Elsevier

Journal of Biomechanics

Volume 58, 14 June 2017, Pages 212-216
Journal of Biomechanics

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Changes in relative work of the lower extremity joints and distal foot with walking speed

https://doi.org/10.1016/j.jbiomech.2017.04.012Get rights and content

Abstract

The modulation of walking speed results in adaptations to the lower limbs which can be quantified using mechanical work. A 6 degree-of-freedom (DOF) power analysis, which includes additional translations as compared to the 3 DOF (all rotational) approach, is a comprehensive approach for quantifying lower limb work during gait. The purpose of this study was to quantify the speed-related 6 DOF joint and distal foot work adaptations of all the lower extremity limb constituents (hip, knee, ankle, and distal foot) in healthy individuals. Relative constituent 6 DOF work, the amount of constituent work relative to absolute limb work, was calculated during the stance and swing phases of gait. Eight unimpaired adults walked on an instrumented split-belt treadmill at slow, moderate, and typical walking speeds (0.4, 0.6, and 0.8 statures/s, respectively). Using motion capture and force data, 6 DOF powers were calculated for each constituent. Contrary to previously published results, 6 DOF positive relative ankle work and negative relative distal foot work increased significantly with increased speed during stance phase (p < 0.05). Similar to previous rotational DOF results in the sagittal plane, negative relative ankle work decreased significantly with increased speed during stance phase (p < 0.05). Scientifically, these findings provide new insight into how healthy individuals adapt to increased walking speed and suggest limitations of the rotational DOF approach for quantifying limb work. Clinically, the data presented here for unimpaired limbs can be used to compare with speed-matched data from limbs with impairments.

Introduction

The effective modulation of walking speed results in adaptations by the lower limbs which can be quantified using various gait parameters. Recognizing that the flow of energy gives rise to movement, analyses to quantify lower limb adaptations with speed are ideally suited to use the principles of energy, work, and power.

Biomechanical joint work has historically been calculated using a sagittal (1 degree-of-freedom (DOF) rotational) or 3 DOF (all rotational) approach. Teixeira-Salmela, et al. calculated positive and negative joint work as a percentage of absolute sagittal limb work (summed positive and absolute negative work of the hip, knee, and ankle) over the entire gait cycle (Teixeira-Salmela et al., 2008). The researchers found the relative percent contribution of both positive and negative ankle work decreased with increased walking speed, while the hip and knee contributions increased, suggesting the hip flexor muscles assist with limb forward progression. These findings were consistent with relative joint work calculations over stance phase only (Chen et al., 1997). Farris and Sawicki used 3 DOF data to calculate the percent average positive joint power relative to the total average positive power of the limb over a stride (Farris and Sawicki, 2011) and found that positive relative joint average power did not differ across speeds.

Recently, Zelik et al. utilized a 6 DOF approach to determine changes in lower limb work with speed (Zelik et al., 2015a). The analysis used 6 DOF power calculations for the hip, knee, and ankle joints (Buczek et al., 1994) and the inclusion of a distal foot segmental power term (Siegel et al., 1996). (The term “constituent” will be used throughout this manuscript to refer to the hip, knee, and ankle joints and the distal foot segment.) A 6 DOF approach, which includes joint translations unlike the 3 DOF approach, is currently the most comprehensive means for analyzing the energy changes of the system. Summing the constituent work to generate a measure of 6 DOF limb work, Zelik et al. found that both positive and negative 6 DOF limb work increased with speed (Zelik et al., 2015a). However, it remains unclear if the relative constituent contributions to the absolute 6 DOF limb work adapt by increasing proportionally with walking speed.

We used 6 DOF work calculations of the four lower limb constituents to quantify the relative constituent work, or the percentage of positive or negative work each constituent contributed to absolute 6 DOF limb work, across a stride, revealing the primary constituent “drivers” and “brakers”, respectively. Work at the joint and segmental levels is defined here as a measure of energy generation (positive) and dissipation (negative) (e.g. by muscles). However, it is noted that inverse dynamics calculations of work do not account for co-contraction, work done by two-joint muscles, partition of energy stored in elastic structures versus muscle, or heat dissipation (Purkiss and Robertson, 2003, Umberger and Martin, 2007). Relative constituent work can be meaningful for characterizing how constituent contributions to gait change throughout the gait cycle and how these contributions are affected by speed. The objective of this study was to quantify the speed-related 6 DOF work adaptations of all the lower extremity limb constituents in healthy individuals.

Section snippets

Methods

A subset of previously reported data (Goldberg and Stanhope, 2013) was used for data analysis. Briefly, eight healthy adult subjects (height 1.77 ± 0.08 m, mass 71.8 ± 15.5 kg) walked on an instrumented treadmill (Model TM-06-B, Bertec Corp., Columbus, OH) while kinematic and force platform data were collected. All subjects provided informed consent under IRB protocol. Reflective markers were placed on subjects using a modification to a previously reported marker configuration (Holden et al., 1997)

Results

Power curves for each constituent are shown in Fig. 1. Absolute 6 DOF limb work over a gait cycle significantly increased with walking speed (p < 0.001): 0.93 ± 0.20 J/kg, 1.28 ± 0.25 J/kg, and 1.66 ± 0.31 J/kg for slow, moderate, and typical speeds, respectively (all p < 0.001). Average relative constituent work values with standard deviations are represented in bar charts in Fig. 2. Table 1 lists the means and standard deviations for relative constituent work values (J/kg) during stance and swing.

There

Discussion

The purpose of this study was to use 6 DOF calculations of work to identify lower limb constituent adaptations that occur with increased walking speed. In healthy individuals without lower limb impairments, constituent work relative to absolute limb work calculations identified that primarily the relative work contributions of the ankle and distal foot in stance change with increases in walking speed (Fig. 2).

Relative constituent work characterizes how constituent contributions to gait change

Conflict of interest

The authors have no financial or personal relationships with individuals or organizations that inappropriately influenced this work.

Acknowledgments

This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1247394 and by the University of Delaware College of Health Sciences and the Mechanical Engineering department. The authors would like to thank Tom Kepple for assistance with data analysis, and Dr. Ryan Pohlig for assistance with statistical analysis. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not

Glossary

Definition of terms

Adaptations
Changes or adjustments made by the lower limb and/or its constituents due to a change in gait intensity which in this case is increasing walking speed. Quantified by relative work.
Constituent work
The work done by a constituent (a joint or distal foot segment of the lower limb, i.e. hip, knee, ankle, distal foot). Modified by positive/negative/net/absolute; specified during a phase of gait (stance/swing). Notation: ModifierWconstituent
Limb work
The work done by a limb; calculated as

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