Four weeks of high- versus low-load resistance training to failure on the rate of torque development, electromechanical delay, and contractile twitch properties

Abstract

The purpose of this study was to investigate the effects of 4-weeks of high- versus low-load resistance training to failure on rate of torque development (RTD), electromechanical delay (EMD), and contractile twitch characteristics. Fifteen men (mean±SD; age=21.7±2.4 yrs) were randomly assigned to either a high- (80% 1RM; n=7) or low-load (30% 1RM; n=8) training group and completed elbow flexion resistance training to failure 3 times per week for 4 weeks. The participants were tested at baseline, 2-, and 4-weeks of training. Peak RTD (pRTDV) and RTD at 0-30 (RTD30V), 0-50 (RTD50V), 0-100 (RTD100V), and 0-200 (RTD200V) ms, integrated EMG amplitude (iEMG) at 0-30, 0-50, and 0-100 ms, and EMD were quantified during maximal voluntary isometric muscle actions. Peak twitch torque, peak RTD, time to peak twitch, 1/2 relaxation time and the peak relaxation rate were quantified during evoked twitches. Four weeks of high-load, but not low-load resistance training, increased RTD200V. There were also increases in iEMG during the first 30 ms of muscle activation for the high- and low-load groups, which may have indirectly indicated increases in early phase motor unit recruitment and/or firing frequency. There were no significant training-induced adaptations in EMD or contractile twitch properties.

Figure 1

The mean (±standard error) peak rate of torque development (Peak RTD) and RTD calculated in time intervals of 0-30 (RTD30), 0-50 (RTD50), 0-100 (RTD100), and 0-200 (RTD200) ms from the onset of torque production at baseline, 2 weeks, and 4 weeks of training in the [a] 80% 1RM group and [b] the 30% 1RM group. *Indicates a significant increase in RTD200 from baseline to week 4 in the 80% 1RM group. There was also a significant interaction for Peak RTD, although post-hoc analyses on the simple main effects revealed no significant differences.

Figure 2

Mean (±standard error) voluntary electromechanical delay at baseline, 2 weeks, and 4 weeks, in the 80% and 30% 1RM groups.

Figure 3

Mean (±standard error) voluntary electromyographic (EMG) amplitude integrated in time intervals of 0-30 (iEMG30), 0-50 (iEMG50), and 0-100 (iEMG100) ms after the onset of EMG activity collapsed across the 80% and 30% 1RM groups. *Indicates that iEMG30 is significantly greater at weeks 2 and 4 than at baseline.