ORGANIZATION OF A SIMPLE 2-JOINT SYNERGY IN INDIVIDUALS WITH DOWN-SYNDROME

Subjects with Down syndrome and age- and gender-matched control subjec ts performed discrete elbow or wrist, flexion or extension movements i n a sagittal plane, moving one of the joints as fast as possible. The hand was either pronated or supinated. In control subjects, alternatin g bursts of activity were seen in the agonist-antagonist muscle pair c ontrolling the nonfocal joint. Subjects with Down syndrome, in most se ries, demonstrated simultaneous bursts of activity in the flexor and e xtensor muscles controlling both joints. This group difference was par ticularly pronounced for the muscles controlling the nonfocal joint. W e assume that the central nervous system may use two strategies to avo id flapping of a postural joint. The more universal co-contraction str ategy in Down syndrome may be viewed as an adaptive feature reflecting a general tendency of these persons to trade efficacy for safety.