Thigh and Shank, Kinetic and Potential Energies during Gait Swing Phase in Healthy Adults and Stroke Survivors.

Abstract

Background/Problem. Given the treatment-resistant gait deficits after stroke and known elevated energy cost of gait after stroke, it is important to study the patterns of mechanical energies of the lower limb segments. There is a dearth of information regarding mechanical energies specifically for the thigh and shank across the gait cycle. Therefore, the purpose of the current work was to characterize the following: (1) relative patterns of oscillation kinetic energy (KE) and potential energy (PE) within lower limb segments and across lower limb segments in healthy adults during the swing phase at chosen and slow gait speeds; (2) KE and PE swing phase patterns and values for stroke survivors versus healthy adults walking at slow speed; and (3) KE and PE patterns during the swing phase for two different compensatory gait strategies after stroke,. Methods. This was a gait characterization study, a two-group, parallel-cohort study of fourteen stroke survivors with gait deficits, walking at <0.4 m/s and eight adults with no gait deficits. For testing, the eight healthy adults walked at their chosen speed, and then at the imposed slow speed of <0.04 m/s. We used a standard motion capture system and calculation methods to acquire, calculate, and characterize oscillation patterns of KE and PE of the limb segments (thigh and shank) across the gait cycle. Results. In healthy adults, we identified key energy conservation mechanisms inherent in the interactions of KE and PE, both within the thigh and shank segments and across those limb segments, partially explaining the low cost of energy of the normal adult chosen speed gait pattern, and the underlying mechanism affording the known minimal set of activated muscles during walking, especially during the early swing phase. In contrast, KE was effectively absent for both healthy adults at imposed slow walking speed and stroke survivors at their very slow chosen speed, eliminating the normal conservation of energy between KE and PE within the thigh and across the thigh and shank. Moreover, and in comparison to healthy adult slow speed, stroke survivors exhibited greater abnormalities in mechanical energies patterns, reflected in either a compensatory stepping strategy (over-flexing the hip) or circumducting strategy (stiff-legged gait, with knee extended throughout the swing phase). Conclusions and contribution to the field. Taken together, these findings support targeted training to restore normal balance control and normal activation and de-activation coordination of hip, knee, and ankle muscles, respectively (agonist/antagonist at each joint), so as to eliminate the known post-stroke abnormal co-contractions; this motor training is critical in order to release the limb to swing normally in response to mechanical energies and afford the use of conservation of KE and PE energies within the thigh and across thigh and shank.