Amputee Step Activity is Correlated to Stride-to-Stride Fluctuations at the Ankle

The skilled performance of a complex movement, such as walking, is associated with an optimum level of variability that provides flexibility given an ever-changing environment [1]. Amputees reveal significantly increased stride-to-stride fluctuations during walking [2] indicative of a greater disorganisation of movement. Although such presentation is linked with pathology, it may also be related to decreased activity in this population. The purpose of this study was to determine the relationship between an amputee’s activity level and stride-to-stride fluctuations. Twenty-two transtibial amputees (51.9±10.8yrs, 1.77±0.80m, 100.9±19.3kg) consented to participate. Average daily step count (DSC) was computed over a 3 week period via a step activity monitor (Actigraph, Pensacola, FL, USA) attached to the prosthesis. Following this period, each subject walked on the treadmill at their self-selected speed while kinematics were recorded (60 Hz; 12- camera Motion Analysis Corp., Santa Rosa, CA, USA). Stride-to-stride fluctuations for the sound and prosthetic ankle motion were calculated with the largest Lyapunov exponent (LyE). Relationships between DSC and ankle LyE were tested through a Pearson correlation (α=0.05). A significant negative, moderate relationship with DSC was shown with the sound ankle LyE (r=- 0.569, p=0.006), however not with the prosthetic ankle LyE (r=-0.091, p=0.687). This significant negative correlation at the sound ankle demonstrates that decreased stride-to-stride fluctuations are associated with increased activity levels, however further work is necessary to resolve the type of relationship present. It remains unclear whether the disorganization promotes decreased activity or whether less active individuals do not gain sufficient motor learning experience to achieve a skilled movement.Stergiou et al. (2006) Journal of Neurologic Physical Therapy. 30(3):120-129. Wurdeman et al. (2013) Annals of Biomedical Engineering. 41(4):806-813