THE EFFECT OF TEST PROTOCOL INSTRUCTIONS ON THE MEASUREMENT OF MUSCLE FUNCTION IN ADULT WOMEN

Consideration of the anatomy of the nervous system and events (ie., age, physical training, motor learning) that invoke changes in neural regulatory mechanisms and other bodily systems renders the impact of the type of instruction used to elicit a maximal effort in the assessment of muscle function across age, among different muscle groups, and for different parameters of muscle function tenuous. Hence, the efficacy and effect of using two types of instructions (rate vs. strength) on the assessment of the isometric functional capacity of six muscle groups were examined in women (N = 143) aged 25-74 years. The subjects were categorized by age into 10, 5-year groups. Measures of maximal force (MF), maximal rate of force increase (MR), total impulse (Tl), time to MF (MFT), time to MR (MRT), and plateau time (PLT, time between 90% MF and MF) were obtained from the force-time recordings of maximal voluntary isometric contractions of the finger flexors, thumb extensors, elbow flexors and extensors, and ankle dorsiflexors and plantar flexors. Repeated measures analyses of variance indicated that instruction type influenced (p < .05) the magnitude and pattern of the force-time recordings, with the degree of difference dependent upon the muscle group and parameter of muscle function examined. Use of the rate instruction yielded greater MRs (40.9-54 1.0 N/sec) than the strength instruction. The strength instruction elicited greater MFs (6.4-326.7 N), longer MFTs (0.72-1.50 sec), MRTs (0.05-0.15 sec) and PLTs (0.31-0.79 sec), and greater TIs (25.1-1,079.8 N-sec) than the rate instruction. An instruction that requires the subject to contract as fast as possible is recommended when rate parameters of muscle function are of interest; a test protocol that requests the subject to contract as hard as possible is recommended when the force parameters are assessed. Consideration of test protocol instruction is germane to obtaining accurate muscle function data. The use of two different instructions may provide more accurate and comprehensive isometric muscle function data than the traditional use of a single instruction.