Postural synergies associated with a stepping task

Background and Purpose. Synergistic relationships among multiple muscle com ponents are thought to exist to simplify control of posture and movement. T he purpose of this study was to examine the extent to which children, young adults, and older adults exhibit consistent sequences of postural muscle a ctivation when lifting the right foot onto a step fr-om a standing position . Subjects. Twenty subjects without known impairments of the neuromuscular system (10 male, 10 female) in each of 3 age groups-children (8-12 years), young adults (25-35 years), and older adults (65-73 years)-participated, Me thods. ii pressure switch taped to the subject's right foot was used to det ermine movement onset and offset. Latencies of muscle activation were deter mined using surface electromyography. A preferred postural synergy was defi ned as the sequence of postural muscle activation observed during the major ity of trials for each subject. Results. Mean movement times did not differ among age groups. Although the left tibialis anterior (TA) muscle was the first of the postural muscles activated in 93% of the trials, subjects disp layed considerable variability in the subsequent order of postural muscle a ctivation. Across subjects, a total of 14 different preferred postural syne rgies were observed. Age groups did not differ in the number of different s ynergies. Conclusion and Discussion, Early TA activation may reflect biomec hanical constraints of the stepping task, producing forward displacement of the center of mass over the changing base of support. The fact that subjec ts of all ages were quite variable in the specific sequences of muscles act ivated subsequent to the TA suggests that, for this type of task, therapist s should not focus their interventions on facilitating execution of particu lar synergy patterns.