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 expression and biomechanical efficiency of the gait-initiation motor program. Design: Case-control study. Participants and Setting: Twenty healthy young research subjects and 20 healthy elderly subjects who volunteered from the community participated in this study at a university research laboratory. Main Outcome Measures: Participants performed gait-initiation trials at three speeds from a starting position on a force platform while ground reaction force data, 3-D motion analysis data, and electromyographic data were collected. Measures included: latency of tibialis anterior (TA) activation and soleus (SOL) and gastrocnemius (GA) inhibition, magnitude of center of pressure (COP) displacement, magnitude of momentum generated, and final walking velocity. Results: The expression of the central motor program governing gait initiation, as evidenced by the invariant timing between TA activation and SOL/GA inhibition, was seen in both the young and elderly populations, but the frequency 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 stable, efficient mechanisms for dealing with the inherent instability of upright bipedalism and that the integrity of these mechanisms degrades with aging. (C) 1998 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.