Whole-Body Sweat Rate Prediction: Indoor Treadmill and Cycle Ergometer Exercise

This paper describes the development and validation of accurate whole-body sweat rate prediction equations for individuals performing indoor cycle ergometer and treadmill exercise, where power output can be measured or derived from simple inputs. For cycle ergometry, 112 trials (67 participants) were used for model development and another 56 trials (42 participants) for model validation. For treadmill exercise, 171 trials (67 participants) were used for model development and another 95 trials (63 participants) for model validation. Trials were conducted over a range of dry-bulb temperature (20˚C to 40˚C), relative humidity (14% to 60%) and exercise intensity (~40% to 85% of peak aerobic power) conditions, which were matched between model development and model validation. Whole-body sweat rates were measured, and proprietary prediction models were developed (accounting for all relevant biophysical factors) and then validated. For model validation, mean absolute error for predicted sweating rate was 0.01 and 0.02 L·h -1 for cycle and treadmill trials, respectively. The 95% confidence intervals were modest for cycle ergometer (+0.25 and -0.22 L·h -1) and treadmill exercise (+0.33 and -0.29 L·h -1). The accounted for variance between predicted and measured values was 92% and 78% for cycle and treadmill exercise, respectively. Bland-Altman analysis indicated that zero and one predicted value exceeded the a priori acceptable level of agreement (equivalent to ±2% of total body mass in 3 h) for cycle and treadmill exercise, respectively. There were fewer trials with female subjects, but their values did not differ from those expected for males. This is the foremost study to develop and validate whole-body sweat rate prediction equations for indoor treadmill and cycle ergometer exercise of moderate-to-high intensity. These prediction equations are publicly available for use (https://sweatratecalculator.com).