Themeasurementofmuscle strength inpatients with peripheral neuromuscular disorders

SUMMARY The variability of voluntary isometric strength measurements has been assessed innormal subjects and patients with peripheral neuromuscular disorders. Knee extensor strength was measured in a muscle testing chair 13 times over 5 monthsin each of six normal subjects:coefficients of variation (CV) ranged from 4-5 to 14-0% (mean 8.5%) for individual legs indifferent subjects. Paired measurements ofthe strength ofseveral clinically weakmuscle groupswere made 1-4 days apart in 20 patients using both a handheld dynamometer and the musclechair technique: the test/retest correlation was high (r = 0-97, p < 0.001). Visual biofeedbackdid not affect the strength recordedin most cases. Eachoffive patients had thestrength ofsix orseven clinically weakmuscle groups measuredbyfive examinerswithin a 24 hourperiod: the CV for the five examinersrangedfrom3-6-27.3% (mean 12-8%). A single examinermeasuring the samegroups on five occasionsinthreepatientsobtained amean CVof8-9%.Sources ofvariation