Cyclic eccentric stretching induces more damage and improved subsequent protection than stretched isometric contractions in the lower limb

PURPOSE

Controversy remains about whether exercise-induced muscle damage (EIMD) and the subsequent repeated bout effect (RBE) are caused by the stretching of an activated muscle, or the production of high force at long, but constant, muscle lengths. The aim of this study was to determine the influence of muscle fascicle stretch elicited during different muscle contraction types on the magnitude of EIMD and the RBE.

METHODS

Fourteen participants performed an initial bout of lower limb exercise of the triceps surae. One leg performed sustained static contractions at a constant long muscle length (ISO), whereas the contralateral leg performed a bout of eccentric heel drop exercise (ECC). Time under tension was matched between the ECC and ISO conditions. Seven days later, both legs performed ECC. Plantar flexor twitch torque, medial gastrocnemius (MG) fascicle length and muscle soreness were assessed before, 2 h and 2 days after each exercise bout. MG fascicle length and triceps surae surface electromyography were examined across the bouts of exercise.

RESULTS

We found that both ECC and ISO conditions elicited EIMD and a RBE. ISO caused less damage 2 h after the initial bout (14% less drop in twitch torque, P = 0.03) and less protection from soreness 2 days after the repeated bout (56% higher soreness, P = 0.01). No differences were found when comparing neuromechanical properties across exercise bouts.

CONCLUSION

For MG, the action of stretching an active muscle seems to be more important for causing damage than a sustained contraction at a long length.

The torque-frequency relationship is impaired similarly following two bouts of eccentric exercise: No evidence of a protective repeated bout effect

High-intensity eccentric exercise can lead to muscle damage and weakness. The 'repeated bout effect' (RBE) can attenuate these impairments when performing a subsequent bout. The influence of eccentric exercise-induced muscle damage on low-frequency force production is well-characterized; however, it is unclear how eccentric exercise and the RBE affect torque production across a range of stimulation frequencies (i.e., the torque-frequency relationship). We investigated the influence of an initial (Bout 1) and repeated bout (Bout 2) of eccentric exercise on the elbow flexor torque-frequency relationship. Eleven males completed two bouts of high-intensity eccentric elbow flexions, 4 weeks apart. Torque-frequency relationships were constructed at baseline and 0.5, 24, 48, 72, 96, and 168 h following both bouts via percutaneous stimulation at 1, 6, 10, 20, 30, 40, 50, and 100 Hz. Serum creatine kinase activity, self-reported muscle soreness, and isometric maximum voluntary contraction torque indirectly inferred the presence of muscle damage following Bout 1, and attenuation of muscle damage following Bout 2. Torque amplitude at all stimulation frequencies was impaired 30 min following eccentric exercise, however, torque at lower (1-10 Hz) and higher frequencies (40-100 Hz) recovered within 24 h while torque across the middle frequency range (20-30 Hz) recovered by 48 h. No between-bout differences were detected in absolute or normalized torque at any stimulation frequency, indicating no protective RBE on the elbow flexor torque-frequency relationship.

Large increases in plasma fast skeletal muscle troponin I after whole-body eccentric exercises

OBJECTIVES

It has been reported that plasma fast skeletal muscle troponin I (fsTnI) but not slow skeletal muscle troponin I (ssTnI) increases after a bout of eccentric exercise of the elbow flexors. The present study compared the first and second bouts of whole-body eccentric exercises for changes in plasma fsTnI and ssTnI concentrations.

DESIGN

Observational study in an experimental group.

METHODS

Fifteen sedentary men (20-25 y) performed nine eccentric exercises targeting arm, leg and trunk muscles, and repeated them two weeks later. Blood samples were taken before and for five days following each bout, and plasma ssTnI and fsTnl concentrations were measured by enzyme-linked immunosorbent assays. Their changes were compared between bouts and their relationships to plasma CK activity and myoglobin concentrations were analysed.

RESULTS

Plasma fsTnI concentration increased after the first bout and peaked at 4 days post-exercise (2152-40,295 ng/mL), but no significant increases were evident after the second bout. Plasma ssTnI concentration did not change significantly from the baseline (<0.08 ng/mL) after either bout. Peak plasma fsTnI concentration was significantly (p < 0.005) correlated with peak plasma CK activity (peak: 23,238-207,304 IU/L, r = 0.727) and myoglobin concentration (1047-3936 μg/L, r = 0.625) after the first bout.

CONCLUSIONS

These results suggest that plasma TnI concentrations are more specific biomarker of muscle damage than plasma CK activity and myoglobin concentration. It seems that the whole-body eccentric exercises induced damage preferentially to fast-twitch muscle fibres, and increases in plasma CK activity and myoglobin concentration after eccentric exercise may reflect fast-twitch muscle fibre damage.

Changes in central and peripheral neuromuscular fatigue indices after concentric versus eccentric contractions of the knee extensors

PURPOSE

To better understand neuromuscular characteristics of eccentric exercise-induced muscle damage, this study compared between concentric (CONC) and eccentric (ECC) exercises of knee extensor muscles, and the first (ECC1) and second bouts of the eccentric exercise (ECC2) for central and peripheral parameters associated with neuromuscular fatigue.

METHODS

Twelve young men performed three exercise bouts separated by at least 1 week between CONC and ECC1, and 2 weeks between ECC1 and ECC2. In each exercise, maximal voluntary concentric or eccentric contractions of the knee extensors were performed until a reduction in maximal voluntary isometric contraction (MVC) torque of at least 40% MVC was achieved immediately post-exercise. MVC torque, central (voluntary activation and normalised electromyographic activity), and peripheral neuromuscular indices (evoked torque and M-wave amplitude), and muscle soreness were assessed before (PRE), immediately after (POST), 1 h (1H), and 1-4 days after exercise (D1, D2, D3, and D4).

RESULTS

MVC torque decreased at only POST for CONC (- 52.8%), but remained below the baseline at POST (- 48.6%), 1H (- 34.1%), and D1-D4 (- 34.1 to - 18.2%) after ECC1, and at POST (- 45.2%), 1H (- 24.4%) and D1 (- 13.4%) after ECC2 (p < 0.05). Voluntary activation decreased immediately after ECC1 (- 21.6%) and ECC2 (- 21.1%), but not after CONC. Electrically evoked torques decreased similarly at POST and 1H for the three conditions, but remained below the baseline at D1 only post-ECC1.

CONCLUSION

These results showed that both central and peripheral factors contributed to the MVC decrease after ECC1 and ECC2, but the decrease was mainly due to peripheral factors after CONC.

The effect of slope on repeated sprint ability in young soccer players

This study aimed to describe a gradient repeated sprint ability (RSA) test in comparison with a standard level one by investigating performance, metabolic demand and muscular jumping performance as a proxy for running mechanics. Eighteen athletes performed two level RSA tests (40 m × 6) - for reliability evaluation - and one ±5% gradient RSA test, second leg downhill (RSAgrad). Rating of perceived exertion (RPE), blood lactate concentration (BLa) concentration, vertical jump heights were assessed as well. Level test measures resulted highly reliable (Intra-class correlation coefficient (ICC) ≥0.96). RSAgrad worsened only first sprints' performance (-2%) but not overall test performance (~45 s). RSAgrad resulted to be less deteriorating in terms of fatigue index (FI) (-36%), BLa (-23%), RPE (-11%), jumping performance (RSAgrad post-/pre-squat jump, countermovement jump heights (CMJh): -3%, -6%, respectively). RSAgrad could be used to diversify common training protocol without stressing excessively athletes' current metabolic-anaerobic capacity. Such physical conditioning procedures could improve acceleration/braking capability.

Influence of repeated bouts of eccentric exercise on high-intensity aerobic performance

[Purpose] It is believed that eccentric high-intensity exercise can decrease performance in subsequent exercise. However, with repetition, the deleterious effects can be minimized. Thus, this study evaluated the influence of repeated bouts of eccentric exercise on subsequent high-intensity aerobic performance. [Subjects and Methods] Seven healthy and sedentary male volunteers were recruited. a) Visit 1: determination of maximum oxygen uptake (VO2max) and speed associated with maximum oxygen uptake (vVO2max) in incremental treadmill testing; b) Visit 2: run to exhaustion at vVO2max (Tlim control); c) Visit 3: 10 sets of 10 depth jumps, followed by a run to exhaustion at vVO2max (Tlim 1); d) Visit 4: after 6 weeks without any physical training, the volunteers carried out the same procedures as on the third visit (Tlim 2). Data were analyzed using one-way analysis of variance (ANOVA) with the post-hoc Tukey test. [Results] Significant differences were found between Tlim control and Tlim 1 (283.4 ± 47.7 s vs. 125.2 ± 64.1 s, respectively), these were not different from Tlim 2. [Conclusion] Eccentric exercise showed deleterious effects on subsequent high-intensity aerobic performance. These effects were minimized after the exercise protocol was repeated 6 weeks after the first event.

Muscle damage and repeated bout effect following blood flow restricted exercise

PURPOSE

Blood-flow restricted resistance exercise training (BFRE) is suggested to be effective in rehabilitation training, but more knowledge is required about its potential muscle damaging effects. Therefore, we investigated muscle-damaging effects of BFRE performed to failure and possible protective effects of previous bouts of BFRE or maximal eccentric exercise (ECC).

METHODS

Seventeen healthy young men were allocated into two groups completing two exercise bouts separated by 14 days. One group performed BFRE in both exercise bouts (BB). The other group performed ECC in the first and BFRE in the second bout. BFRE was performed to failure. Indicators of muscle damage were evaluated before and after exercise.

RESULTS

The first bout in the BB group led to decrements in maximum isometric torque, and increases in muscle soreness, muscle water retention, and serum muscle protein concentrations after exercise. These changes were comparable in magnitude and time course to what was observed after first bout ECC. An attenuated response was observed in the repeated exercise bout in both groups.

CONCLUSION

We conclude that unaccustomed single-bout BFRE performed to failure induces significant muscle damage. Additionally, both ECC and BFRE can precondition against muscle damage induced by a subsequent bout of BFRE.