Does muscle growth mediate changes in a nonspecific strength task?

Abstract

AbstractThe purpose of this study was to determine if muscle growth mediates increases in a strength task which was not directly trained. One hundred fifty‐one participants were randomized into control, one‐repetition maximum training (1RM‐TRAIN), or traditional training (TRAD‐TRAIN). Training groups performed isotonic elbow flexion 3x/week for 6 weeks. Anterior muscle thickness at 50%, 60% and 70% upper arm length, and maximal isokinetic torque at 60°/sec were assessed pre‐ and post‐training. Change‐score mediation models (adjusted for sex, pre‐muscle thickness, and pre‐strength) were constructed for each muscle thickness site. The effects of each training group were evaluated relative to the control. Data is presented as coefficient (95% CI). There were no significant relative direct effects on nonspecific strength for either training group outside of the 60% model (1.7 [0.13, 3.27] Nm). The relative effect of 1RM‐TRAIN on muscle thickness was greater in 60% (0.09 [0.01, 0.17] cm) and 70% (0.09 [0.00, 0.17] cm) models; while TRAD‐TRAIN was greater in all three: (50% = 0.24 [0.15, 0.32]; 60% = 0.24 [0.16, 0.33]; 70% = 0.22 [0.14, 0.31] cm). The effect of muscle thickness on nonspecific strength was only significant for the 60% (−3.06 [−5.7, −0.35] Nm) model. The relative indirect effect on nonspecific strength was not significant for the 1RM‐TRAIN or TRAD‐TRAIN. Similar to previous findings on specific strength, we did not find evidence for a mediating effect of muscle growth on training induced increases in nonspecific strength. The importance of muscle growth for changes in nonspecifically trained strength may need to be reconsidered.