  Falls during walking are a major health issue in the elderly population.
Older individuals are usually more cautious, work more slowly, take shorter
steps, and exhibit increased step-to-step variability. They often have impaired
dynamic balance, which explains their increased falling risk. Those locomotor
characteristics might be the result of the neurological/musculoskeletal
degenerative processes typical of advanced age or of a decline that began
earlier in life. In order to help determine between the two possibilities, we
analyzed the relationship between age and gait features among 100 individuals
aged 20-69. Trunk acceleration was measured during 5-min treadmill session
using a 3D accelerometer. The following dependent variables were assessed:
preferred walking speed, walk ratio (step length normalized by step frequency),
gait instability (local dynamic stability, Lyapunov exponent method), and
acceleration variability (root mean square (RMS)). Using age as a predictor,
linear regressions were performed for each dependent variable. The results
indicated that walking speed, walk ratio and trunk acceleration variability
were not dependent on age (R2<2%). However, there was a significant quadratic
association between age and gait instability in the mediolateral direction
(R2=15%). We concluded that most of the typical gait features of older age do
not result from a slow evolution over the life course. On the other hand, gait
instability likely begins to increase at an accelerated rate as early as age
40-50. This finding support the premise that local dynamic stability is likely
a relevant early indicator of falling risk.
