Postural synergies associated with a stepping task.
OBJECTIVE
Synergistic relationships among multiple muscle components are thought to exist to simplify control of posture and movement. The purpose of this study was to examine the extent to which children, young adults, and older adults exhibit consistent sequences of postural muscle activation when lifting the right foot onto a step from a standing position.


METHODS
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.


METHODS
A pressure switch taped to the subject's right foot was used to determine movement onset and offset. Latencies of muscle activation were determined using surface electromyography. A preferred postural synergy was defined as the sequence of postural muscle activation observed during the majority 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 displayed considerable variability in the subsequent order of postural muscle activation. Across subjects, a total of 14 different preferred postural synergies were observed. Age groups did not differ in the number of different synergies.


CONCLUSIONS
Early TA activation may reflect biomechanical constraints of the stepping task, producing forward displacement of the center of mass over the changing base of support. The fact that subjects of all ages were quite variable in the specific sequences of muscles activated subsequent to the TA suggests that, for this type of task, therapists should not focus their interventions on facilitating execution of particular synergy patterns.
Mercer
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Division of Physical Therapy, University of North Carolina at Chapel Hill 27599-7135, USA. vmercer@css.unc.edu
Sahrmann
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SA
D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D002648:Child; D004576:Electromyography; D005260:Female; D005528:Foot / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011930:Reaction Time; D015203:Reproducibility of Results; D018709:Statistics, Nonparametric