Change in heart rate at double product break point and validity of utilizing age-predicted heart rate at 50%VO2max due to improvement of cardiovascular fitness

Previously, we have reported that age-predicted heart rate at 50%VO2max (HR@50%VO2max) is an effective index of adjusting appropriate exercise intensity for health promotion exercise. Thus, the aim of this study is to elucidate the change in HR at double product break point (HR@DPBP) and the validity of HR@50%VO2max due to improvement of cardiovascular fitness. Ninety two healthy adults (57 +/- 9 years old), who participated in the health exercise training course, were studied. Participants were instructed how to control the intensity of physical activity for DPBP during their daily life. DPBP was determined with the use of incremental exercise test, and METs at DPBP (METs@DPBP), HR@DPBP, ratings of perceived exertion at DPBP (RPE@DPBP) were measured before and after the course. HR@50%VO2max was calculated with the following formula; 138 - age/2 (bpm). METs@DPBP significantly increased (p<0.001) after 10 weeks of the course, whereas HR@DPBP did not change. Interestingly, however, there was a significantly positive correlation (p<0.001) between amount of change in METs@DPBP and that in HR@DPBP (ΔHR@DPBP). Multiple linear regression analysis indicated this correlation was independent from sex, age and amount of change in HR at rest (p<0.001). Before and after the course, proportion of study subjects’ %ΔHRs ((HR@50%VO2max - HR@DPBP) / HR@DPBP x 100) within -10% ~ +10% were both 48.9%, and proportion of study subjects’ RPEs@DPBP within 11~13 were 92% and 85%, respectively. In this study, it was identified that significantly positive relation between amount of change in cardiovascular fitness and that of ΔHR@DPBP. This finding was independent from potentially affecting factors. In conclusion, this longitudinal study could suggest that HR@50%VO2max and RPE were valuable indexes of determining exercise intensity for health promotion exercise.