Recent advances in the understanding of the repeated bout effect: the protective effect against muscle damage from a single bout of eccentric exercise

Abstract

The repeated bout effect refers to the adaptation whereby a single bout of eccentric exercise protects against muscle damage from subsequent eccentric bouts. While the mechanism for this adaptation is poorly understood there have been significant recent advances in the understanding of this phenomenon. The purpose of this review is to provide an update on previously proposed theories and address new theories that have been advanced. The potential adaptations have been categorized as neural, mechanical and cellular. There is some evidence to suggest that the repeated bout effect is associated with a shift toward greater recruitment of slow twitch motor units. However, the repeated bout effect has been demonstrated with electrically stimulated contractions, indicating that a peripheral, non-neural adaptation predominates. With respect to mechanical adaptations there is evidence that both dynamic and passive muscle stiffness increase with eccentric training but there are no studies on passive or dynamic stiffness adaptations to a single eccentric bout. The role of the cytoskeleton in regulating dynamic stiffness is a possible area for future research. With respect to cellular adaptations there is evidence of longitudinal addition of sarcomeres and adaptations in the inflammatory response following an initial bout of eccentric exercise. Addition of sarcomeres is thought to reduce sarcomere strain during eccentric contractions thereby avoiding sarcomere disruption. Inflammatory adaptations are thought to limit the proliferation of damage that typically occurs in the days following eccentric exercise. In conclusion, there have been significant advances in the understanding of the repeated bout effect, however, a unified theory explaining the mechanism or mechanisms for this protective adaptation remains elusive.

A light load eccentric exercise confers protection against a subsequent bout of more demanding eccentric exercise

“…1,3 When eccentric exercise is repeated, the magnitude of changes in the markers is smaller and recovery of muscle function is faster compared to the initial bout. 1,4 This protective effect is often referred to as the repeated bout effect, 1,4 and is known to last for several months for the case of maximal eccentric exercise of the elbow flexors. 5 It has been reported that a reduced number of maximal eccentric contractions can provide a protective effect against a larger number of maximal contractions.…”

Individual analysis of creatine kinase concentration in Brazilian elite soccer players

“…The reduction of CK concentration observed over time in this study may be ascribed to muscle adaptation 26 , which has been observed in protocols of eccentric exercise 27 and in soccer players during a Brazilian first-division championship 10 . One of the mechanisms responsible for muscle adaptation can be derived from the activation of myogenic satellite cells that act in the repair of damaged muscle fibers 28 .…”

Lower-volume muscle-damaging exercise protects against high-volume muscle-damaging exercise and the detrimental effects on endurance performance

“…CK activity after the second bout of high volume squatting was reduced by the initial lower volume bout, meaning it is unlikely that the RBE was exclusively due to the removal and replacement of weak sarcomeres as proposed by some studies (e.g. Armstrong et al 1983;Byrnes et al 1985;McHugh et al 2003;McHugh et al 1999). Indeed, if weak sarcomeres were still intact after the lower volume bout of squatting then they would have been damaged during the more strenuous high volume bout (Nosaka et al 2001).…”

“…Therefore, the lower CK in Bout 2 suggests that the initial stress in Bout 1, albeit of a lower intensity, provided a stimulus to strengthen the muscle cell membrane against further damage (Clarkson and Tremblay 1988;Howatson et al 2007). The protective effect of lower volume muscle-damaging exercise against subsequent high volume exercise could also be due to changes in motor unit recruitment during squatting Bout 2 (Chen 2003;Howatson et al 2007;McHugh 2003;McHugh et al 1999). Unfortunately EMG activity was measured during running and not the damaging exercise, which means that we are unable to confirm if alterations in motor unit activity occurred.…”

“…It is well established that the signs and symptoms of exercise-induced muscle damage (EIMD) are attenuated after a repeated bout of muscle-damaging exercise (McHugh 2003;McHugh et al 1999). These adaptations are now known to be extended to the observed effects of EIMD on running performance, whereby the negative alterations in the physiological, metabolic, perceptual and kinematic responses during fixed-intensity running are reduced after a repeated bout of EIMD performed two weeks later (Burt et al 2013).…”