Exteroceptive Suppression of Voluntary Activity in Thenar Muscles by Cutaneous Stimulation: How Many Trials Should Be Averaged?

Abstract Objective To determine a minimum number of trials that preserve input-output (I − O) properties of duration and magnitude of exteroceptive EMG suppression (eEMGs). Patients and Methods eEMGs was recorded in 16 healthy subjects from thenar muscles following index finger stimulation at 2.5, 5, 10, and 20 times sensory threshold (xST). Individual trials were rectified and incrementally averaged in blocks of 5, 10, 20, 30, 40, 50, and 60. To determine if the block size affects I − O properties, the goodness of curve fit parameter R2 for each block was compared to R2 of the global function across all blocks combined. Results eEMGs was found in all subjects at 10xST and 20xST (100%, respectively) but less often at 5xST (63-75%) and 2.5xST (25-56%). A quadratic function best described both duration and magnitude of eEMGs. The quadratic R2 did not significantly differ between any individual block function (5-60) and the global function (eEMGs duration 0.647-0.704 vs 0.679; magnitude 0.525-0.602 vs 0.560, respectively). Conclusions Averaging 5 trials consistently shows eEMGs at and above 10xST. I − O properties of eEMGs do not differ whether 5 or up to 60 trials are averaged. Clinical studies of eEMGs in thenar muscles are possible with as few as 5 trials averaged.