Neuromechanics of The Rate of Force Development

Abstract

The rate of force development varies greatly across individuals. In the present review, we discuss the neuromechanical factors that explain this variability.

Decreased neural drive affects the early rate of force development after repeated burst‐like isometric contractions

“…The nervous system can produce rapid muscle contraction by compressing the motor unit recruitment and abruptly increasing the discharge rate 21 . These mechanisms are associated with the neural drive to the muscle, which is the primary determinant of early RFD 22 .…”

“…In turn, spinal and supraspinal mechanisms have likely lowered the motor unit recruitment and discharge rate in the first phase of voluntary contractions. It is unsurprising that repetitive explosive contractions impair the neural drive as neural drive is the main determinant of rapid contractions 20,21,44 . Indirect evidence of decreased muscle excitation and motor unit recruitment occurrence could also be found in the significant drop of normalized RMS ( d ~ 1.0) and normalized MFCV ( d ~ 0.6) over the first 50–100 ms of contractions.…”

“…27,30 Lastly, to test any reduction in neural drive to the muscle during the rapid force production, we calculated the so-called neural efficacy, which consists of the ratio between voluntary and octets-evoked RFD in the first 50 ms of contractions. 31,32 As the force production in the first 50 ms of contraction primarily depends on the neural drive to the muscles, 21,22 we hypothesized that repeated rapid contractions mostly induced a decrement in the net neural drive with the consequence of lowering the early phase RFD (i.e., the first 50 ms of force production).…”

“…Rapid muscle contractions are characterized by specific rapid motor unit recruitment and discharge rate 21,22 . When the motor unit firing frequency is high, i.e., in the first 50 ms from contraction onset, 21,22 the absolute force production is still relatively low. Therefore, reaching maximal forces is unnecessary to stress the mechanisms of contraction rapidity if at least 70%–80% of MVF is targeted 19 .…”

Plyometric Exercises: Optimizing the Transfer of Training Gains to Sport Performance

“…The RFD often is used as an index of "explosive" force for such actions (11)(12)(13). The RFD is influenced by several factors, such as the intensity of voluntary activation (12,14,15), the speed-related properties of the muscle (11,16,17), and the characteristics of the series elastic component of the muscle-tendon unit (18,19). The relative contribution of these variables to the instantaneous force produced varies during the time course of the contraction (11,17).…”