LAUSR

Introduction/Background Exercise intensity is essential for exercise prescription. The estimation by heart rate can indicate intensity, however, this measurement can have limited accuracy, especially for low intensity exercise. One reason for inaccuracy is that exercise intensity calculations are based on heart rate at awake rest, which can easily fluctuate. In this study, we examined the validity of exercise intensity estimates generated from heart rate monitoring during sleep, which could be more stable than conscious waking heart rates. Material and method Fourteen healthy subjects participated to this study. VO2 max was determined by a maximal treadmill test to volitional exhaustion using the Bruce protocol. Maximum heart rate was estimated using age. To estimate exercise intensity during low intensity exercise, subjects participated in a six-minute distance walk (6MD). Exercise intensity was calculated using percent VO2 reserve (%VO2R), percent VO2max (%VO2max), and percent heart rate reserve based on heart rate during awake rest (HRR-a) and sleep (%HRR-s). To monitor heart rate at rest and during sleep, we employed a “smart clothing” system (Hitoe® system). Results Both %HRR-a and %HRR-s were significantly correlated with %VO2R and %VO2max. The correlation coefficient with %HRR-s tended to be higher than that of %HRR-a. The Bland-Altman plot showed systematic error in both %HRR-a and %HRR-s, with less error in %HRR-s. Conclusion Estimation of exercise intensity using heart rate during sleep may be easier and more accurate to monitor than waking heart rate, making it more feasible in clinical settings.