Control of Foot Trajectory in Human Locomotion: Role of Ground Contact Forces in Simulated Reduced Gravity

Abstract

We studied the changes of vertical contact forces, lower limb kinematics, and electromyographic activity (EMG) at different speeds and gravitational loads. To this end healthy subjects were asked to walk on a motorized treadmill while the percentage of body weight unloaded (body weight support, BWS) was modified in steps by means of a well-characterized unloading system. BWS was set at 0, 35, 50, 75, 95, or 100% of body weight. Walking speed was 0.7, 1.1, 2, 3, or 5 km/h. We found that changing BWS between 0 and 95% resulted in drastic changes of kinetic parameters but in limited changes of the kinematic coordination. In particular, the peak vertical contact forces decreased proportionally to BWS; at 95%-BWS they were 20-fold smaller than at 0% and were applied at the forefoot only. Also, there were considerable changes of the amplitude of EMG activity of all tested lower limb muscles and a complex re-organization of the pattern of activity of thigh muscles. By contrast, the corresponding variation of the parameters that describe shape and variability of the foot path was very limited, always <30% of the corresponding values at 0 BWS. Moreover, the planar co-variation of the elevation angles was obeyed at all speed and BWS values. Minimum variance of limb trajectory occurred at 3 km/h. At 100% BWS, subjects stepped in the air, their feet oscillating back and forth just above but never contacting the treadmill. In this case, step-to-step variability of foot path was much greater than at all other BWS levels but was restored to lower values when minimal surrogate contact forces were provided during the "stance" phase. The results did not depend on the specific instruction given to the subject. Therefore we conclude that minimal contact forces are sufficient for accurate foot trajectory control.

A novel approach to mechanical foot stimulation during human locomotion under body weight support

“…Foot-trajectory spatial variability in the sagittal plane was quantified in terms of normalized tolerance area of VM, computed over the swing phase (Ivanenko et al, 2002). Briefly, VM trajectories (relative to the mean position of GT) were re-sampled in the space domain by means of linear interpolation of the x, y time series (1.5-mm steps) over all gait cycles.…”

“…4B), nor did it affect the duration of the gait cycle (p > .5 in all cases), which was 1.37 ± 0.07 s, 1.45 ± 0.08 s, 1.60 ± 0.16 s, and 1.46 ± 0.24 s at 50%, 75%, 90%, and 100% BWS, respectively. In air-stepping, an extra foot pressure could evoke some limited changes in the shape of the foot trajectory (possibly, in part due to the small direct mechanical effect of pressure on the shoe volume), however, it did not increase (or decrease) foot path variability as one would have expected from application of surrogate contact forces (Ivanenko et al, 2002).…”

“…To imitate this general picture of temporal pressure distribution, the stimuli were applied separately to the heel and ball zones during the stance phase of each foot using the real-time kinematic feedback from horizontal foot motion. During walking at 3 km/h, the stance duration is about 850-900 ms and cycle duration is about 1.3-1.5 s (Ivanenko et al, 2002). To mimic the loading pattern, the heel insole was activated from 50 to 550 ms (trigger on and off signals, respectively) and the ball insole from 150 to 700 s (see Section 3).…”

“…Loss of cutaneous sensation may in fact lead to less stable posture and locomotion (Courtemanche et al, 1996;Dingwell & Cavanagh, 2001;Meyer, Oddsson, & De Luca, 2004;Perry, McIlroy, & Maki, 2000;Taylor, Menz, & Keenan, 2004) or affect the foot motion (Bouyer & Rossignol, 2003). In these processes, even minimal contact forces can be functionally critical (Ivanenko, Grasso, Macellari, & Lacquaniti, 2002;Jeka, Schöner, Dijkstra, Ribeiro, & Lackner, 1997). In addition, mechanical foot stimulation may attenuate muscle atrophy induced by prolonged hindlimb unloading (Kyparos, Feeback, Layne, Martinez, & Clarke, 2005) such as that induced in astronauts by prolonged exposure to microgravity, or may enhance voluntary contractions during exercises in leg muscles (Layne, Forth, Baxter, & Houser, 2005).…”

“…Thus, foot pressure stimulation can be used as an important gait-related sensory input during gait rehabilitation in combination with other methods or therapies. The tactile pressure input from the soles is attenuated and may vary significantly with body unloading (Flynn, Canavan, Chiang, & Cavanagh, 1997;Ivanenko et al, 2002) or when using gait machines enabling the repetitive foot motion (Dietz & Colombo, 2004;Hesse, Schmidt, & Werner, 2006). Several techniques have been previously proposed to increase or modify an input from the foot (Hijmans, Geertzen, Schokker, & Postema, 2007;Priplata, Niemi, Harry, Lipsitz, & Collins, 2003) such as step-synchronized vibration stimulation of soles (Novak & Novak, 2006;Priplata et al, 2006), ankle-foot orthosis (Gordon, Wu, Kahn, Dhaher, & Schmit, 2009), redistributing plantar pressure footwear (Bus, Waaijman, Arts, & Manning, 2009;Duranti, Galletti, & Pantaleo, 1985;Rao, Baumhauer, Becica, & Nawoczenski, 2009), mechanical support stimulation imitating walking in conditions of microgravity or prolonged hypokinesia (Chernikova, Umarova, Saenko, & Kozlovskaya, 2007;Sayenko, Miller, Ivanov, Galanov, & Guekht, 2005) or electrical stimulation of distal nerves.…”