The repeated bout effect can occur without mechanical and neuromuscular changes after a bout of eccentric exercise

Abstract

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.

Low frequency fatigue and changes in muscle fascicle length following eccentric exercise of the knee extensors

“…Nevertheless, we saw no evidence of a change in the force–length relationship based on knee angle (Figure 5a). The reason for the difference between the present and previous reports is not obvious but there are other reports of no change in optimal angle following eccentric exercise in man (Hoffman et al., ; Pincheira et al., ) and rat (Rijkelijkhuizen et al., ). It may also be related to the fact that there is considerable muscle shortening during isometric contractions, the extent of which may differ between conditions, so that knee angle may not be a reliable measure of muscle length.…”

“…The difficulty with this line of argument, however, is that the 20/100 ratio can be influenced by a number of factors, one being the length of the muscle, which has been reported to change, as indicated by an increase in the optimum length for force production, following eccentric exercise (Philippou, Bogdanis, Nevill, & Maridaki, 2004;Prasartwuth, Allen, Butler, Gandevia, & Taylor, 2006;Proske & Morgan, 2001;. There are, however, other reports finding no change in optimal angle following eccentric exercise in man (Hoffman, Cresswell, Carroll, & Lichtwark, 2016;Pincheira et al, 2018) and rat (Rijkelijkhuizen, de Ruiter, Huijing, & de Haan, 2005).…”

Regional changes in muscle activity do not underlie the repeated bout effect in the human gastrocnemius muscle

“…Compared to upper limb muscles, lower limb muscles are inherently more resistant to muscle damage, 5 despite significant pain occurring in response to naïve eccentric exercise 6‐8 . In the triceps surae, this may be due to its muscle architectural features (eg, pennate muscle fibers, muscle,‐tendon interaction) or the relatively high exposure to prior activities involving lengthening contractions (such as locomotion) 9 .…”

“…In the triceps surae, this may be due to its muscle architectural features (eg, pennate muscle fibers, muscle,‐tendon interaction) or the relatively high exposure to prior activities involving lengthening contractions (such as locomotion) 9 . Interestingly however, the RBE is still present in this muscle group, even after arguably lower levels of exercise‐induced muscle damage 6,7 . Thus, the triceps surae might adapt in a way different to other models of muscle damage where the muscle is more prone to damage (eg, upper limb muscles and animal models where the distal tendon is detached and stretched to excessive lengths).…”

Eccentric Resistance Training in Youth: Perspectives for Long-Term Athletic Development

“…Mechanisms explaining this improved response may include neural, muscle-tendon complex behaviours, extracellular matrix structural remodelling and a modified inflammatory response [150]. Although the specific mechanisms that are responsible for the RBE are unclear, it would appear that the RBE is multifactorial which is likely to be highly muscle and exercise specific [154]. The beneficial effects conveyed by the RBE is characterized by factors such as faster recovery of muscle strength and ROM, reduced increases in muscle proteins in the blood, and less significant development of swelling and muscle soreness [152,155].…”