Effects of step length and step frequency on lower-limb muscle function in human gait
Introduction
Humans walk at different speeds by varying their step length and step frequency independently. The product of these two variables determines walking speed. Previous studies have investigated the effects of step length and step frequency on walking biomechanics by comparing the gait patterns of older adults against those of healthy controls. Kerrigan et al., 1998, Judge et al., 1996, Elble et al., 1991, and Winter et al. (1990) found that older adults walk more slowly than healthy controls by reducing their step length rather than step frequency. Older adults also walk with reduced peak hip extension angles (Kerrigan et al., 1998), decreased range of motion at the knee (Judge et al., 1996), smaller peak ankle plantarflexion angles (Judge et al., 1996, Kerrigan et al., 1998), and reduced peak hip-extension, knee-extension and ankle-plantarflexion moments (Judge et al., 1996, Kerrigan et al., 1998). Whilst these differences in joint kinematics and kinetics between young and older adults suggest that step length may have a greater effect on muscle function than step frequency, the results are confounded by the effect of age. Investigating a single cohort of healthy young adults would address this concern as it would more clearly delineate the separate effects of step length and step frequency on gait biomechanics and lower-limb muscle function.
The influence of walking speed on muscle-fiber lengths and muscle contributions to the ground reaction force in healthy young adults has been investigated using musculoskeletal modeling techniques. Arnold et al. (2013) found that a change in walking speed affects the region of the force-length curve on which the ankle plantarflexors operate, while the functional performance of the other lower-limb muscles appear to be less affected by walking speed. Previous studies also have shown that five muscles - gluteus maximus (GMAX), gluteus medius (GMED), vasti (VAS), gastrocnemius (GAS) and soleus (SOL) - contribute most substantially to the vertical and fore-aft components of the ground reaction force across a wide range of walking speeds (Jansen et al., 2013, John et al., 2012, Liu et al., 2008, Pandy and Andriacchi, 2010, Pandy et al., 2010). The results of these studies suggest that walking speed affects the magnitudes of the muscles’ contributions to vertical support and forward progression more than their timing or coordination (Pandy and Andriacchi, 2010). No study to our knowledge has examined the separate effects of step length and step frequency on lower-limb muscle function during gait, specifically, the contributions of individual muscles to the vertical and fore-aft components of the ground reaction force and the region of the force-length relationship on which an individual muscle operates.
The aim of the present study was to quantify the separate effects of step length and step frequency on lower-limb muscle function during walking in healthy young adults. Three-dimensional gait data were used in conjunction with musculoskeletal computer modeling to evaluate muscle function as participants walked at a wide range of speeds using prescribed combinations of step length and step frequency. We evaluated the individual contributions of the major hip, knee and ankle extensors, specifically, GMAX, GMED, VAS, SOL and GAS, to vertical support and forward progression as step length and step frequency were changed independently. We hypothesized that muscle function would be more greatly affected by changes in step length than step frequency.
Section snippets
Methods
Ten healthy young adults (age, 24.2 ± 2.7 years; height, 169.7 ± 9.3 cm; mass, 67.7 ± 10.5 kg; BMI, 23.5 ± 2.6 kg/m2) were recruited to this study. Each participant provided written informed consent after approval was obtained from the University’s Human Research Ethics Committee. All participants walked unassisted and were free from any pathology that could influence their ability to ambulate normally.
Gait experiments were conducted in the Biomotion Laboratory at the University of Melbourne. Each
Results
Sagittal plane joint motion correlated significantly with changes in step length and step frequency at all walking speeds (R > 0.5; p < 0.05) (Fig. 2). Peak hip flexion, hip extension and knee flexion angles correlated more closely with changes in step length (Hip flexion: Coef = 6.54; Hip extension: Coef = 5.71; Knee flexion: Coef = 6.61) than step frequency (Hip flexion: Coef = 0.18; Hip extension: Coef = −0.17; Knee flexion: Coef = 2.94). Peak hip extension, hip flexion, knee extension and ankle
Discussion
We examined the separate effects of step length and step frequency on the individual contributions of the lower-limb muscles to vertical support and forward progression for a wide range of walking speeds in healthy young adults. We found that the same five muscles – GMAX, GMED, VAS, GAS, and SOL – dominated vertical support and forward progression independent of changes made to either step length or step frequency and that, overall, changes in step length had a greater effect on lower-limb
Conflict of interest
The authors do not have any financial or personal relationships with other people or organizations that could inappropriately influence this manuscript.
Acknowledgments
This work was supported by a Discovery Projects Grant from the Australian Research Council (DP160104366) and an Innovation Fellowship from the Victorian Endowment for Science, Knowledge and Innovation awarded to MGP.
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