Author(s): BUCKLEY, J., JONES, S., BUCKLEY, J.P., Institution: KEELE UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 1470

INTRODUCTION:
Recent developments in wearable foot-pod technology have provided an equivalent measure of power for runners, similar to what cyclists have enjoyed for many years. A direct measure of power (Watts) during running, as with cycling, thus has the utility for developing a correlation from which to estimate a rate of oxygen uptake (VO2) for a given Watt. The aim of this study was to test the possibility of estimating VO2 from power output during free outdoor running at a self-selected pace, and then deriving a formula to account for changes in this relationship affected by the ground-surface gradient.
METHODS:
Fifteen healthy active participants (12 male: 26 ± 6 yrs; 3 female 28 ± 3 yrs) completed three mins of running on each of three different gradients: flat athletics track, 5° uphill and 5° downhill paved foot path. Power output was measured continuously via a shoe-lace attached foot-pod (Stryd Power Monitor, Boulder, Colorado) and similarly for VO2 via a portable wearable pulmonary gas exchange monitor (Cortex MetaMax 3B, Leipzig).
RESULTS:
The key results are summarised with four key measures as group means ± SD and analysis of variance statistic (ANOVA):
1. Running power (Watts/kg): Flat = 3.4 ± 0.5; Uphill = 3.9 ± 0.7 (+14.7%∆ vs flat); Downhill = 3.1 ± 0.5 (-8.8%∆ vs flat); ANOVA F=27.9, DF=2 p<0.001

2. Stryd Device equation Estimated VO2 (ml•kg-1•min-1) = 13.16 x Watts/kg: Flat = 46.0 ± 7.4; Uphill = 53.4 ± 9.6 (+16.1 %∆ vs flat); Downhill = 42.3 ± 6.9 (-8.0 %∆ vs flat); ANOVA F=27.7, DF=2 p<0.001

3. Actual VO2 (ml•kg-1•min-1): Flat = 38.7 ± 7.8; Uphill = 40.5 ± 5.6 (+4.7 %∆ vs flat); Downhill = 37.2 ± 6.7 (-3.9 %∆ vs flat); ANOVA F=5.58, DF=2 p=0.015

4. VO2 to Watts Ratio: Flat = 10.0; Uphill = 13.3 (+33 %∆ vs flat); Downhill = 4.3 (-57 %∆ vs flat); ANOVA F = 196.4, DF = 1 p<0.001
Power output and VO2 changed significantly (P<.001) across the three gradients. Compared to flat surface running, the proportional %changes of the respective foot-pod estimated VO2 for running uphill and downhill (+14.7%, -8.8%) remained similar to the respective %change in power output (+16.1, -8.8%). Whereas, the %change in actual VO2 for uphill and downhill running, respectively, were significantly smaller (+4.7%, -3.9%; p<.001). For all three conditions the foot-pod equation for estimating VO2 were significantly lower than actual VO2 (p <.001), and such differences were magnified when expressed as ratio of VO2 to Power.
CONCLUSION:
Whilst the Stryd Power foot-pod monitor is able to show reliable and valid changes in running power with changes in both running speed and surface gradient [1], there still remains the need to develop a much more accurate formula for estimating VO2 from power output that accounts for both running speed and surface gradient.
1. Cerezuela, V., et al. Eur J Sport Sci. 2021; 21(3):341-350