Author(s): TREFF, G., NEUDORFER, M.1,2, ÖTZLINGER, L.1, KUMAR, D.2, KULNIK, S.T.2, NIEBAUER, J.1,2, SMEDDINCK, J.1, SAREBAN, M.1,2, Institution: PARACELSUS MEDICAL UNIVERSITY, Country: AUSTRIA, Abstract-ID: 2330

INTRODUCTION:
Maximum oxygen consumption (VO2max) is an accepted surrogate for cardiorespiratory fitness (CRF). A laboratory-based cardiopulmonary exercise test (CPET) represents the standard to determine VO2max. If CPET is not feasible, alternative methods may be justified. The Polar® Fitness Test (PFT) is a heart-rate based test utilizing a sports-wearable, neither requiring physical exercise nor a laboratory to estimate VO2max. This makes the PFT attractive for estimating VO2max in untrained, older people and those with health issues. However, the developer validated the PFT in healthy 20-60-year olds and there is a lack of studies on the validity of VO2maxPFT in older populations. To this end, we aimed to validate the VO2maxPFT in middle-aged to older people with and without heart rate limiting medication and to compare VO2maxPFT with another clinically established surrogate for CRF, the 6-Minute Walk Test (6MWT) and five 6MWT-based VO2max estimation equations. We also aimed to explore influencing factors on the PFT’s accuracy.
METHODS:
Thirty-two participants (11 female, age 60 ± 10.2 years, VO2max 33 ± 7.7 mL/min/kg, 11 with regular heart-rate limiting medication) conducted a PFT with photoplethysmographic measurements at the wrist. VO2maxPFT was compared with VO2maxCPET and 6MWT based estimates. We analysed the data using mean absolute percentage error (MAPE), intra-class correlation coefficients (ICC), Bland-Altman plots, Pearson correlation and paired t-tests.
RESULTS:
MAPE of VO2maxCPET vs. VO2maxPFT was 17%, ICC was moderate with 0.654 (95% CI [0.402, 0.814]). The upper and lower limits of agreement in the Bland-Altman analysis were 25 mL/min/kg apart. VO2maxPFT and VO2maxCPET were strongly correlated (r = 0.670, p < 0.001) without significant difference (p=0.074).
VO2maxCPET and the distance covered in the 6MWT were strongly correlated (r = 0.676, p < 0.001). Moreover, two of the five equations estimating VO2max based on the 6MWT (Burr et al. (2011) and Porcari et al. (2021)) indicated stronger correlation with VO2maxCPET (r = 0.804 and 0.743, respectively) than VO2maxPFT did.
Exploratory analysis revealed no influence of any of the captured anthropometric, physiological or medication variables on the difference of VO2maxCPET-PFT.
CONCLUSION:
The MAPE of VO2maxPFT is 1.7-fold higher than the cut-off of 10% used in similar validation studies. Further, the limits of agreement of the VO2maxPFT are too wide to allow for an individually valid classification into the clinical fitness category proposed by e.g. the American College of Sports Medicine (2013). Hence, the PFT has insufficient validity to substitute CPET-assessments and specific 6MWT derived estimates in the population studied. PFT may be a viable alternative if patients are impaired in their ability to perform a 6MWT.

References
ACSMs Health-Related Physical Fitness Assessment Manual. Lippincott Williams & Wilkins; 2013.
Burr et al. 2011 doi:10.3810/psm.2011.05.1904
Porcari et al. 2021: doi:10.3390/jfmk6