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