The rate of force development scaling factor: a review of underlying factors, assessment methods and potential for practical applications

Abstract

When humans perform isometric ballistic contractions of different intensities, a strong linear relationship is observed between peak force and peak rate of force development. The slope of this relationship, termed the rate of force development scaling factor (RFD-SF), has been proposed as a measure of neuromuscular quickness of submaximal contractions. The RFD-SF is largely dependent on motor unit firing rate and its modulation with contraction intensity, and possibly by agonist-antagonist coordination. The purpose of this review was to critically evaluate the available literature on RFD-SF, including the underlying physiological mechanisms, assessment protocols and methodological considerations, practical application to clinical and sports practice and additional factors such as sex, muscle group, task and fatigue. The main findings of the review are: (a) RFD-SF is very sensitive to impairments associated with aging and neurological diseases, (b) the literature lacks studies on the importance of RFD-SF for athletes, with some evidence that RFD-SF may affect the accuracy of submaximal movements, (c) RFD-SF is not largely influenced by fatigue and sex, (d) the RFD-SF values have been very consistent across muscle groups, with an exception of ankle muscles, (e) the methodology for RFD-SF assessment appears to be well established and standardized. Future research is needed to determine if RFD-SF provides any independent information that cannot be captured with peak force/torque and RFD.

Deficits in rate of force production during multifinger tasks are associated with cognitive status

“…19 The rate at which force can be generated therefore provides a more sensitive measure of age-related changes in neural sufficiency than force magnitude. 20 Consistent with this supposition, age-dependent (60-81 vs. 21-37 years) differences in the maximum rate of force development (η 2 = 0.51) recorded in a grip task (engaging digits II to IV together) are markedly larger than differences in maximum level of force (η 2 = 0.09). 21 It is therefore hypothesised that a measure of the MFFD that is derived from the maximum rate at which force is generated will be more sensitive to individual differences in cognitive function, than a MFFD calculated from the maximum level of force.…”

“…Although attributable in part to a disproportionate atrophy of fast‐twitch muscle fibres and reductions in the contractile velocity of single muscle fibres, deficiencies in central drive also play a determining role 19 . The rate at which force can be generated therefore provides a more sensitive measure of age‐related changes in neural sufficiency than force magnitude 20 . Consistent with this supposition, age‐dependent (60–81 vs. 21–37 years) differences in the maximum rate of force development (η 2 = 0.51) recorded in a grip task (engaging digits II to IV together) are markedly larger than differences in maximum level of force (η 2 = 0.09) 21 .…”

Reliability of ankle dorsiflexor muscle strength, rate of force development, and tibialis anterior electromyography after stroke

“…24 Data processing methods also differed between the studies. Mentiplay and colleagues HHD method sampled force data at only 40 Hz, 20,21 much lower than recommended, 24,30 and then interpolated this to equate 1000 Hz, which may have increased reliability. Our study analysed RFD in the first 200ms, whereas Mentiplay et al 20 scanned successive 200ms windows to find the peak RFD, a method that excludes movement onset and any associated artefacts or issues with identifying onset.…”

Effect of mental fatigue on hand force production capacities

“…In this context, protocols using the RFD scaling factor (RFD-SF) provide an appealing approach [ 12 ]. RFD-SF mainly reflects the neural mechanisms of RFD (i.e., motor unit firing rate) and is independent of other RFD determinants, such as maximal strength or muscle fiber type [ 13 ]. Although physical fatigue does not seem to affect the RFD-SF [ 11 ], this latter could be impacted positively by resistance exercise [ 14 ] or negatively by aging [ 15 ].…”