Exploring phase dependent functional gait variability.

Gait variability is frequently used to evaluate the sensorimotor system and elderly fallers compared to non-fallers exhibit an altered variability in gait parameters during unchanged conditions. While gait variability is often interpreted as movement error, it is also necessary to change the gait pattern in order to react to internal and external perturbations. This phenomenon has been described as functional variability and ensures the stability of gait motor control. The aim of the current study is to explore the functional variability in relation to the different phases of the gait cycle (phase-dependent gait variability). Kinematics of the foot, shank and thigh were registered with inertial sensors (MTw2, Xsens Technologies B.V) in 25 older participants (70±6years) during normal overground walking. Phase-dependent variability was defined as the standard deviation of the Euclidean norm of the angular velocity data. To assess differences with respect to the variability of different body segments (foot, shank, and thigh), the statistical parametric mapping method was applied. In normal walking, the variability of the time-continuous foot kinematics during parts of the swing phase was higher compared to the shank (9-14% of swing phase, p<0.000) and to the thigh (3-43%, p<0.000 and 92%, p=0.024 of swing phase). Compared to the thigh, the shank kinematics was less variable at 62-64% (p=0.013) of the swing phase. The magnitudes of the variability were comparable regarding all three body segments during mid swing. Furthermore, those magnitudes of variability were smallest during mid swing where the minimum toe clearance was identified. In conclusion, we found signs of phase-dependent functional variability particularly in the swing phase of gait. In fact, we found reduced variability in the time-continuous foot kinematics in mid swing during normal walking where also the minimum toe clearance event occurs.