ELECTROMYOGRAPHIC ACTIVATION AND PROPORTION OF FAST VERSUS SLOW-TWITCH MUSCLE-FIBERS - A GENETIC DISPOSITION FOR PSYCHOGENIC MUSCLE TENSION

17 right-handed males volunteered for an experiment that compared task -related patterns of electromyographic (EMG) activation with data from muscle biopsy on proportion of slow-twitch ((ST) aerobic) to fast-twi tch ((FT) anaerobic) muscle fibers. The biopsy was taken from the righ t-leg gastrocnemius muscle after EMG measurement from that area of the leg muscle. EMG was also recorded from the left forearm flexor carpi radialis area. Recordings were obtained from pre- and post-task restin g periods and during 150 s of video-task performance when the right ha nd operated a joy-stick. The results showed a highly significant tonic EMG activation in the leg muscle of subjects with predominance of ST fibers, and this relationship generalized to the EMG from the 'passive ' forearm. The proportion of ST to FT fibers is genetically defined an d not altered by exercise. Therefore, our results lend support to a ge netic differentiation between individuals with high vs. low probabilit y of unintended build-up of muscle tension during perceptual-motor tas k performance.