentric knee extensor contractions. Prior to and at 24, 48, 72, 96, and 168 h during post-exercise recovery, isometric RFD (30, 50 100, and 200 ms), normalized RFD [1/6,1/2, and 2/3 of maximal voluntary contraction ( MVC)] and rate of electromyography rise ( RER; 30, 50, and 75 ms) were measured. RFD decreased by 28-42% peaking at 48 h ( P < 0.01- P < 0.001) and remained depressed at 168 h ( P < 0.05). Normalized RFD at 2/3 of MVC decreased by 22-39% ( P < 0.01), peaked at 72 h and returned to baseline at 168 h. These changes in RFD were associated with a decrease in RER at 48 h-96 h ( P < 0.05- P < 0.001). Accumulated changes (area under curve) revealed a greater relative decrease in accumulated RFD at 100 ms by −2727 ± 309 (%h; P < 0.05) and 200 ms by −3035 ± 271 (%h; P < 0.001) compared with MVC, which decreased, by −1956 ± 234 (%h). In conclusion, RFD and RER are both markedly reduced following a bout of maximal eccentric exercise. This association suggests that exercise-induced decrements in RFD can, in part, be explained decrements in neural drive. [ABSTRACT FROM AUTHOR]

Different types of exercise are characterized by the ability to induce specific physiological stimuli that might be able to induce the mobilization of progenitor cells. The aim of the current study was to investigate the mobilization of hematopoietic progenitor cells ( HPCs) and endothelial progenitor cells ( EPCs) in response to endurance, resistance, and eccentric endurance exercise and their relation to markers of muscle damage and inflammation. Healthy male subjects performed acute bouts of either endurance exercise, resistance exercise, or eccentric endurance exercise. Numbers of progenitor cells and several markers of muscle damage and inflammation were determined. Although the endurance exercise was followed by an immediate and short increase of both HPCs and EPCs, the eccentric exercise evoked a long lasting increase up to 24 h for HPCs and 48 h for EPCs ( P < 0.05). After resistance exercise, an increase of HPCs was only found 3 h after exercise ( P < 0.05). A correlation was found between mobilized progenitor cells and systemic levels of granulocyte colony-stimulating factor ( G- CSF) levels ( r = 0.54 and r = 0.51, P < 0.05) as well as for HPCs and creatine kinase levels ( r = 0.57, P < 0.05). These results suggest that mobilization of progenitor cells is related to the type of exercise and possibly mediated by G- CSF and muscle damage. [ABSTRACT FROM AUTHOR]

Contracting the knee flexor muscles immediately before a maximum voluntary contraction ( MVC) of knee extension increases the maximal force that the extensor muscles can exert. It is hypothesized that this phenomenon can be impaired by muscle fiber damage following eccentric exercise [delayed onset muscle soreness ( DOMS)]. This study investigates the effect of eccentric exercise and DOMS on knee extension MVC immediately following a reciprocal-resisted knee flexion contraction. Electromyography ( EMG) was recorded from the knee extensors and flexors of 12 healthy men during knee extension MVCs performed in a reciprocal (maximal knee extension preceded by resisted knee flexion), and nonreciprocal condition (preceded by relaxation of the knee flexors). At baseline, knee extension MVC force was greater during the reciprocal condition ( P < 0.001), whereas immediately after, 24 and 48 h after eccentric exercise, the MVC force was not different between conditions. Similarly, at baseline, the EMG amplitude of the quadriceps during the MVC was larger for the reciprocal condition ( P < 0.001). However, immediately after, 24 and 48 h postexercise the EMG amplitude was similar between conditions. In conclusion, eccentric exercise abolished the facilitation of force production for the knee extensors, which normally occurs when maximum knee extension is preceded by activation of the knee flexors. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the effects of a repeated bout of eccentric exercise on health-related parameters and muscle performance on subjects undergoing atorvastatin therapy. Twenty-eight elderly men participated in the investigation and were assigned either in a control ( n = 14) or in a statin therapy group ( n = 14). All participants performed two isokinetic eccentric exercise bouts separated by 3 weeks. Muscle damage indices, resting energy expenditure, substrate metabolism, lipid and lipoprotein profile, as well as insulin sensitivity, were evaluated before and after eccentric. No differences in muscle function were observed between the two groups either at rest or after exercise. Eccentric exercise increased resting energy expenditure, increased fat oxidation, improved lipid profile, and increased insulin resistance 2 days after both eccentric exercise bouts. However, these changes appeared to lesser extent after the second bout. No differences were observed in the responses in the health-related parameters in the control and in the statin therapy group. Eccentric exercise affected similarly the control and the atorvastatin-treated individuals. The present results indicate that atorvastatin-treated elderly individuals may participate in various physical activities, even high-intensity muscle-damaging activities, without negative impact on muscle function and adaptation. [ABSTRACT FROM AUTHOR]

The main aim of this study was to evaluate the short-term effects of daily eccentric exercises on functional pain-free hand strength in subjects with long-term lateral epicondylalgia. Forty-two subjects with lateral epicondylalgia were randomly assigned either to a 6-week home exercise regimen receiving eccentric training for their wrist extensors and a forearm band or to a control group receiving a forearm band only. The main outcomes were pain-free hand-grip and wrist-extensor strength at mid- and end-intervention follow-ups, 3 and 6 weeks after inclusion, respectively. Secondary outcomes were a change in the proportion of cases with epicondylalgia and ratings of perceived pain (VAS) at follow-up. Thirty-seven (88%) subjects completed both the mid- and the end-intervention follow-up. Exercise members had significantly higher pain-free hand-grip ( P=0.025) and wrist-extensor strength ( P<0.001) at the end of follow-up, although there was no such effect at mid-intervention. Regression analysis showed a reduction in the proportion of cases in the exercise group at the end of follow-up ( P=0.035). However, no between-groups effect emerged for perceived pain. These data suggest that the daily home eccentric exercise regimen is effective in increasing functional pain-free grip strength and reducing cases suffering from lateral epicondylalgia. However, no effect emerged for global perceived pain during the last week. [ABSTRACT FROM AUTHOR]

Non-steroidal anti-inflammatory drugs ( NSAIDs) are widely consumed among athletes worldwide in relation to muscle injury and soreness. This review aims to provide an overview of studies investigating their effects on skeletal muscle, in particular the repair processes in injured muscle. Muscle injury occurs in diverse situations and the nature of muscle injuries varies significantly, complicating extrapolations between experimental models and 'real life.' Classical muscle strain injuries occur at the interphase between the muscle fibers and connective tissue, most often in the myotendinuous junction, whereas contusion or overload injury can damage both myofibers and intramuscular connective tissue. The role of NSAIDs in muscle repair is complicated by differences in injury models used, variables evaluated, and time point(s) selected for evaluations. While the temporal pattern of the influence of NSAIDs on muscle repair is difficult to settle on, it appears that a potential beneficial effect of NSAIDs in the early phase after injury is not maintained in the long term, or is even negated by a long-term repair deficit. At the cellular level, evidence exists for a negative influence of NSAIDs on the muscle stem cell population (satellite cells). At a structural level, it is known that muscle connective tissue undergoes significant remodeling during muscle regeneration, but the potential of NSAID exposure to alter this response in humans needs investigation. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effects of whole-body cryotherapy (WBC) on proprioceptive function, muscle force recovery following eccentric muscle contractions and tympanic temperature ( TTY). Thirty-six subjects were randomly assigned to a group receiving two 3-min treatments of −110 ± 3 °C or 15 ± 3 °C. Knee joint position sense (JPS), maximal voluntary isometric contraction (MVIC) of the knee extensors, force proprioception and TTY were recorded before, immediately after the exposure and again 15 min later. A convenience sample of 18 subjects also underwent an eccentric exercise protocol on their contralateral left leg 24 h before exposure. MVIC (left knee), peak power output (PPO) during a repeated sprint on a cycle ergometer and muscles soreness were measured pre-, 24, 48 and 72 h post-treatment. WBC reduced TTY, by 0.3 °C, when compared with the control group ( P<0.001). However, JPS, MVIC or force proprioception was not affected. Similarly, WBC did not effect MVIC, PPO or muscle soreness following eccentric exercise. WBC, administered 24 h after eccentric exercise, is ineffective in alleviating muscle soreness or enhancing muscle force recovery. The results of this study also indicate no increased risk of proprioceptive-related injury following WBC. [ABSTRACT FROM AUTHOR]

To examine the effects of eccentric exercise (EE) and ischemia/reperfusion (I/R) on the markers of muscle damage, 72 rats were randomly assigned to the EE group, I/R group and control group (C), respectively. The rats in EE ran downhill on a treadmill with a 16° inclination at a constant speed for 90 min, and the rats in the I/R group underwent 90 min of four-limb ischemia, followed by 24, 48 and 72 h of reperfusion. Blood and tissue samples were collected immediately, 24, 48 and 72 h after exercise or reperfusion. Quantitative analyses showed that the I/R group had a significantly larger mitochondrial volume at 24 h after reperfusion compared with the C, and there were more disrupted Z-lines in the EE group and more disrupted mitochondria in the I/R group at 24 h after exercise or reperfusion. When compared with the C, a significantly lower total antioxidant capacity and higher interleukin-6 value were observed after exercise or reperfusion. Our data suggest that although EE and I/R result in some similar changes in the muscle damage markers, there are still some differences. The EE- and I/R-induced muscle damage may be due to different mechanisms. [ABSTRACT FROM AUTHOR]

Recovery from micro damage resulting from intensive exercise has been shown to take longer in older muscles. To investigate the factors that may contribute to muscle repair, we have studied the expression of two splice variants of the insulin-like growth factor-I (IGF-I) gene. IGF-IEa and mechano growth factor (MGF) were studied in response to 1 h of eccentric cycling exercise in young and old individuals. Subjects (nine young, aged 20–27 years and eight elderly, aged 67–75 years) completed an eccentric exercise protocol that consisted of 60 min of reverse pedal cycling. Workloads were chosen to give the same relative increases in oxygen uptake (VO2max) and heart rate in young and old subjects. Muscle biopsy samples were obtained from the quadriceps muscle before and 2¼ h after completion of the exercise bout and were analyzed for IGF-IEa and MGF mRNA levels using real-time quantitative PCR. No difference was observed between the baseline levels of the two splice variants between the two subject groups. Eccentric cycling exercise resulted in a significant increase in the mean MGF mRNA in both young and old subjects but did not alter IGF-IEa mRNA levels in either age group. As reported previously ( Toft et al., 2002 ), the levels of serum creatine kinase and myoglobin, markers of muscle damage, were increased significantly from baseline and to 5 days after exercise in both young and old subjects. This supports previous research in suggesting that the MGF splice variant is sensitive to muscle damage-inducing exercise and is differentially regulated compared with IGF-IEa. [ABSTRACT FROM AUTHOR]

Eccentric exercise affects muscles differentially according to intensity, duration, and previous exposure to the specific exercise activity. We used T2-weighted magnetic resonance imaging sequences to localize and quantify muscle damage following step exercise and to determine correlations between transverse relaxation time (T2) and other markers of muscle damage. Eight women performed two-step exercise bouts (30 min) separated by 8 weeks. Blood samples, MR scans, measurements of muscle strength, and muscle soreness were obtained immediately before, after, and up to 9 days after each bout. Resting muscle T2 (40.3±0.6 ms) increased exclusively in m. Adductor magnus (AM) in the thigh performing eccentric contractions and peaked 3 days after bout 1 (73.5±9.7 ms, P<0.05). Plasma creatine kinase (CK) activity peaked on day 3 after bout 1 and correlated with T2 in AM ( r=0.96, P<0.001). After bout 2 CK and T2 were almost unaffected. This indicates that T2-weighted MRI can be applied to identify muscles from which enzymes are being released into the circulation. [ABSTRACT FROM AUTHOR]

Background: Intratendinous Doppler activity has been interpreted as an equivalent of neovessels in the Achilles tendon and as a sign of tendinosis (AT). Aim: To evaluate the vascular response as indicated by color Doppler activity after repeated loading of both symptomatic and non-symptomatic Achilles tendons. Material and methods: Ten non-trained, healthy subjects ran 5 km. Ultrasound (US) Doppler activity was determined before and after the exercise. Eleven patients with chronic AT performed 3 × 15 heavy-load eccentric exercise. The Achilles tendons were scanned before and immediately after the exercise. Results: Non-symptomatic: six Achilles tendons in five subjects had intratendinous Doppler activity before the exercise. All but two subjects (80%) had intratendinous Doppler activity after running. Symptomatic: all patients had Doppler activity in the tendons, with a median color fraction before eccentric exercise of 0.05 (range 0.01–0.33). The Doppler activity did not disappear after exercise. Tendons with a color fraction below the median at baseline increased significantly after the exercise ( P=0.02). Conclusion: The mere presence of Doppler in the Achilles tendon does not per se indicate disease. Eccentric exercise does not extinguish the flow during or after one training session in patients with chronic AT. [ABSTRACT FROM AUTHOR]

The purpose of this investigation was to, firstly, examine the effects of repeated applications of ice massage on the indirect markers associated with muscle damage using a within-subjects cross-over design and secondly, to examine how ice massage affects muscle function in both static and dynamic contractions following unaccustomed eccentric exercise. Twelve males performed damaging exercise on two separate occasions. The protocol consisted of three sets of 10 maximal eccentric repetitions of the elbow flexors using isokinetic dynamometry. Subjects were randomly assigned to an ice massage group or placebo group and received treatments immediately post-exercise, 24 and 48 h post-exercise. Muscle function (maximal isometric, slow and fast isokinetic contractions), creatine kinase, myoglobin, muscle soreness, limb girth and range of motion were measured pre, immediately post, 24, 48, 72 and 96 h post-exercise. Significant time effects were observed for all dependent variables ( P<0.05). There were no significant differences between treatments. Ice massage is ineffective in reducing the indirect markers associated with exercise-induced muscle damage and enhancing recovery of muscle function in male exercisers unaccustomed to eccentric biased exercise. [ABSTRACT FROM AUTHOR]

The biomechanical and regenerative responses in rabbit tibialis anterior muscle following a single eccentric stretch injury were investigated 1, 3 and 7 days after traumatization. The stretch injury produced a transient biomechanical effect. On day 1, the load at failure was decreased in the injured muscles compared with the uninjured controls (P<0.05), but on days 3 and 7 significant biomechanical differences were no longer recorded between the injured and control muscles. In immunohistochemical analyses, no overt myonecrosis or connective tissue disruption was observed in any of the stretch-injured muscles. Yet satellite cells were activated to incorporate a thymidine analogue, bromodeoxyuridine indicating mitotic activity. They did not, however, produce muscle-specific proteins, i.e., they did not differentiate further. Furthermore, the intact appearing but mildly injured myofibers of the stretched muscles expressed both neonatal myosin and vimentin near the myotendinous junctions. Collectively, these results suggest that a single mild eccentric stretch of skeletal muscle which does not cause gross structural alterations results in a short-term decrease in tensile load and induces transient proliferation of satellite cells and fibroblasts together with expression of primitive proteins in myofibers. [ABSTRACT FROM AUTHOR]