Accuracy of the Polar M52 heart rate monitor for estimating energy expenditure, substrate utilization, and maximal oxygen uptake

This study investigated the accuracy of the Polar M52 heart rate monitor for estimating energy expenditure, substrate utilization, and VO_2max. Eight subjects (4 males, 4 females) between the ages of 22 and 41 participated in this study. To be eligible, participants completed a health history form and an informed consent form. Each participant completed four exercise tests (including one maximal) on separate days. VO_2max was measured by indirect calorimetry during a Bruce protocol treadmill exercise test, and was estimated using the Polar monitor. Submaximal exercise tests consisted of three 8-minutes stages on a treadmill (3, 4.5, and 5 mph), cycle ergometer (50, 100, and 150 W),and a rowing ergometer (50, 100, and 150 W). Energy expenditure and substrate utilization were measured via indirect calorimetry and estimated by the Polar monitor. Repeated measures ANOVA demonstrated that there was no difference between methods and no stage/method interaction when comparing measures of energy expenditure except on the treadmill. For the treadmill submaximal test, no overall significant differences were found in methods, but there was a significant stage/method interaction. A post-hoc paired t-test (using Bonferoni adjusted alpha) indicated that there was a significant difference (p=0.005) between methods during stage 1, but not during stages 2 and 3. The ANOVA analysis of substrate utilization showed significant differences between methods for each exercise mode. There was significant stage/method interaction on the treadmill, but not the rower or cycle. The monitor consistently overestimated the percentage of total calories derived from fat. A paired t-test indicated that there was a significant difference (p=0.015) between predicted (45.9 ml·kg·min^-1, SD 4.8) and measured (49.7 ml·kg·min^-1, SD 5.1) values of VO_2max. A significant correlation (r=0.112) was found between these measures. The conclusions of this study are that the Polar M52 heart rate monitor is accurate when estimating energy expenditure, particularly at higher exercise intensities. However, the monitor is not accurate for determining substrate utilization. Even though the monitor's estimates of VO_2max were significantly different from measured values, the predictions were reasonably accurate, underestimating actual values by an average of 38 ml·kg^-1·min^-1. Due to this accuracy, this method may be preferred to those provided by many non-exercise fitness equations or submaximal exercise testing.