Rate of Force Development as an Indicator of Neuromuscular Fatigue: A Scoping Review

Abstract

Because rate of force development (RFD) is an emerging outcome measure for the assessment of neuromuscular function in unfatigued conditions, and it represents a valid alternative/complement to the classical evaluation of pure maximal strength, this scoping review aimed to map the available evidence regarding RFD as an indicator of neuromuscular fatigue. Thus, following a general overview of the main studies published on this topic, we arbitrarily compared the amount of neuromuscular fatigue between the “gold standard” measure (maximal voluntary force, MVF) and peak, early (≤100 ms) and late (>100 ms) RFD. Seventy full-text articles were included in the review. The most-common fatiguing exercises were resistance exercises (37% of the studies), endurance exercises/locomotor activities (23%), isokinetic contractions (17%), and simulated/real sport situations (13%). The most widely tested tasks were knee extension (60%) and plantar flexion (10%). The reason (i.e., rationale) for evaluating RFD was lacking in 36% of the studies. On average, the amount of fatigue for MVF (−19%) was comparable to late RFD (−19%) but lower compared to both peak RFD (−25%) and early RFD (−23%). Even if the rationale for evaluating RFD in the fatigued state was often lacking and the specificity between test task and fatiguing exercise characteristics was not always respected in the included studies, RFD seems to be a valid indicator of neuromuscular fatigue. Based on our arbitrary analyses, peak RFD and early phase RFD appear even to be more sensitive to quantify neuromuscular fatigue than MVF and late phase RFD.

The role of age on neuromuscular performance decay induced by a maximal intensity sprint session in a group of competitive endurance athletes

“…13 Additionally, early RTD (≤100 ms from the onset of contraction), largely dependent on motor unit recruitment speed and maximal discharge rate, showed a greater sensibility to exercise-induced fatiguability compared to late RTD (>100 ms from the onset of contraction), more dependent on muscle-tendon units structural variables. 12 Significant decreases in RTD have been observed after endurance exercise (e.g., running), [14][15][16] and after high-intensity intermittent exercise. [17][18][19][20] In both cases, the drop in RTD, particularly early RTD, exceeded that of MVF.…”

“…9 Such changes may consequently lead to alterations and, in particular, reductions in motor performances and abilities (e.g., drop-in strength and power, increased fatiguability). 9,10 Neuromuscular fatigue, or fatiguability, 11 has been defined as the exercise-induced decline in the maximal isometric contraction (MVC) force or torque (MVT) of a muscle or muscle group, 12 and both, drops in peak torque during MVCs, and drops in the rate of torque development (RTD) after exercise have been associated with fatiguability. 12 In this regard, age-related changes in neural activation, maximal and explosive strength, as well as a reduction in force or power of a muscle or muscle group in response to exercise (i.e., fatiguability) have been described.…”

“…9,10 Neuromuscular fatigue, or fatiguability, 11 has been defined as the exercise-induced decline in the maximal isometric contraction (MVC) force or torque (MVT) of a muscle or muscle group, 12 and both, drops in peak torque during MVCs, and drops in the rate of torque development (RTD) after exercise have been associated with fatiguability. 12 In this regard, age-related changes in neural activation, maximal and explosive strength, as well as a reduction in force or power of a muscle or muscle group in response to exercise (i.e., fatiguability) have been described. 9 In particular, the RTD seems to be more susceptible to exercise-induced neuromuscular fatigue than maximal voluntary torque (MVT), 12 and more sensitive to detect fatigue response changes induced by age.…”

“…12 In this regard, age-related changes in neural activation, maximal and explosive strength, as well as a reduction in force or power of a muscle or muscle group in response to exercise (i.e., fatiguability) have been described. 9 In particular, the RTD seems to be more susceptible to exercise-induced neuromuscular fatigue than maximal voluntary torque (MVT), 12 and more sensitive to detect fatigue response changes induced by age. 13 Additionally, early RTD (≤100 ms from the onset of contraction), largely dependent on motor unit recruitment speed and maximal discharge rate, showed a greater sensibility to exercise-induced fatiguability compared to late RTD (>100 ms from the onset of contraction), more dependent on muscle-tendon units structural variables.…”

“…[17][18][19][20] In both cases, the drop in RTD, particularly early RTD, exceeded that of MVF. 12 Thus, from one side, drop-in neuromuscular function markers (i.e., MVF and RTD) are reliable indicators of exercise-induced fatiguability, and on the other, to be a valid tool to evaluate the impact of age on the neuromuscular system functions in response to exercise-induced fatigue. 9,12 Traditionally, coupled to maximal and explosive strength assessment, electromyographic signals are acquired and analysed to evaluate exercise-induced fatiguability.…”