Different methods for monitoring intensity during water-based aerobic exercises

The aim of this study was to compare different measurement techniques (indirect calorimetry, IC; heart rate monitoring, HR; an activity monitoring system, AH; rates of perceived exertion, RPE) to estimate physical activity intensity (light, moderate, vigorous) during water-based aerobic exercises (WE). Twelve healthy young women performed five common WE of 10-min duration at three frequencies in an indoor swimming pool. Data recorded from the 5th to 9th minute of exercise were averaged to obtain mean \( {\dot V}\text O_2 \) (IC), HR and AH values; RPE was recorded at the end of each WE. Oxygen uptake was also estimated from HR data using three different \( {\dot V}\text O_2 \) versus HR regression equation models. Significant correlations (p < 0.001) were found for the indirect methods that used HR, RPE and AH data regressed as a function of \( {\dot V}\text O_2 \) (IC); the highest correlations were found between the measured values of \( {\dot V}\text O_2 \) (IC) and those estimated from the three \( {\dot V}\text O_2 \) versus HR equations (R > 0.7 in all cases). An ANOVA test showed no significant differences between all predicted and measured \( {\dot V}\text O_2 \) values; however, when the Bland & Altman analysis was considered, AH data showed the larger explained variances (95% CI) and the larger standard errors. These data indicate that the most accurate way to estimate physical activity intensity during WE is based on HR measurements.