(72) WEARABLE HEART RATE MONITORS INTRODUCE TIME RELATED ERRORS WHEN PREDICTING VO2MAX FROM STEP TESTS

Purpose: Sub-maximal tests used to predict aerobic fitness – or VO₂max – often include heart rate and/or heart rate recovery (HRR) metrics. In particular, HRR is related to parasympathetic reactivation after physical exertion. However, many of the formulas used to predict VO₂max call for the manual palpation of heart rate. Heart rate monitoring through wearable technology is ubiquitous in current sports science and fitness applications, making the use of manual palpation antiquated. Therefore, the purpose of this study was to use heart rate monitor reported values during the recovery period to estimate VO₂ following a three-minute step test at 10 s, 15 s, and 20 s. Methods: A total of 10 participants (6 men, 4 women) were outfitted with a chest-strap worn heart rate monitor and completed the Queens College Step Test (McArdle Step Test) during which males stepped at a rate of 24 steps/min and females at 22 steps/min. Traditional instructions for this protocol ask the participants to locate their pulse in the first 5 s after exercise and then count heart beats for 15 s more. For this study, post-exercise heart rate was recorded at 10 s, 15 s, and 20 s after the completion of the test only from a wearable heart rate monitor. For men, VO₂max was calculated with the following formula: VO₂max = 111.33 – (0.42 ▪ HR) and for women, VO₂max = 65.81 – (0.1847 ▪ HR) – at each time point. A repeated-measures ANOVA, with Greenhouse Geisser adjustments, and LSD post-hoc was used to investigate pairwise comparisons at each time point (p < .05). Results: The omnibus ANOVA indicted there was a difference between time points [F(1.127,10.146) = 16.027, p = 0.002]. LSD post-hoc analysis revealed a difference between VO₂max at all time points (all pairwise p ≤ .01) 10 s (HR = 155 ± 22 bpm; VO₂max = 41.0 ± 5.6 mL·kg·min^-1), 15 s (HR = 150 ± 22 bpm; VO₂max = 42.5 ± 6.5 mL·kg·min^-1), and 20 s (HR = 146 ± 24 bpm; VO₂max = 44.0 ± 7.2 mL·kg·min^-1). Conclusions: VO₂max predictions increased by ≈ 5% after each five-second interval reported in this study. Additional research is needed to update submaximal aerobic prediction equations to use modern-day heart rate monitors, which provide more immediate feedback than manual palpation, resulting in a potential underestimation of VO₂max. Practical Applications: Practitioners should be cautious when performing common submaximal aerobic fitness assessments that were validated using manual, palpated heart rate if the athlete/client is using a wearable heart rate monitor. Mean differences and error can be introduced (≈ 10% over 10 s window) when using wearables in the place of previously-validated manual palpations – which would impact prescribed training loads or misclassification of an individual’s aerobic fitness. Acknowledgements: None.