Motor unit number estimates and quantitative muscle strength measurements of distal muscles in patients with amyotrophic lateral sclerosis. Quantitative isometric muscle testing is one of the more frequent measures.
Muscle strength reflects the number of contributing muscle fibers.
Early in ALS, motor neuron loss will result in denervation, but weakness will be preserved by collateral reinnervation of orphaned muscle fibers. Strength will fall when there is continued motor unit loss and reinnervation can no longer keep up. Therefore, the relationship between denervation and strength is not linear. Serial MUNE studies have demonstrated an exponential loss of motor units even though there is a linear loss of strength. There are several methodological issues in their study that are worthy of comment.