Original article
Metabolic and Mechanical Energy Costs of Reducing Vertical Center of Mass Movement During Gait

https://doi.org/10.1016/j.apmr.2008.07.014Get rights and content

Abstract

Gordon KE, Ferris DP, Kuo AD. Metabolic and mechanical energy costs of reducing vertical center of mass movement during gait.

Objectives

To test the hypothesis that reducing vertical center of mass (COM) displacement will lower the metabolic cost of human walking. To examine changes in joint work associated with increasing and decreasing vertical COM movement during gait.

Design

Randomized repeated measures.

Setting

Human Neuromechanics Laboratory, University of Michigan.

Participants

Able-bodied subjects (N=10).

Interventions

Subjects walked at 1.2m/s on a treadmill and overground. Subjects manipulated vertical COM displacement either by adjusting stride length or by using visual feedback to reduce COM movement.

Main Outcome Measures

We measured kinematic and kinetic data to calculate vertical and lateral COM displacements, joint torques, and work. In addition, we collected oxygen consumption to calculated metabolic power.

Results

Increasing and decreasing vertical COM displacement beyond subjects' preferred range resulted in increases in the metabolic cost of walking. When vertical COM displacement was reduced, corresponding increases in positive ankle and hip work and negative knee work were observed.

Conclusions

Humans are capable of walking in a manner that will reduce COM displacement from normal. Decreasing vertical COM movement results in increases in metabolic energy costs because of greater mechanical work performed at the hip, knee, and ankle joints. Thus, reducing vertical COM movement is not a successful strategy for improving either metabolic or mechanical energy economy during normal walking by able-bodied subjects.

Section snippets

Methods

We examined COM displacement, metabolic energy cost, and mechanical work performed at each joint during normal walking by able-bodied subjects. Vertical COM displacement was experimentally manipulated, first with visual feedback and second by control of stride length, and then compared against energy expenditure. We also performed inverse dynamic calculations to determine the work performed at each joint and the means by which subjects accomplished smooth walking.

Center of Mass Displacement

There was no difference between the force plate and segmental analysis methods for calculating vertical COM displacement at any of the 5 walking conditions (Holm-Sidak multiple comparison, P>.05). The single sacral marker method of calculating vertical COM displacement was different from the other 2 estimation methods during the 0.6, 1.0, and 1.2 PSL conditions (Holm-Sidak multiple comparison, P<.05). However, for the VFB condition, during which subjects used VFB about the sacral marker

Discussion

We sought to test whether reducing the vertical displacement of the COM improves walking economy in able-bodied subjects. Our results show that reduced COM displacement is not advantageous for either metabolic energy economy or the reduction of mechanical work at the joints. Energy expenditure increased whether subjects walked with shorter strides or by using VFB to reduce COM motion. The latter results agree with previous reports,5, 6 which are augmented here by the analysis of joint mechanics

Conclusions

The data reported here and elsewhere5, 6 do not support the hypothesis that it is energetically optimal to reduce COM displacement. Other studies31, 32, 33, 34, 35 also question whether several of the determinants actually contribute significantly to reducing COM displacement. Our data do indicate that substantial energy is expended for “production of rhythmic oscillations of the legs,”1(p553) but there is little evidence that it is “divided approximately equally” with other costs. This study

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      Consequently, the authors suggested that treatment planning should be informed by directly assessing energy expenditure rather than using gait kinematics and kinetics as predictors. Alternatively, Gordon et al. (2009) demonstrated that the metabolic demands of walking depend in part on work performed on the vertical displacement of the center of mass (COM). Further, Kurz et al. (2010) and Ries and Schwartz (2018) demonstrated that children with CP have a diminished ability to perform work to redirect the COM and are substantially less efficient at converting metabolic energy to COM work.

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