Test--retest reliability of a modified multiple point stimulation technique for motor unit number estimation

Multiple point stimulation (MPS) is a widely used technique to estimate the number of motor units in a muscle. Test-retest reliability must be high for the motor unit number estimates to be clinically useful. We hypothesized that the reliability of MPS can be improved by using a long stimulus pulse width (1ms), in addition to the standard 0.05ms pulse width.

Median nerve innervated thenar muscles were examined in 11 young subjects, 27+/-3 (mean +/-SD) years old and in 5 elderly subjects, 71+/-11 years old. The experimenter conducted the studies twice on each subject.

Test-retest reliability, using the modified MPS technique, was substantially higher (Cronbach's alpha of 0.88) than using the standard method (Cronbach's alpha of 0.80) in the young subjects. In contrast, for the elderly subjects the test-retest reliability of MUNE was high for both the modified technique (Cronbach's alpha of 0.96) and the standard technique (Cronbach's alpha of 0.99).

Test-retest reliability of MPS can be significantly improved by using a long stimulus pulse width and the standard stimulus pulse width in younger subjects. However, this is not necessary in elderly subjects.

The greater reliability of this modified MPS method should enhance its clinical utility.