Neuromuscular Fatigue Does Not Impair the Rate of Force Development in Ballistic Contractions of Submaximal Amplitudes

Abstract

The effect of muscle fatigue on rate of force development (RFD) is usually assessed during tasks that require participants to reach as quickly as possible maximal or near-maximal force. However, endurance sports require athletes to quickly produce force of submaximal, rather than maximal, amplitudes. Thus, this study investigated the effect of muscle fatigue induced by long-distance running on the capacity to quickly produce submaximal levels of force. Twenty-one male amateur runners were evaluated before and shortly after a half-marathon race. Knee extensors force was recorded under maximal voluntary and electrically evoked contractions. Moreover, a series of ballistic contractions at different submaximal amplitudes (from 20 to 100% of maximal voluntary force) was obtained, by asking the participants to reach submaximal forces as fast as possible. The RFD was calculated for each contraction. After the race, maximal voluntary activation, resting doublet twitch, maximal force, and RFD during maximal contraction decreased (-12, -12, -21, and -19%, respectively, all P-values < 0.0001). Nevertheless, the RFD values measured during ballistic contractions up to 60% of maximal force were unaffected (all P-values > 0.4). Long-distance running impaired the capacity to quickly produce force in ballistic contractions of maximal, but not of submaximal, amplitudes. Overall, these findings suggest that central and peripheral fatigue do not affect the quickness to which muscle contracts across a wide range of submaximal forces. This is a relevant finding for running and other daily life activities that rely on the production of rapid submaximal contractions rather than maximal force levels.

Interlimb Asymmetries Identified Using the Rate of Torque Development in Ballistic Contraction Targeting Submaximal Torques

“…However, while an imbalance in RTD max might be functionally relevant in many occasions, we argue that it would be important to measure possible interlimb asymmetry in ballistic contractions targeting submaximal, rather than maximal, torque levels. The isometric protocol adopted in this study ( Bellumori et al, 2011 , 2013 ; Casartelli et al, 2014 ; Boccia et al, 2018 ) requested the players to produce a series of ballistic contractions of either submaximal or maximal amplitudes (Figure 2A ). This means that the players performed ballistic contractions targeting, as quickly as possible, from ≈20 to ≈100% of MVC torque.…”

“…Instead, they were asked to produce quick contractions with peak torques reaching approximately a 10% range around the given torque target. As previously reported ( Bellumori et al, 2011 , 2013 ; Casartelli et al, 2014 ; Boccia et al, 2018 ), in the familiarization session, participants practiced until they felt comfortable with the task and could perform discrete ballistic contractions as instructed.…”

“…For the above-mentioned reasons, we suggest that latter ability has higher ecological validity than the RTD max . In this context, the protocol usually adopted to calculate the so-called RTD scaling factor (RTD-SF) provides an appealing approach ( Bellumori et al, 2011 , 2013 ; Casartelli et al, 2014 ; Djordjevic and Uygur, 2017 ; Boccia et al, 2018 ). The protocol consists of a series of ballistic (so called pulses) contractions performed with different submaximal amplitudes (namely from 20 to 100% of maximal isometric torque) ( Freund and Budingen, 1978 ; Wierzbicka et al, 1991 ; Klass et al, 2008 ).…”

“…In each ballistic contraction the individuals are asked to reach a submaximal torque as fast as possible and then to relax their muscles quickly. The RTD produced in each contraction thus provides a measure of the ability to quickly produce torque of submaximal amplitude ( Bellumori et al, 2011 , 2013 ; Casartelli et al, 2014 ; Djordjevic and Uygur, 2017 ; Boccia et al, 2018 ).…”

“…The few intervention studies demonstrated that RTD-SF improved with training on explosiveness and its improvement was related to an increase in motor units discharge rate in the early part of muscle contractions ( Van Cutsem et al, 1998 ; Bellumori et al, 2017 ). Unlike RTD max , RTD-SF is independent of muscle strength ( Bellumori et al, 2011 ; Boccia et al, 2018 ), which facilitates comparisons among different population and muscle groups.…”