Age-related changes in the initiation of gait: Degradation of central mechanisms for momentum generation

Objective: To investigate cross-sectionally age-related changes in the expr ession and biomechanical efficiency of the gait-initiation motor program. Design: Case-control study. Participants and Setting: Twenty healthy young research subjects and 20 hea lthy elderly subjects who volunteered from the community participated in th is study at a university research laboratory. Main Outcome Measures: Participants performed gait-initiation trials at thr ee speeds from a starting position on a force platform while ground reactio n force data, 3-D motion analysis data, and electromyographic data were col lected. Measures included: latency of tibialis anterior (TA) activation and soleus (SOL) and gastrocnemius (GA) inhibition, magnitude of center of pre ssure (COP) displacement, magnitude of momentum generated, and final walkin g velocity. Results: The expression of the central motor program governing gait initiat ion, as evidenced by the invariant timing between TA activation and SOL/GA inhibition, was seen in both the young and elderly populations, but the fre quency was diminished in the latter group. The momentum-generating capacity of the COP shift mechanism was present but significantly diminished in the elderly population. Conclusions: These findings suggest that the central nervous system uses st able, efficient mechanisms for dealing with the inherent instability of upr ight bipedalism and that the integrity of these mechanisms degrades with ag ing. (C) 1998 by the American Congress of Rehabilitation Medicine and the A merican Academy of Physical Medicine and Rehabilitation.