Measurement of isometric muscle strength: a reproducibility study of maximal voluntary contraction in normal subjects and amyotrophic lateral sclerosis patients

Amyotrophic lateral sclerosis (ALS) is a degenerative disease of unknown ca use, resulting in the progressive loss of voluntary motor activity. Traditi onal methods of evaluating patients with ALS (neurologic assessment, manual muscle testing and rating scales) involve subjective elements and lack the sensitivity needed to detect small but meaningful changes in deterioration and therapeutic efficacy. This paper presents a recently developed strengt h measurement instrument, useful for the long-term monitoring of muscle str ength deterioration in ALS. In addition, a reproducibility study to assess the intra- and interobserver reliability of maximal voluntary isometric con traction is reported. The strength measurement instrument consists of a str ain gauge force transducer, a bridge amplifier and a mechanical structure t o counteract movements. A personal computer acquires the strength signal du ring each voluntary contraction and automatically computes the maximal valu e. Reproducibility of measurement was assessed in 18 normal subjects tested twice, on successive days, with the same examiner and under the same condi tions. The interexaminer reproducibility of measurement was assessed in a g roup of 13 normal subjects and 10 ALS patients. Each subject of the two gro ups was independently examined by three examiners. The two reproducibility studies showed a high intraclass correlation coefficient (0.91-0.97) and lo w SEM and measurement error (3-10%) in all muscle regions tested. The Bland and Altman plots confirmed these results. (C) 2000 IPEM. Published by Else vier Science Ltd. All rights reserved.