# On the estimation of total muscle work done in human walking

## TL;DR

This study explores how muscle work during walking relates to metabolic rate, finding that total muscle power better predicts energy use than external work alone.

## Contribution

The study introduces a new method to estimate total muscle power during walking by combining external and internal work components.

## Key findings

- Total muscle power (Ptot) has a strong relationship with metabolic rate (R2=0.972) across various walking conditions.
- The Ptot–MR relationship resembles that of cycling, suggesting a unified principle for energy expenditure.
- Walking speed's influence on the Ptot–MR relationship is nearly eliminated, unlike in external work alone.

## Abstract

In many whole-body exercise forms, e.g. cycling, the relationship between metabolic rate (MR) and mechanical power output during exercise is linear and unique. Such linearity is not seen for walking. We investigated whether total muscle power (Ptot), i.e. power required for the inverted pendulum motion in walking plus power against net external resistance, demonstrated such a single relationship between Ptot and MR, independent of walking conditions. We studied walking under conditions in which considerable net external work against the environment was done (walking uphill and when resistive forces are imposed) as well as on the level, i.e. without net external work done. Fifteen adults walked freely on a large treadmill at 27 combinations of three speeds (3, 4.5 and 6 kmh−1), three inclines (0%, 3% and 6%) and three resistive forces (0.1×9.81, 2.5×9.81 and 5×9.81 N). Kinematics were recorded by motion capturing. MR was estimated from gas exchange recordings. Required Ptot generated by skeletal muscle was estimated as the power associated with step-to-step transitions (Psst) in addition to net external power (Pext), with Ptot=Pext+Psst. The Pext–MR relationship was not entirely unique (R2=0.883) and was strongly affected by speed (P=0.004). The Ptot–MR relationship was stronger (R2=0.972) and the influence of walking speed was almost cancelled out. The Ptot–MR relationship resembles that found for cycling. On that basis, we conclude that Ptot seems to incorporate the major amount of work done during walking.

Summary: A model explaining work done by skeletal muscle in walking indicates that work against environmental forces and work required for the inverted pendulum motion determine required work during walking.