The heart rate method for estimating oxygen uptake: analyses of reproducibility using a range of heart rates from commuter walking.

BACKGROUND: The heart rate method, based on the linear relation between heart rate and oxygen uptake, is potentially valuable to monitor intensity levels of physical activities. However, this depends not least on its reproducibility under standard conditions. This study aims, therefore, to evaluate the reproducibility of the heart rate method in the laboratory using a range of heart rates associated with walking commuting. METHODS: On two different days, heart rate and oxygen uptake measurements were made during three submaximal (model 1) and a maximal exercise intensity (model 2) on a cycle ergometer in the laboratory. 14 habitual walking commuters participated. The reproducibility, based on the regression equations from test and retest and using three levels of heart rate from the walking commuting, was analyzed. Differences between the two models were also analyzed. RESULTS: For both models, there were no significant differences between test and retest in the constituents of the regression equations (y intercept, slope and r value). Neither were there any systematic differences in estimated absolute levels of VO2 between test and retest for either model. However, some rather large individual differences were seen in both models. Furthermore, no significant differences were seen between the two models in slopes, intercepts and r values of the regression equations or in the estimated VO2. CONCLUSION: The heart rate method shows good reproducibility on the group level in estimating oxygen consumption from heart rate-oxygen uptake relations in the laboratory, and based on three levels of heart rate which are representative for walking commuting.

Heart Rate Methods Can Be Valid for Estimating Intensity Spectrums of Oxygen Uptake in Field Exercise.

PURPOSE: Quantifying intensities of physical activities through measuring oxygen uptake (V̇O2) is of importance for understanding the relation between human movement, health and performance. This can in principle be estimated by the heart rate (HR) method, based on the linear relationship between HR and V̇O2 established in the laboratory. It needs, however, to be explored whether HR methods, based on HR-V̇O2 relationships determined in the laboratory, are valid for estimating spectrums of V̇O2 in field exercise. We hereby initiate such studies, and use cycle commuting as the form of exercise. METHODS: Ten male and ten female commuter cyclists underwent measurements of HR and V̇O2 while performing ergometer cycling in a laboratory and a normal cycle commute in the metropolitan area of Stockholm County, Sweden. Two models of individual HR-V̇O2 relationships were established in the laboratory through linear regression equations. Model 1 included three submaximal work rates, whereas model 2 also involved a maximal work rate. The HR-V̇O2 regression equations of the two models were then used to estimate V̇O2 at six positions of field HR: five means of quintiles and the mean of the whole commute. The estimations obtained were for both models compared with the measured V̇O2. RESULTS: The measured quintile range during commuting cycling was about 45-80% of V̇O2max. Overall, there was a high resemblance between the estimated and measured V̇O2, without any significant absolute differences in either males or females (range of all differences: -0.03-0.20 L⋅min-1). Simultaneously, rather large individual differences were noted. CONCLUSION: The present HR methods are valid at group level for estimating V̇O2 of cycle commuting characterized by relatively wide spectrums of exercise intensities. To further the understanding of the external validity of the HR method, there is a need for studying other forms of field exercises.

The effects of group and single housing and automated animal monitoring on urinary corticosterone levels in male C57BL/6 mice.

Mice are used extensively in physiological research. Automated home-cage systems have been developed to study single-housed animals. Increased stress by different housing conditions might affect greatly the results when investigating metabolic responses. Urinary corticosteroid concentration is considered as a stress marker. The aim of the study was to compare the effects of different housing conditions and an automated home-cage system with indirect calorimetry located in an environmental chamber on corticosterone levels in mice. Male mice were housed in different conditions and in automated home-cage system to evaluate the effects of housing and measuring conditions on urine corticosterone levels. Corticosterone levels in single-housed mice in the laboratory animal center were consistently lower compared with the group-housed mice. Single-housed mice in a separate, small animal unit showed a rise in their corticosterone levels a day after they were separated to their individual cages, which decreased during the following 2 days. The corticosterone levels of group-housed mice in the same unit were increased during the first 7 days and then decreased. On day 7, the corticosterone concentrations of group-housed mice were significantly higher compared with that of single-housed mice, including the metabolic measurement protocol. In conclusion, single housing caused less stress when compared with group-housed mice. In addition, the urine corticosterone levels were decreased in single-housed mice before the metabolic measurement started. Thus, stress does not affect the results when utilizing the automated system for measuring metabolic parameters like food and water intake and calorimetry.