# Metabolic cost and mechanical work of walking in a virtual reality emulator

## TL;DR

This study compares the energy and mechanical effort of walking on a virtual reality treadmill versus normal walking, finding it requires more energy and changes movement patterns.

## Contribution

The study introduces a novel analysis of metabolic and mechanical aspects of walking on a multidirectional treadmill for virtual reality.

## Key findings

- Walking on the treadmill had higher metabolic cost than normal walking, running, and skipping.
- Mechanical work was similar to normal walking at higher speeds but less efficient due to sliding friction.
- Participants adopted different kinematics, including a forward-leaning posture and higher ankle dorsiflexion.

## Abstract

The purpose of this study was to investigate the metabolic cost (C), mechanical work, and kinematics of walking on a multidirectional treadmill designed for locomotion in virtual reality.

Ten participants (5 females, body mass 67.2 ± 8.1 kg, height 1.71 ± 0.07 m, age 23.6 ± 1.9 years, mean ± SD) walked on a Virtuix Omni multidirectional treadmill at four imposed stride frequencies: 0.70, 0.85, 1.00, and 1.15 Hz. A portable metabolic system measured oxygen uptake, enabling calculation of C and the metabolic equivalent of task (MET). Gait kinematics and external, internal, and total mechanical work (WTOT) were calculated by an optoelectronic system. Efficiency was calculated either as WTOT/C or by summing WTOT to the work against sliding frictions. Results were compared with normal walking, running, and skipping.

C was higher for walking on the multidirectional treadmill than for normal walking, running, and skipping, and decreased with speed (best-fit equation: C = 20.2–27.5·speed + 15.8·speed2); the average MET was 4.6 ± 1.4. Mechanical work was higher at lower speeds, but similar to that of normal walking at higher speeds, with lower pendular energy recovery and efficiency; differences in efficiency were explained by the additional work against sliding frictions. At paired speeds, participants showed a more forward-leaned trunk and higher ankle dorsiflexion, stride frequency, and duty factor than normal walking.

Walking on a multidirectional treadmill requires a higher metabolic cost and different mechanical work and kinematics than normal walking. This raises questions on its use for gait rehabilitation but highlights its potential for high-intensity exercise and physical activity promotion.

The online version contains supplementary material available at 10.1007/s00421-023-05306-0.