Dependence of Muscle Energy Expenditure on Stride Rate in Walking

Abstract

0358 At nearly any walking speed, humans tend to use the stride rate that results in minimum whole-body energy expenditure. The contribution of lower-limb muscles to the total energy is unknown, but likely to be important in the selection of a walking stride rate. Furthermore, the factors that cause energy expenditure to vary with stride rate are not well understood. Greater insight regarding these issues might be gained by using predictive biomechanical models of human walking. PURPOSE: To investigate the dependence of lower limb muscle energy expenditure on stride rate during constant-speed walking using a musculoskeletal model. METHODS: Forward dynamic computer simulations of walking were generated using a planar, nine degree-of-freedom model of the skeletal system, which was actuated by 24 Hilltype muscle models. Simulations were generated at a typical preferred stride rate, plus stride rates 20% above (+20%) and below (−20%) preferred. Energy expenditure was predicted using a model of muscle heat and work production, and the energy expended by the head, arms, and trunk was estimated as well. Kinematic and kinetic data for the simulations were based on results from a prior study of 10 healthy subjects. Model energy expenditure was compared to metabolic data from these same subjects. RESULTS: Whole-body energy expenditure for the model was lowest at the preferred stride rate (4.79 W/kg) and elevated at the −20% (5.22 W/kg) and +20% (4.93 W/kg) stride rates. Model energy liberation was similar to experimental data across stride rates, and lower limb muscle energy expenditure followed the same minimization trend as global energy. Muscle energy expenditure was greater at the −20% stride rate than at the +20% stride rate, primarily due to a relatively higher cost of generating muscular force when taking long, slow strides. CONCLUSIONS: Based on model predictions, lower-limb muscle energy expenditure is minimized at the preferred stride rate. This may represent an important criterion that the nervous system uses in selecting a preferred walking pattern. Current work is focused on interrelationships between metabolic and mechanical energy minimization in walking. Supported by NSF IGERT grant DGE9987619. This work was completed in the Exercise & Sport Research Institute at Arizona State University in Tempe, AZ.