Economical estimates of oxygen uptake as a function of gait parameters for an ambulatory monitoring systems

To examine a method to save time and money with empirical equations representing the relationship between oxygen uptake (VO₂), walking speed (v), step frequency (SF), and step length (SL), we recorded the VO₂ and SF of 7 young male volunteers walking at an increasing speed from 16.7 to 131.7 m min^-1 with 5 m min^-1 increments every 1 min, and at a decreasing speed from 106.7 m min^-1 for 5 min to 16.7 m min^-1 with 5 m min^-1 decrements every 1 min on a level treadmill. SL was also computed by dividing walking speed by SF. The VO₂ during decremental-speed walking was significantly greater compared to that during incremental-speed walking at corresponding speeds. The SF and SL could be expressed as a function of speed by SF=√13.18v and SL=0.076√ v, respectively, regardless of the different modes of walking with respect to speed. To estimate the VO₂ during walking at different speeds, the results of the increments and decrements were combined by averaging them with respect to speed (VO₂ = 1.454 × 10^-4v²-6.5 × 10^-3v+ 0.663, r=0.999, n=7). In a mathematical model of the cardiorespiratory system, the average values of VO₂ at a given speed, even though there were on- and off-phase responses, could be predicted within 7.4% of the theoretical steady-state value. These results suggest that the VO₂ against walking speed can be estimated by averaging the responses between the increments and decrements of moderate speeds. This could improve exercise tests for VO₂ estimates in terms of time and money. In addition, by using the close relationship between SF and v, VO₂ can be also expressed as a function of SF.