Changes in the recruitment threshold of motor units produced by cutaneous stimulation in man.

The effect of cutaneous stimulation on the recruitment of motor units has been studied during slowly increasing voluntary contractions of human first dorsal interosseous muscle. 2. Continuous electrical stimulation of the index finger at 4 x threshold for perception caused an increase in the recruitment threshold of units normally recruited at contraction strengths less than 1.5 N and a decrease in the recruitment threshold of units normally recruited at contraction strengths greater than 1.5 N. 3. It is concluded that the recruitment order of motor units during gradually increasing voluntary muscle contraction is not fixed but depends in part on cutaneous input.