Estimation of Cardiopulmonary Fitness during Daily Activity

Abstract

Cardiopulmonary fitness (CPF), the ability to provide inhalational oxygen to the exercising muscle, is one component of health-related physical fitness — one of the main goals of exercise, and is related to all-cause and cardiovascular mortality. Increased fitness is associated with lower mortality. The maximum uptake of oxygen (VO2max) is the representative index of CPF. Studies indicating a decrease in all-cause mortality with the improvement of CPF emphasize the importance of CPF in health care. Nevertheless, CPF has not received due attention, at least in part because of the lack of practical and reliable methods to measure it. Despite metabolic gas analysis during maximal exercise being the gold standard measurement of VO2max, it is not safe for high-risk groups because of the requirement for high intensity exercise, and high levels of motivation are required to complete the test. The submaximal exercise test also requires specific equipment, and can be affected by familiarity with the test protocol. Numerous non-exercise estimation methods which use anthropometric parameters and individual self-reported physical activity, or pedometers. Non-exercise estimations do not measure biological responses to physical activity. Moreover, self-reported physical activity could be inaccurate. Recently, CPF has been estimated by continuous HR and accelerometric physical activity monitoring with or without a specific exercise protocol. Fitter individuals with a higher level of VO2max are assumed to be more active with a lower HR than unfit individuals with a lower level of VO2max. Although these methods are simple and safe for high-risk groups, they also involve a specific exercise protocol that cannot be applied to daily life. VO2max estimation without exercise however, requires prolonged measurement at least seven days with attached sensors, making these methods impractical. The VO2max of 23 healthy, sedentary men was measured by using the maximal exercise test. Corresponding heart rate and activity energy expenditure data were also recorded. The maximum activity energy expenditure was estimated by age, using the first 12 hours of activity energy expenditure, and heart rate data recorded from 4 days of typical daily life. Participants were divided into training (n = 15) and test (n = 8) groups, according to activity energy expenditure, and a regression model for estimating VO2max was developed. The activity energy expenditure estimated from 12 hours of daily living correlated significantly with the measured VO2max value, and recording beyond 12 hours did not improve the estimation. In addition, the estimated maximum oxygen uptake agreed with the measured maximum oxygen uptake value. The accuracy of the model compared well with previous maximum oxygen uptake estimation studies.