Myofiber Permeability and Force Production of Rat Muscles Following Eccentric Contractions: The Repeated Bout Effect Depends on the Interval

Past eccentric contraction (ECC)-induced muscle injury reduces the severity of symptoms of subsequent muscle injury;this phenomenon is known as a repeated bout effect (RBE). It has been reported that increases in the duration of the interval between the first and second bouts are linked to weakening of the RBE. However, the histology following the attenuation of the RBE remains unclear. We examined the sustained effects of the second bout with regard to myofiber permeability and muscle force. Sixty-four male rats were randomly assigned to eight groups that varied in the number of exercise sessions and the duration of the interval between the first and second bouts: the non-ECC (Control);the single-injury (Post 1st bout);groups that were allowed to recover for 1, 2, and 4 weeks after a single injury (Pre 2nd bout_1w, Pre 2nd bout_2w, and Pre 2nd bout_4w);and groups that were subjected to second injuries 1, 2, and 4 weeks after the first (Post 2nd bout_1w, Post 2nd bout_2w, and Post 2nd bout_4w). The tibialis anterior was electrically stimulated in each ECC group. Twenty-four hours before muscle sampling, Evans blue dye (EBD) (a marker of myofiber damage) was administered. The maximal isometric contraction tension was measured immediately before sampling. The number of EBD-positive (+) fibers was determined via histological analysis. An RBE was revealed by functional examination at the 1- and 2-week and histological examination at the 1-, 2-, and 4-week time points (P < 0.05). In terms of myofiber permeability, prolongation of the interval before the second bout weakened this effect (P < 0.05). Experiments with 1-, 2-, and 4-week intervals indicated that prolongation of the interval before the second bout weakened the RBE with regard to myofiber permeability.

Residual force enhancement in human skeletal muscles:A systematic review and meta-analysis

Objective:We reviewed and appraised the existing evidence of in vivo manifestations of residual force enhancement in human skeletal muscles and assessed,through a meta-analysis,the effect of an immediate history of eccentric contraction on the subsequent torque capacity of voluntary and electrically evoked muscle contractions.Methods:Our search was conducted from database inception to May 2020.Descriptive information was extracted from,and quality was assessed for,45 studies.Meta-analyses and metaregressions were used to analyze residual torque enhancement and its dependence on the angular amplitude of the preceding eccentric contraction.Results:Procedures varied across studies with regards to muscle group tested,angular stretch amplitude,randomization of contractions,time window analyzed,and verbal command.Torque capacity in isometric(constant muscle tendon unit length and joint angle)contractions preceded by an eccentric contraction was typically greater compared to purely isometric contractions,and this effect was greater for electrically evoked muscle contractions than voluntary contractions.Residual torque enhancement differed across muscle groups for the voluntary contractions,with a significant enhancement in torque observed for the adductor pollicis,ankle dorsiflexors,ankle plantar flexors,and knee extensors,but not for the elbow and knee flexors.Meta-regressions revealed that the angular amplitude of the eccentric contraction(normalized to the respective joints full range of motion)was not associated with the residual torque enhancement observed.Conclusion:There is evidence of residual torque enhancement for most,but not all,muscle groups,and residual torque enhancement is greater for electrically evoked than for voluntary contractions.Contrary to our hypothesis,and contrary to generally accepted findings on isolated muscle preparations,residual torque enhancement in voluntary and electrically evoked contractions does not seem to depend on the angular amplitude of the preceding eccentric contraction.

Eccentric training with a powered rowing machine

The aim of this study was to investigate the effects of eccentric workloads generated by a powered rowing machine on the cardiorespiratory,cardiovascular and musculoskeletal systems.It was hypothesized that beneficial physiological effects would result by training with high eccentric workloads.Conventional rowing machines are utilized for performance improvements through concentric workloads alone;however for this research,a conventional machine was modified with an electric motor and an advanced control system to allow the machine to also include eccentric capabilities.The ability to combine concentric and eccentric actions in any exercise has the potential to improve training effectiveness.The study followed an experimental design,exposing ten subjects(5 male,5 female)to multiple eccentric workloads generated by the powered rowing machine.Each subject participated in two 12-min exercise trials corresponding to full body row(FBR)and low body row(LBR).Each of these trials included four 3-min stages that gradually increased the eccentric workload.Increased eccentric muscle contractions and metabolic cost were confirmed in the experiments.The results on oxygen consumption reveal a significant increase between stages 1 and 2 for both exercises(FBR p=0.0001 and LBR p=0.004)with no significant increases between the remaining stages.Results on heart rate reveal a significantly increase with each stage for both exercises(p=<0.05).Results on muscle activation also reveal an overall increase for all muscle groups as eccentric workload is increased.