The effects of varying time under tension and volume load on acute neuromuscular responses

The purpose of this study was to examine the effects of different methods of measuring training volume, controlled in different ways, on selected variables that reflect acute neuromuscular responses. Eighteen resistance-trained males performed three fatiguing protocols of dynamic constant external resistance exercise, involving elbow flexors, that manipulated either time-under-tension (TUT) or volume load (VL), defined as the product of training load and repetitions. Protocol A provided a standard for TUT and VL. Protocol B involved the same VL as Protocol A but only 40% concentric TUT; Protocol C was equated to Protocol A for TUT but only involved 50% VL. Fatigue was assessed by changes in maximum voluntary isometric contraction (MVIC), interpolated doublet (ID), muscle twitch characteristics (peak twitch, time to peak twitch, 0.5 relaxation time, and mean rates of force development and twitch relaxation). All protocols produced significant changes (P ≤ 0.05) in the measures considered to reflect neuromuscular fatigue, with the exception of ID. Fatigue was related to an increase in either TUT or VL with greater fatigue, as reflected by MVIC and peripheral measures, being associated with differences in TUT. The lack of change in ID suggests that fatigue was more related to peripheral than central mechanisms. It was concluded that the load and contraction velocities of the repetitions have different effects on acute neuromuscular responses and should, therefore, be clearly calculated when describing training volume for dynamic constant external resistance exercise training.