Motor evoked potential response latencies demonstrate moderate correlations with height and limb length in healthy...

The purposes of this study were to determine 1) if motor evoked potential (MEP) response latencies and central motor conduction time (CMCT) are significantly correlated with lower extremity (LE) length or height, and 2) determine if MEP response latencies and CMCT are different between sexes among healthy adults. A cross-sectional, descriptive laboratory design was used. MEPs were recorded from 106 subjects (60 females, 46 males; age 20.1 +/- 2.4 years) by applying transcranial magnetic stimulation over the primary motor cortex. MEP response latencies were recorded using electromyography (EMG) responses from the tibialis anterior; CMCT was calculated from cortical and spinal-evoked MEP latencies. MEP latencies were significantly different between males (29.53 +/- 3.02 msec) and females (27.69 +/- 2.81 msec). Height accounted for greater variability (eta2 = .369 or approximately 37%) between genders and demonstrated a good-to-moderate correlation with MEP latency (r = .595, p = < .0001). Accounting for height as a confounding variable in the analyses, no significant differences between genders was observed (F1,103 = 2.45, p = .21). MEP latency should be adjusted to each subjects' height to account for the unwanted variability associated with the varied heights of subjects being tested, thereby permitting an accurate comparison and meaningful interpretation of MEPs between subjects or patients.