Reliability of motor-evoked potentials in the ADM muscle of older adults

The purpose of this study was to determine the reliability of motor-evoked potentials (MEPs) produced in the abductor digiti minimi (ADM) muscle of male and female older adults, both within and between sessions. The number of trials within a session required to obtain reliable results was also examined. The investigation was conducted on 30 elderly individuals (15 M, 15 F; mean age 76 years). With the ADM at rest, MEPs were evoked at intensities of 1.1, 1.3, and 1.5 times motor threshold (MT). Ten stimuli were delivered at each intensity, with 10-12 s between stimuli. The MEP responses were blocked with two, three, four, and five-stimuli means in each block. An intraclass correlation (ICC) reliability analysis of variance model was used to assess reliability of the MEP amplitude, using a variable number of trials per block. A subset of 10 subjects repeated the protocol following 20 min of rest to assess the reliability between sessions. As expected, MEP amplitudes were significantly higher as stimulus intensity increased. There were no significant differences between blocks, nor was there a significant gender effect. ICC reliability coefficients ranged between 0.09 with two trials per block and 0.97 with five trials per block. Between session reliability ranged from 0.65 to 0.83. Highly reliable MEP amplitudes can be obtained in older individuals using two blocks of TMS stimuli with five trials per block.