Electromyographic study of muscular overflow during precision handgrip.

This study was designed to describe the "overflow" of muscular activity to muscles beyond the essential prime mover and synergists during a precision handgrip exercise. Five subjects performed a 10-minute isometric handgrip exercise consisting of one-second contractions alternated with one-second rests. Four different force levels were assigned: 5, 15, 25, and 40 percent of each subject's maximum handgrip force. All subjects demonstrated overflow activity at the 5-percent level, and three of the five subjects showed more overflow at the 5-percent level than at 15 percent. The greatest amount of overflow was shown at the 40-percent level. No striking interindividual or intraindividual consistency in recruitment order of overflow muscles was apparent. Two distinguishable types of overflow were observed: continuous overflow was the characteristic type at the lower force levels, whereas an interrupted pattern of overflow synchronized to the handgrip contraction was typical of the higher force levels. The possible effects of overflow on precision motor skills are discussed.