Contributions of muscles to mediolateral ground reaction force over a range of walking speeds

Abstract

Impaired control of mediolateral body motion during walking is an important health concern. Developing treatments to improve mediolateral control is challenging, partly because the mechanisms by which muscles modulate mediolateral ground reaction force (and thereby modulate mediolateral acceleration of the body mass center) during unimpaired walking are poorly understood. To investigate this, we examined mediolateral ground reaction forces in eight unimpaired subjects walking at four speeds and determined the contributions of muscles, gravity, and velocity-related forces to the mediolateral ground reaction force by analyzing muscle-driven simulations of these subjects. During early stance (0-6% gait cycle), peak ground reaction force on the leading foot was directed laterally and increased significantly (p<0.05) with walking speed. During early single support (14-30% gait cycle), peak ground reaction force on the stance foot was directed medially and increased significantly (p<0.01) with speed. Muscles accounted for more than 92% of the mediolateral ground reaction force over all walking speeds, whereas gravity and velocity-related forces made relatively small contributions. Muscles coordinate mediolateral acceleration via an interplay between the medial ground reaction force contributed by the abductors and the lateral ground reaction forces contributed by the knee extensors, plantarflexors, and adductors. Our findings show how muscles that contribute to forward progression and body-weight support also modulate mediolateral acceleration of the body mass center while weight is transferred from one leg to another during double support.

Figure 1

This study examines the mediolateral component of the ground reaction force during three periods: early stance, early single support, and late stance. The images show the direction of the peak mediolateral ground reaction force during each period.

Figure 2

Mediolateral component of ground reaction force as a percentage of body weight at four walking speeds, averaged over eight unimpaired subjects. The left panel shows a brief laterally directed ground reaction force in early stance followed by a medially directed ground reaction force. The right panel shows the peak ground reaction forces during three time periods (0-6%, 14-30%, and 40-56% gait cycle). Error bars span ± one standard deviation. Arrow indicates significant effect of speed on mediolateral ground reaction force.

Figure 3

Total mediolateral ground reaction force as a percentage of body weight and contributions to mediolateral ground reaction force from muscles, gravity, and velocity-related forces, averaged over the free-speed trials of all eight unimpaired subjects.

Figure 4

Peak contributions of major muscle groups to mediolateral ground reaction force, as a percentage of body weight, at four walking speeds during (A) 0-6%, (B) 14-30%, and (C) 40-56% gait cycle. Peak contributions for each speed were determined after averaging contributions across all eight unimpaired subjects. Error bars span ± one standard deviation. Arrow indicates significant effect of speed on contribution. Table 1 lists the muscles indicated by each abbreviation. “Contra” indicates muscles on the contralateral limb; all other muscles are on the ipsilateral limb.

Figure 5

Muscle groups modulating mediolateral ground reaction forces to transfer weight from the right leg to the left leg during double support. (A) The abductors on the right leg act with the hamstrings, vasti, adductors, and gluteus maximus on the left leg to generate leftward ground reaction forces. (B) The plantarflexors and adductors on the right leg, along with the abductors on the left leg, generate rightward ground reaction forces.

Figure 6

Mediolateral ground reaction force, as a percentage of body weight, averaged over 80 subjects drawn from Schwartz et al. (2008) at four walking speeds. * indicates significant difference (p < 0.05) between speeds. In early stance, peak lateral ground reaction force increased significantly with speed (very slow to slow, very slow to free). In early single support, peak medial ground reaction force increased significantly with speed (very slow to free, slow to fast). In late stance, peak medial ground reaction force decreased significantly with speed (slow to fast, free to fast).