Evaluation of novel tests of neuromuscular function based on brief muscle actions

Abstract

Although widely used, the standard strength test (SST) is known to provide moderate correlations with functional measures, while being based on sustained maximum forces and a relatively large number of trials. The aim of this study was to compare the concurrent (with respect to SST) and external validity (with respect to the standard balance and maximum power output tests) of 2 alternate tests of neuromuscular function based on brief isometric actions. The first test provides a slope between the rates of torque development (RTD) and peak torques (T) measured from a number of consecutive rapid actions performed across a wide range of T levels (brief force pulses, BFP). The second test (alternating consecutive maximum contractions, ACMC) provides T and RTD from multiple cycles of rapid alternating maximum actions of 2 antagonistic muscle groups. The results obtained from 29 young and healthy subjects revealed moderate-to-high concurrent validity of ACMC (median r = 0.56, p < 0.05) and its similar, if not higher external validity than SST. Conversely, both the concurrent and external validity of BFP seemed to be relatively low (r = 0.23, p > 0.05). Because ACMC could also have advantage over SST by being based on somewhat lower and transitional muscle forces exerted and fewer trials are needed for testing 2 antagonistic muscles, the authors conclude that ACMC could be considered as either an alternative or complementary test to SST for testing the ability for rapid exertion of maximum forces. Conversely, BFP may offer a measure of the neuromuscular system "as a whole" that is complementary to SST by providing outcomes that are relatively independent of muscle size and function.

Figure 1

Force-time curves (thick line, left hand axis) and their derivatives (thin line, right hand axis) observed from a representative subject when performing (A) the standard strength test (SST), (B) the brief force pulses in the direction of extension (BFP), (C) the alternating consecutive maximum contractions test (ACMC). The data depicting the direction of flexion are shown as negative. Panel (D) shows the slopes and intercepts of a regression line calculated from the peaks of each force pulse and corresponding rate of force development.