Methodology for determining the sensitivity of swing leg toe clearance and leg length to swing leg joint angles during gait

During the swing phase of gait, the effective length of the leg—distance from the hip joint center to the toe—must be made shorter than the distance from the hip to the floor to avoid toe-stubbing or tripping while walking. Critical toe clearance occurs approximately halfway through swing phase when the distance between the toe and the floor reaches a local minimum. Analytical techniques derived in this study were used to evaluate: (1) the sensitivity of toe clearance to the swing leg hip, knee, and ankle joint angles; and (2) the sensitivity of the hip–toe distance to the swing leg knee and ankle joint angles. The toe clearance, hip–toe distance, toe clearance sensitivity (TCS), and hip–toe distance sensitivity (HTDS) were calculated for each frame of data during the swing phase of 10 able-bodied subjects. A minimum toe clearance of 1.9 ± 0.5 cm occurred at about 51% of the swing phase during able-bodied gait. At that particular time, the toe clearance was found to be most sensitive to the angle of the ankle (17.1 cm/rad), then the hip (9.5 cm/rad), and lastly the knee (2.5 cm/rad). The hip–toe distance was found to be about twice as sensitive to the angle of the ankle (−15.3 cm/rad) than to that of the knee (−7.6 cm/rad) at the time of critical toe clearance. The methodology developed here and the baseline information calculated for able-bodied subjects could be used to evaluate the effects that different gait pathologies have on swing-phase toe clearance and hip–toe distance.