Study Design: Repeated measures analysis o i joint angle e i i~t s on hip and k n w muscle cltrtromyographic IEMGI activitv. Objectives: To simultan~~usly determine angle-dependent changes in maximal voluntary isometric contraction IMVICI torque and EMG activity during hip extension and knee ilexion. Background: Procedures ior normalizing EMG data and ior determining torque-angle relationships for various joint motions both entail asking suhjects to exert an MVIC. The implicit assumption in t h r w paradigms is that magnitude of the EMG response is at a constant, m.iximum level so that ohservcd angle-tlepcndmt variations in torque are due to mechanical iactors, such as muscle length and muscle moment arm.Methods and Measures: Fifty suhjects (25 men and 25 women1 particip.itcd in this study (age, 23.5 + 4.6 y; range, 18-38 y). Subjects periormed maximal isometric knee ilexion at 4 kncv angles and maximal isometric h~p extension at 4 hip angles. The dependent variahlrr were nnrmalizrd root-mean-square EMG and torque. The process ior normalizing EMG and torque data consisted o i determining the largc3t mean value ior each suhject across tcrting positions for the muscle o i interest. That value was designated as corrcqmnding to 100% MVIC, and all other data ior that muscle were expressed as a percentage of the MVIC value. Repeated measures was used to determine angle-dependent changes in normalized MVICtorque and MVIC-EMG values ior each muscle group. Results: Mean torque-angle relationships were generally consistent with previous r e p m , though ~~n s i d e r d~l e intersuhject variability was observed. There were signiiicant .inglc-dependent diiierenccr in maximal EMG ior Ix)th the hamstring and gluteus maximus muscles. Worrell, Duke Universitv Medical Center, Deptartment oi Physical and Occupational Therapy PO 3965, Durham, NC 27710. E-mail: ~vorreOO6@mc.duke.edu xperimental approache.5 to the study of neuromuscular function frequently entail asking subjects to perform a maximal voluntary isornetric contraction (MVIC) of selected muscle groups. This approach is commonly used for amplitude normalization of electroinyographic (EMG) activity in order to determine the potential efficacv of various strengthening exercises by comparing the relative activity elicited by each e x e r c i~e . " . ' . ' .~"~ Maximal voluntary isometric contraction has also been used to determine in vivo torque-angle relationships of various joint motions by having subjects exert an MVIC at multiple points in the range of lnotion.~.~ t.21.22 The implicit assumption in these paradigms is that the instruction to perform an MVIC elicits a constant, rnaxi~nal level of motor iunit activity in the muscle of interest.The question of whether performance of an MVIC results in a
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