Comparison of maximal voluntary isometric contraction and Drachman's hand-held dynamometry in evaluating patients with amyotrophic lateral sclerosis

Maximal voluntary isometric contraction (MVIC) is a standard tool for assessment of muscle strength in treatment trials for amyotrophic lateral sclerosis (ALS). There is need for more practical bedside techniques especially for severely disabled patients. Hand-held dynamometry (HH-Dyn) is an inexpensive and easy-to-handle device. MVIC was measured in five proximal muscle groups bilaterally and compared with HH-Dyn in 43 ALS patients. After a training period we found good intrarater correlation for HH-Dyn (r = 0.99), with a low coefficient of variation. Measurements tended to become more accurate after repeated testing due to practice effects in examiners and patients. Overall correlation between HH-Dyn and MVIC was good r = 0.85 (P < 0.01). Strength-range-specific analysis showed a significant linear correlation up to 20 kg (44 lbs.) r = 0.57 (P < 0.01). However, we found a tendency to underestimate muscle strength above 10 kg by HH-Dyn as compared with MVIC, but this became meaningful only above a force of 20 kg. HH-Dyn provides a strength estimate with a precision close to MVIC in weak muscle groups (MRC grade 4). With standardization and appropriate training, HH-Dyn is a useful bedside test, providing an alternative to MVIC for follow-up assessment in ALS.