Relative heart rate, heart rate reserve, and VO2 during submaximal exercise in the elderly

Background. The purpose of this study was to examine the relationships among relative maximal heart rate (%HRmax), maximal heart rate reserve (%HRmax reserve), and maximal oxygen uptake (%V[O.sub.2]max) during submaximal exercise by elderly subjects. Methods. V[O.sub.2]max and HRmax were determined on 36 women and 19 men, 60 to 80 yrs of age, by a maximal treadmill test to volitional exhaustion. On a separate day, subjects underwent a submaximal treadmill protocol consisting of three 6-min exercise stages at treadmill speeds and grades estimated to elicit 40%, 60%, and 80% of HRmax reserve. Cardiorespiratory responses were determined during mins 4-5 and 5-6 of each stage. Results. Measured exercise intensities expressed by the three methods were: %HRmax reserve = 36, 55, and 79%; %HRmax = 65, 75, and 88%; % V[O.sub.2]max = 53, 69, and 88%. %HRmax was greater (p < .05) than % V[O.sub.2]max at 53 and 69% of V[O.sub.2]max. %HRmax reserve was less (p < .05) than % V[O.sub.2]max for all three intensities. Slopes and intercepts for the linear regression equations relating % V[O.sub.2]max with %HRmax and with %HRmax reserve differed between men and women (p < .05). The regression equation relating % V[O.sub.2]max and %HRmax was y = -22.8 + 1.2 (%HRmax) -13.0 (Gender) + 0.2 (%HRmax x Gender): standard error of the estimate (SEE) = 9.7% and [R.sup.2] = .71. The regression equation relating % V[O.sub.2]max and %HRmax reserve was y = 32.4 + 0.7 (%HRmax reserve) -10.9 (Gender) + 0.2 (%HRmax reserve x Gender): SEE = 9.8% and [R.sup.2] = .70 (Gender: F = 0; M = 1). Conclusions. The data indicate that there is considerable variability among methods of expressing exercise intensity and that %HRmax more closely represents % V[O.sub.2]max than does %HRmax reserve (p < .05) in older adults. These results are in contrast to what has been shown with younger subjects and with American College of Sports Medicine guidelines for exercise prescription.