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Kevin E. Miller, Timothy R. Kempf, Brian C. Rider, and Scott A. Conger

Background: Previous research studies have found that heart rate monitors that predict maximal oxygen consumption ( V ˙ O 2 max ) are valid for males but overestimate V ˙ O 2 max in females. Inaccurate self-reported physical activity (PA) levels may affect the validity of the prediction algorithm used to predict V ˙ O 2 max . Purpose: To investigate the validity of the Polar M430 in predicting V ˙ O 2 max among females with varying PA levels. Methods: Polar M430 was used to predict V ˙ O 2 max ( p V ˙ O 2 max ) for 43 healthy female study participants (26.9 ± 1.3 years), under three conditions: the participant’s self-selected PA category (sPA), one PA category below the sPA (sPA − 1), and one category above the sPA (sPA + 1). Indirect calorimetry was utilized to measure V ˙ O 2 max ( m V ˙ O 2 max ) via a modified Astrand treadmill protocol. Repeated-measures analyses of covariance using age and percentage of body fat as covariates were used to detect differences between groups. Bland–Altman plots were used to assess the precision of the measurement. Results: p V ˙ O 2 max was significantly correlated with m V ˙ O 2 max (r = .695, p < .001). The mean values for p V ˙ O 2 max and m V ˙ O 2 max were 44.58 ± 9.29 and 43.98 ± 8.76, respectively. No significant differences were found between m V ˙ O 2 max , p V ˙ O 2 max , sPA – 1, and sPA + 1 (p = .492). However, the Bland–Altman plots indicated a low level of precision with the estimate. Conclusions: The Polar M430 was a valid method to predict V ˙ O 2 max across different sPA levels in females. Moreover, an under/overestimation in sPA had little effect on the predicted V ˙ O 2 max .

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Alexander H.K. Montoye, Olivia Coolman, Amberly Keyes, Megan Ready, Jaedyn Shelton, Ethan Willett, and Brian C. Rider

Background: Given the popularity of thigh-worn accelerometers, it is important to understand their reliability and validity. Purpose: Our study evaluated laboratory validity and free-living intermonitor reliability of the Fibion monitor and free-living intermonitor reliability of the activPAL monitor. Free-living comparability of the Fibion and activPAL monitors was also assessed. Methods: Nineteen adult participants wore Fibion monitors on both thighs while performing 11 activities in a laboratory setting. Then, participants wore Fibion and activPAL monitors on both thighs for 3 days during waking hours. Accuracy of the Fibion monitor was determined for recognizing lying/sitting, standing, slow walking, fast walking, jogging, and cycling. For the 3-day free-living wear, outputs from the Fibion monitors were compared, with similar analyses conducted for the activPAL monitors. Finally, free-living comparability of the Fibion and activPAL monitors was determined for nonwear, sitting, standing, stepping, and cycling. Results: The Fibion monitor had an overall accuracy of 85%–89%, with high accuracy (94%–100%) for detecting prone and supine lying, sitting, and standing but some misclassification among ambulatory activities and for left-/right-side lying with standing. Intermonitor reliability was similar for the Fibion and activPAL monitors, with best reliability for sitting but poorer reliability for activities performed least often (e.g., cycling). The Fibion and activPAL monitors were not equivalent for most tested metrics. Conclusion: The Fibion monitor appears suitable for assessment of sedentary and nonsedentary waking postures, and the Fibion and activPAL monitors have comparable intermonitor reliability. However, studies using thigh-worn monitors should use the same monitor brand worn on the same leg to optimize reliability.