Normal range for H-reflex recording from the calf muscles

This study was performed to derive the normal range for H-reflex latency, recording from the calf, on a large and varied subject population. Two hundred fifty-one asymptomatic subjects without risk factors for neuropathy were tested bilaterally. The results were analyzed to determine whether various demographic characteristics were associated with different results. A repeated measures analysis of variance was performed with the latency as the dependent variable and age, race, gender, body mass index (kg/m2), and height as the independent variables. A significance value of P < or = 0.01 level was used. Side-to-side variability was also examined, and, for this measure, a repeated measurements analysis was not necessary because there was only one measurement per subject; a simple analysis of variance was used. Age and height were noted to be associated with different mean latencies; race, gender, and body mass index were not. The mean H-reflex latency was 30.3 +/- 2.4 ms, and the upper limits of normal (mean + 2 SD) for the various categories of age and height ranged from 30.0 to 38.2 ms. In addition, the upper limits of normal were derived as the 97th percentiles of observed latency values. For all subjects taken together, this value was 35.0 ms, and, for the various subgroups, it ranged from 29.7 to 36.4 ms. Mean side-to-side variability was 0.2 +/- 1.0 ms, with an upper limit of normal of 2.2 ms as the mean + 2 SD or 2.0 ms as the 97th percentile.