Internal consistencies of the delayed trunk muscle reaction times following a treadmill-induced slip perturbation while holding and not holding a tray.

Background: Reaction time task performance using electromyography (EMG) has been widely studied in the evaluation of motor responses. However, specific testing conditions with tray usage and the reliability of the bilateral trunk muscle reactions have not been proven.

Research Questions: Are there internal consistencies of the reaction times for a particular condition, such as a handheld task, among the examiners? Is there a delayed reaction time on the dominant abdominal muscle in response to a treadmill-induced slip perturbation while holding or not holding a tray?

Methods: One hundred and nineteen right upper and lower limb dominant individuals (71 female and 48 male subjects) were exposed to a treadmill-induced slip perturbation (0.24 m/s velocity for 1.2 cm) for 0.10 s in standing. The EMG electrodes were placed on both sides of the rectus abdominis (RA) and erector spinae (ES) muscles. The reliability of the test was established by using Cronbach's alpha, intra-class correlation coefficients (ICC), and the standard error of measurements.

Results: The results for holding a tray indicated a high degree of consistency based on Cronbach's alpha for the left RA (0.79), right RA (0.86), left ES (0.82), and right ES (0.73) muscles. However, there was a significant reaction time difference among trunk muscles (F = 10.58, p = 0.002) while not holding a tray. The post-hoc results indicated that the right RA muscle was delayed more than the bilateral ES muscles, although there was no significant difference with the left RA muscle.

Significance: Overall, the EMG analyses for the reaction times were highly consistent with and without tray usage. The reaction times of the dominant abdominal muscles were delayed while not holding a tray. Given the high reliability, compensatory strategies by trunk dominance might be considered with a tray usage task.