A comparison of maximal rate of force development between burst and maximum voluntary contractions: reliability and...

Explosive strength, measured as the maximal rate of torque development (RTD_max), can be assessed during rapid isometric contractions (bursts) or high-force maximum voluntary isometric contractions (MVIC). However, the ideal approach for assessing knee extensor RTD_max in trained individuals with respect to the reliability, RTD_max output, and neuromuscular activation is unclear. Thus, the purpose of this study was to compare inter-session test-retest reliability, RTD_max output, and neuromuscular activation between burst and MVIC methods.

Trained (n = 30; females: n = 13) participants completed knee extension MVIC and burst contractions. Neuromuscular activation was assessed by the rate of rise of the electromyography (EMG) root mean square (RMS) signal normalized to the intra-repetition peak EMG rms amplitude (RER_max) for the vastus lateralis (VL) and vastus medialis (VM). RTD_max was computed from the derivative of the torque-time curve as the average RTD around the instant of the peak RTD using a ± 25 ms window.

RTD_max demonstrated excellent test-retest reliability for MVIC (right limb: ICC = 0.87; left limb: ICC = 0.93) and burst (right limb: ICC = 0.86; left limb: ICC = 0.88) contractions. Across limbs and sessions, RTD_max and RER_max were significantly greater (p < 0.01) with the burst method (RTD_max = 1751 Nm·s^- 1; VL RER_max = 382%RMS_max·s^- 1; VM RER_max = 403%RMS_max·s^- 1) compared to the MVIC method (RTD_max = 1493 Nm·s^- 1; VL RER_max = 309%RMS_max·s^- 1; VM RER_max = 343%RMS_max·s^- 1).

Burst contractions provide an advantage over traditional MVICs for assessing the true knee extensor explosive strength.