The role of lower extremity joint powers in successful stair ambulation.

Ascending stairs is an important functional activity that is affected by lower extremity pathology including amputation. Although several studies have demonstrated stair ascent is more challenging than level ground walking, our understanding of the mechanics remains limited. The purpose of this study was to determine the association between lower extremity joint power generation and vertical COM acceleration (COM(A)) during stair ascent. Twenty-two healthy individuals underwent a biomechanical gait assessment while walking up a 16-step instrumented staircase. The association between the peak joint powers and peak COM(A) during stance were assessed with respect to timing and magnitude. With respect to timing, peak ankle joint power was highly correlated with peak COM(A) (R(2)=0.93), while peak knee and hip joint powers demonstrated limited association with COM(A) (R(2)=0.41 and 0.08, respectively). Only the magnitude of peak ankle power was associated with peak COM(A) (R(2)=0.3). Significant temporal and magnitude associations between peak ankle joint power and peak COM(A) suggest ankle power is a key contributor to COM(A). Although peak knee joint power and COM(A) are temporally associated, the association is weaker and the occurrence of peak joint knee power is nearly 10% after peak COM(A), suggesting knee joint power plays a lesser role in COM(A). These combined findings indicate the role of trail limb ankle plantarflexors should be recognized in the stair ascent cycle definition and demonstrate the potential importance of a power generated by the ankle plantarflexors to normalize stair ascent performance following lower extremity amputation.