Elsevier

Gait & Posture

Volume 8, Issue 3, December 1998, Pages 186-204
Gait & Posture

Increasing obstacle height and decreasing toe-obstacle distance affect the joint moments of the stance limb differently when stepping over an obstacle

https://doi.org/10.1016/S0966-6362(98)00034-4Get rights and content

Abstract

Foot placement during gait is important in regulating the dynamics of the joints of the supporting limb and in maintaining balance of the whole body. We hypothesized that increasing obstacle height and decreasing toe-obstacle distance (distance between the trailing foot and the obstacle during stance of the trailing foot just prior to stepping over the obstacle) would affect the joint moments of the stance limb differently when stepping over an obstacle. A total of 14 healthy young adults stepped over an obstacle 51, 102, 153, and 204 mm in height in a self-selected manner (i.e. toe-obstacle distance was not controlled) and for toe-obstacle distance targets of 10, 20, 30, and 40% of their step lengths measured during unobstructed gait. The adduction and internal rotation moments at the ankle joint increased as toe-obstacle distance decreased. The adduction and internal rotation moments at the hip joint during early stance, the internal rotation moment at the knee joint during late stance, and the dorsiflexion moment at the ankle joint during late stance increased with obstacle height. Reductions in toe-obstacle distance had greater effects on the moments of the ankle joint, and increases in obstacle height had greater effects on the moments of the hip joint. These greater demands on joint moments may affect the abilities of those elderly having decreased muscle strengths to safely step over obstacles.

Introduction

Tripping over obstacles is the most frequently mentioned cause of falls in the elderly 1, 2, 3, 4, 5. Studies have been performed to investigate the effects of obstacle height on the motions of the leading and trailing limbs 6, 7, 8, 9and on the joint moments of the stance limb 7, 8when stepping over obstacles in a self-selected manner. Larger joint motions and moments were found when stepping over a higher obstacle.

When stepping over obstacles of various heights in a self-selected manner both young and elderly adults were found to consistently place their trailing feet at approximately the same distance from the obstacle just before stepping over it 6, 10. This suggests that the location of foot placement relative to the obstacle is precisely controlled by the central nervous system in order to ensure a safe crossing. When toe-obstacle distance is self-selected, the distance between the trailing foot (stance limb) and the obstacle during stance of the crossing stride is 42–44%, ≈30 cm, of the step length measured during unobstructed level walking [10]. This distance allows the shank to move anteriorly and the ankle to dorsiflex as the body moves forward. When toe-obstacle distance is reduced, anterior motion of the shank and, therefore, dorsiflexion of the ankle would be expected to be limited by the closer proximity of the obstacle to the shank. The altered motion would be expected to alter the line of action of the weight of the body about the joints of the trailing limb, thereby affecting the moments about these joints. In support of this, obstacle proximity has been reported to affect maximum flexion of the hip and ankle during swing and mechanical power at the hip and knee during late stance [11]. Furthermore, in our most recent study of obstacle crossing [12]in which toe-obstacle distance was controlled, we found that stride length increased linearly as obstacle height increased and decreased linearly as toe-obstacle distance decreased. Thus, increases in obstacle height resulted in different geometrical configurations of the trailing limb than did decreases in toe-obstacle distance when the toe was over the obstacle. Therefore, the hypothesis of the present study was that when stepping over an obstacle decreases in toe-obstacle distance would affect the moments of the joints of the stance limb (trailing limb) differently than would increases in obstacle height. The information gained would be useful in enhancing our knowledge of the demands on the muscles of the lower extremities when stepping over obstacles.

Section snippets

Methods

Gait analysis was performed on 14 healthy young adults (seven males, seven females) having a mean age of 23 years (range, 19–32 years). Their average height was 171 cm (range, 158–184 cm), and their average weight was 694 N (range, 516–953 N). All but one of the subjects were right-hand dominant. The protocol for this study was approved by the Institutional Review Board of the University of Chicago. The experimental procedures for the study were explained to the subjects and informed consent

Results

Among the 16 moment variables investigated, five were significantly affected by toe-obstacle distance. At the ankle joint, the maximum adduction and internal rotation moments increased linearly (P≤0.022) during late stance as toe-obstacle distance decreased (Table 1, Fig. 2). Also, the maximum plantarflexion moment at the ankle joint during early stance decreased linearly (P=0.0003) as toe-obstacle distance decreased. At the knee joint, the maximum flexion moment during late stance decreased

Discussion

We reported previously that stride length increased linearly as obstacle height increased and decreased linearly as toe-obstacle distance decreased [12]. Therefore, increases in obstacle height resulted in different geometrical configurations of the trailing limb than did decreases in toe-obstacle distance when the toe was over the obstacle. Such geometrical changes would be expected to affect the moments about the joints of the stance limb. Thus, the hypothesis of the present study was that

Acknowledgements

We are grateful to Gary Piotrowski for his assistance in testing the subjects.

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    Present address: Orthopedic Biomechanics Laboratory, Department of Orthopedic, Mayo Clinic, Rochester, MN 55905, USA. E-mail: [email protected]

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