Purpose: This study focused on developing a new method to assess V̇O2max outside laboratory conditions and without the need for maximal exertion. We hypothesized that the combined use of accelerometry and HR monitoring, under daily life conditions, could provide a good estimate of physical fitness.
Methods: Twenty-six healthy subjects (15 women, 11 men), aged 28 ± 7 yr, performed a maximal incremental test on a bicycle ergometer to determine V̇O2max. Body composition was measured with underwater weighing and deuterium dilution using a three-compartment model. A triaxial accelerometer (Tracmor) and an HR monitor were worn for seven consecutive days under free-living conditions. The ratio of HR to activity counts per minute (ACM) was used as a fitness index (HR·ACM−1).
Results: As hypothesized, HR·ACM−1 was significantly correlated with V̇O2max. Using fat-free mass (FFM) (P < 0.0001), age (P = 0.025), and HR·ACM−1 (P = 0.021) as the independent variables, the explained variation in V̇O2max was 76% (P < 0.0001, SEE = 363 mL·min−1). In order to generate a prediction formula that is applicable in the field when no data on body composition are available, the same analysis was done with body mass and gender in the model instead of FFM. HR·ACM−1 was significantly (P = 0.023) correlated with V̇O2max. The total explained variation of the model was 71%, with a SEE of 409 mL·min−1, or 13.7% of the average V̇O2max.
Conclusion: After correction for body composition, V̇O2max was significantly related to HR·ACM−1. It is, to our knowledge, the first tool that yields a measure of V̇O2max by monitoring people in their daily life activities without the need for a specific protocol or for maximal exertion, and therefore is applicable to a large variety of subjects.