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

Abstract

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 joint's 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.

Keywords: Cross-bridge theory; Eccentric contraction; Force-length relationship; Isometric force; Muscle properties.

Graphical abstract

Fig. 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram of studies search and selection.

Fig. 2

Estimates of differences in torque capacity between purely isometric contractions and isometric contractions preceded by stretching. All comparisons included were for voluntary contractions. Positive values indicate the magnitude of residual torque enhancement (torque is greater in isometric contractions preceded by an active stretch when compared to purely isometric contractions). ^a indicates the use of multi-joint contractions. 95%CI = 95% confidence interval; RTE = residual torque enhancement; SMD = standardized mean difference.

Fig. 3

A significant publication bias was verified for the voluntary contractions (Egger's test of the intercept with p = 0.019). Funnel plots show gray scatter dots, which are studies included in the meta-analysis, and white scatter dots, which are imputed studies mirrored for each trimmed study in order to reach funnel plot symmetry.

Fig. 4

Estimates of differences in torque produced between purely isometric contractions and isometric contractions preceded by stretching. All comparisons included were for electrically evoked contractions. Positive values indicate the magnitude of residual torque enhancement (torque is greater in isometric contractions preceded by an active stretch when compared to purely isometric contractions). 95%CI = 95% confidence interval; RTE = residual torque enhancement; SMD = standardized mean difference.

Fig. 5

Bubble plots with fitted meta-regression line indicating the effect of stretching amplitude on the standardized mean difference in torque produced between purely isometric contractions and contractions preceded by stretching, (A) voluntary contractions and (B) electrically evoked contractions. The size of each point is inversely proportional to the variance of the estimated difference.