Relative Heart Rate, Heart Rate Reserve, and Vo 2 During Submaximal Exercise in the Elderly

Journal of Gerontology: MEDICAL SCIENCES 1996. Vol. 5IA. No. 4, MI65-MI71 Copyright 1996 by The Gerontological Society of America Relative Heart Rate, Heart Rate Reserve, and Vo 2 During Submaximal Exercise in the Elderly Lynn B. Panton, 1-3 James E. Graves, 12-3 Michael L. Pollock, 12-3 Linda Garzarella, 1-3 Joan F. Carroll, 1-3 Scott H. Leggett, 1-3 David T. Lowenthal, 4 and Greg J. Guillen 4 'Center for Exercise Science and Departments of 2 Medicine and 3 Exercise and Sport Sciences, University of Florida. 4 VA Medical Center, Gainesville, Florida. Background. The purpose of this study was to examine the relationships among relative maximal heart rate (), maximal heart rate reserve ( reserve), and maximal oxygen uptake (%Vo 2 max) during submaximal exercise by elderly subjects. Methods. Vo 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: reserve = 36, 55, and 79%; = 65, 75, and 88%; % Vo 2 max = 53, 69, and 88%. was greater (p <.05) than % Vo 2 max at 53 and 69% of Vojmax. reserve was less (p <.05) than % Vo 2 max for all three intensities. Slopes and intercepts for the linear regression equations relating % Vo 2 max with and with reserve differed between men and women (p <.05). The regression equation relating % Vo 2 max and was y = -22.8 + 1.2 () -13.0 (Gender) + 0.2 (X Gender): standard error of the estimate (SEE) = 9.7% and R 2 =.71. The regression equation relating % Vo 2 max and reserve was y = 32.4 + 0.7 ( reserve) -10.9 (Gender) + 0.2 ( reserve x Gender): SEE = 9.8% and R 2 =.70 (Gender: F = 0; M = 1). Conclusions. The data indicate that there is considerable variability among methods of expressing exercise intensity and that more closely represents % Vo 2 max than does 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. INTENSITY of exercise is a primary component of exercise prescription and refers to the relative amount of energy required to perform a specific aerobic activity (1,2,3)- Studies suggest that exercise intensity is the most important factor for the development and maintenance of cardiorespiratory fitness (2,4). To determine and maintain a desired training intensity, oxygen uptake (Vo 2 ) or some equivalent index must be measured. Since heart rate (HR) is easy to measure and is linearly related to Vo 2, it is often used to monitor aerobic training intensity (3,5,6,7). There are three common methods for establishing training intensity based upon HR. The most direct method requires the measurement of steady-state HR and Vo 2 at two or more submaximal exercise intensities and the subsequent calculation of a regression equation relating these two variables (8). This method, although accurate, is time-consuming and requires elaborate laboratory equipment. Another way to calculate training intensity based upon HR is the percent of maximal HR () method. This method computes the training HR as a percentage of HRmax. Although this method requires only the measurement of HRmax, it is limited by the individual variability in the relationship between relative HRmax and relative Vo 2 max (3,9). This variability is due partially to differences among individuals in resting HR (8). The third method of establishing training intensity from HR uses the subject's potential HR increase (HR reserve) and assumes that resting HR represents zero intensity (5). This corrects for the nonzero value of resting HR. A percentage of the difference between maximal HR and resting HR is calculated and the resulting value is then added to the resting HR. This method is referred to as the Karvonen or reserve method and requires valid measurements of both resting and maximal HRs. Numerically, the method exceeds %Vo 2 max whereas reserve relates closely with %Vo 2 max through a wide range of exercise intensities in young and middle-aged subjects (1,2,7,8,10). Based on studies with cardiac patients, Hellerstein (11) stated that the close relationship between reserve and %Vo 2 max is independent of age, fitness, or extent of coronary artery disease. However, the relationship between HR and Vo 2 has not been systematically studied in the elderly. Several studies suggest that reserve underestimates % Vo 2 max during submaximal exercise in the elderly (12,13,14). This has significant implications for the prescription of exercise in older adults since %Vo 2 max achieved using reserve to establish intensity may exceed safe or desirable limits. The purpose of the present study was to further examine the relationship between, reserve, and M165

M166 PANTONETAL. %Vo 2 max in an elderly population of men and women through a range of submaximal exercise intensities. METHODS Subjects. Eighty-three men and women, 60 to 80 yr of age, were recruited from the Gainesville community to participate in the study. After screening (see below), 19 men and 36 women were selected. Subject characteristics are presented in Table 1. Many subjects were physically active but none participated in a regular exercise training program. The study was approved by the University of Florida College of Medicine Institutional Review Board. Documented informed consent was obtained from all subjects. Screening. During their first visit to the laboratory, subjects completed medical history, demographic, physical activity, smoking, and nutrition questionnaires. Subjects were then administered a cardiovascular and physical examination that included a resting 12 lead electrocardiogram (ECG). If any clinically significant findings such as hypertension (blood pressure (BP) exceeding 160/100 mmhg at rest), angina pectoris, or an abnormal resting ECG (ST segment depression or elevation that is horizontal or downsloping greater than 1 mm,.08 sec from the J-point, or the presence of abnormal Q waves) were found, the subjects were excluded from the study. Subjects who passed the initial screening were then administered a physician-supervised diagnostic graded exercise test (GXT) using a modified (2 min stages) Naughton protocol (15). The GXT was terminated when the subjects were unable to continue or when signs or symptoms of cardiovascular decompensation became evident (1). Based on the physical examination, resting ECG, and the GXT, 21 subjects were disqualified from participating in the study. Seven subjects who were taking Beta-blockers were also excluded from the study. The subjects included in this study were free of overt evidence of hypertension, coronary artery disease, did not take medications that might alter the relationship between heart rate and Vo 2, and had no orthopedic or other medical conditions that would contra-indicate exercise testing or training. Measurement of maximal aerobic capacity. Subjects included in the study returned to the laboratory on a subsequent day to undergo another treadmill GXT (modified Naughton protocol) to measure maximal Vo 2, HR, ventilation (VE), respiratory exchange ratio (RER), systolic (SBP) and diastolic (DBP) blood pressures, and rating of perceived exertion (RPE) (16). For those subjects who exercised Table 1. Physical Characteristics of the Subjects, Means ± SD Variable Age (yr) Weight (kg) Height (cm) Men (n = 19) 68.7 ± 5.1 78.8 ± 8.9 174.7 ± 6.0 Women (n = 36) 68.6 ± 5.7 63.8 ± 12.8* 159.9 ± 5.8* *Women are significantly different from men, p <.05. Combined (N = 55) 68.6 ± 5.4 69.0 ± 13.6 165.0 ± 9.2 longer than 12 min on their previous GXT, the initial speed was set at 3 mph rather than 2 mph. The test was terminated when the subject was unable to continue. During this test, expired air was routed through a Medical Graphics (St. Paul, MN) metabolic cart (model CPX) for measurement of oxygen and carbon dioxide gas concentrations and ventilatory volumes. Expired air was also collected minute by minute in meteorological balloons. The concentrations of oxygen and carbon dioxide in the meteorological balloons were determined using Ametek-Thermox (Pittsburgh, PA) gas analyzers, and ventilatory volumes were measured using a 120 liter Tissot spirometer (W.B. Collins, Braintree, MA). The metabolic cart and component gas analyzers were calibrated with primary standard gas mixtures. All subjects met at least two of the following criteria for the determination of Vo 2 max: (a) HRmax at or above age predicted HRmax (220- age); (b) an RER greater than or equal to 1.1; and (c) a leveling off of Vo 2 during the last minute of the test (change in Vo 2 =s 200 ml). Heart rates were determined from 12-lead ECG recordings (Quinton Instruments, Seattle, WA) taken over the last 10 seconds of each minute during the test and at maximal exercise. Blood pressure measurements were taken every 2 min at the end of each stage using the inflatable cuff method. Ratings of perceived exertion were taken every minute of the exercise test and at maximal exertion. Measurement of resting HR and calculation of percentage of HRmax reserve. Standing resting HR was measured prior to the initial GXT and the Vo 2 max GXT, and after a 15- min seated rest period prior to the submaximal treadmill test. The resting HR used to calculate reserve was the lowest of the three standing HR measurements. HRmax was measured during the initial GXT and the Vo 2 max test. The highest HRmax was used to calculate the HRmax reserve (HRmax-resting HR). Submaximal treadmill exercise test. Prior to administration of the submaximal treadmill test, subjects began an exercise training program for approximately 2 weeks. During the 2-week period, training was conducted 3 times per week for 20 to 30 min at an average intensity of 57 ± 8% of HRmax reserve. All subjects exercised on a treadmill during the first week of training. Beginning with the second week of training, exercise was either uphill walking on a treadmill or stair climbing (Stairmaster, Seattle, WA). The training completed prior to the submaximal test served two purposes. The first purpose was to familiarize the subjects with submaximal exercise lasting at least 20 min. The second purpose was to estimate treadmill speed and percent grade combinations (workloads) that would elicit 40%, 60%, and 80% of the HRmax reserve for each subject. This was done by manipulating treadmill speed and grade and observing the subjects' HR responses during a training session. The submaximal exercise test protocol consisted of three consecutive 6-min exercise stages. Walking speed was held constant at a comfortable rate for each subject during the three stages; grade was set to the predetermined grade that elicited the desired HR. This was an incremental protocol in that all subjects completed the 40% stage first (stage 1), followed by the 60% stage (stage 2), and finally the 80%

HEART RATE, HEART RATE RESERVE, AND Vo 2 M167 stage (stage 3). Resting SBP, DBP, and HR were taken following 15 min of seated rest and following 2 min of quiet standing. Heart rate was continuously recorded using leads II, av F, and V5 during the standing rest and 18 min of submaximal exercise. Expired air was collected during min 4-5 and 5-6 of each 6-min stage. Procedures for collecting and determining submaximal Vo 2, VE, and RER were identical to those used for the Vo 2 max test. Blood pressure and RPE were also measured during minutes 4-5 and 5-6 of each 6-min stage. Data analyses. Means and standard deviations were calculated for age, height, weight, and the physiological parameters measured during maximal and submaximal exercise. Descriptive characteristics of the men and women were compared using an independent Z-test. To verify steadystate exercise conditions during the submaximal treadmill test, a one-way ANOVA for repeated measures over time (2 levels) was used to determine if there were differences in the measured physiological parameters during min 4-5 and 5-6 of each 6-min exercise stage. Paired Z-tests were used to determine if there were differences between and %Vo 2 max and between reserve and %Vo 2 max at the three exercise intensities. Multiple regression analysis was used to determine the model of best fit for the relationship between %Vo 2 max and reserve and between %Vo 2 max and. The coefficient of determination (R 2 ) and standard error of the estimate (SEE) were calculated for all regression equations. For all analyses, statistical significance was accepted at/? <.05. Statistical procedures were done using the SAS means, general linear models, and regression procedures (17). RESULTS Resting HR and physiological parameters obtained at maximal exercise are presented in Table 2. There was no difference in maximal HR, RER, RPE, SBP or DBP between the men and women. However, the men had a lower resting HR and ventilatory equivalent, and a higher relative Vo 2 max, absolute Vo 2 max, VEmax, and maximal oxygen pulse than the women. Physiological parameters measured during min 4-5 and 5-6 of the three submaximal exercise stages are presented in Table 3. Although there were statistical differences for some of the variables, the magnitude of observed differences was small and not considered significantly important. Oxygen uptakes during min 4-5 and 5-6 were not statistically different. Thus, subjects were considered to be at steady state during the last 2 minutes of each of the three 6-min stages. The steady-state values were averaged to obtain criterion measures for analysis. %Vo 2 max,, and reserve at the three submaximal exercise stages are compared in Table 4. Measured Vo 2 s (mean of min 4-5 and 5-6) for the submaximal exercise stages represented 53 ± 9% (stage 1), 69 ± 10% (stage 2), and 88 ± 12% (stage 3) of Vo 2 max. There were significant differences between %Vo 2 max and Variable Table 2. Resting Heart Rate and Physiological Parameters Obtained During Maximal Exercise, Means ± SD Resting HR HRmax Vo 2 max relative Vo 2 max absolute VEmax RERmax RPEmax SBPmax DBPmax Max Oxygen Pulse Max VE/VO 2 Men (n--= 19) 68.1 164.4 27.7 2.17 87.0 1.16 19.5 199.0 90.0 13.3 39.8 ± 7.8 ± 13.4 ± 3.7 ± 0.35 ± 22.5 ± 0.1 ± 0.5 ± 21.0 ± 12.0 ± 2.2 ± 8.7 Women (n = 36) 75.5 dt 9.9* 164.0 dt 12.1 21.9 dt 4.2* 1.38 dt 0.31* 56.5 dt 15.4* 1.14 dt 0.1 19.3 dt 1.0 189.0 dt 22.0 88.0 dt 11.0 8.4 dt 2.0* 41.3 dt 7.7* Combined (N = 55) 72.9 : t 9.8 164.1 dt 12.4 23.9 dt 4.9 1.65 dt 0.50 67.0 : t 23.2 1.15 dt 0.1 19.3 dt 0.9 193.0 dt 22.0 89.0 : t 12.0 10.1 : t 3.1 40.8 dt 8.0 Notes. HR = heart rate (b/min); HRmax = maximal heart rate (b/min); Vo 2 max relative = relative maximal oxygen uptake (ml'kg- u min"'); Vo 2 max absolute = absolute maximal oxygen uptake (L/min); VEmax = maximal ventilation (L/min); RERmax = maximal respiratory exchange ratio; RPEmax = maximal rating of perceived exertion; SBPmax = maximal systolic blood pressure (mmhg); DBPmax = maximal diastolic blood pressure (mmhg); Maximal Oxygen Pulse (ml/beat); Maximal VE/ Vo 2 = maximal ventilatory equivalent. * Women are significantly different from men (p <.05). Table 3. Physiological Data for Minutes 4 5 and 5-6 of Each Submaximal Workload (N = 55), Means ± SD Variables RPE SBP DBP RER VE HR Relative Vo 2 Absolute Vo 2 O 2 Pulse VE/VO 2 Tl Stage 1 T2 Tl Stage 2 T2 Tl Stage 3 T2 10.6 ± 1.4 152 ± 23 81 ± 10 0.81 ± 24.9 ± 0.07 6.9 105 ± 11 12.3 ± 0.85 ± 8.2 ± 29.6 ± 2.0 0.23 2.5 4.8 11.1 151 81 0.82 25.2 106 12.5 0.86 8.2 29.6 ± 1.4* ± 22 ± 10 ± 0.07* ± 6.7 ± 11* ± 2.0 ±.22 ± 2.5 ± 4.7 12.8 ± 1.4 168 ± 22 80 ± 11 0.90 ± 33.9 ± 0.07 10.4 123 ± 14 16.2 ± 1.12 ± 9.3 ± 30.6 ± 3.0 0.31 2.8 4.8 13.1 ± 1.6* 169 ± 22 80 ± 11 0.90 ± 34.7 ± 0.07 10.8* 124 ± 14* 16.4 ± 1.13 ± 9.3 ± 30.9 ± 3.0 0.32 2.9 4.9* 14.7 ± 1.9 182 ± 24 83 ± 12 0.99 ± 47.9 ± 0.09 16.3 145 ± 16 20.7 ± 1.43 ± 10.0 ± 33.6 ± 4.2 0.42 3.1 5.9 15.2 ± 2.1* 183 ± 24 82 ± 12 0.98 ± 48.6 ± 0.09 17.2 145 ± 17 20.8 ± 1.44 ± 10.0 ± 33.8 ± 4.2 0.43 3.1 6.1 Notes. RPE = rating of perceived exertion; SBP = systolic blood pressure (mmhg); DBP = diastolic blood pressure (mmhg); RER = respiratory exchange ratio; VE = ventilation (L/min); HR = heart*rate (b/min); Relative Vo 2 = Relative oxygen uptake (ml*kg- u min-'); Absolute Vo 2 = absolute oxygen uptake (L/min); O 2 Pulse = O 2 pulse (ml/beat); VE/VO 2 = Ventilatory Equivalent. *Minutes 5-6 values are significantly different from corresponding Minutes 4-5 values (p <.05).

M168 PANTONETAL. Table 4. Mean Relative HRmax Reserve, HRmax, and Vo 2 max at Each Workload, Means ± SD Variable Combined {N = 55) %Vo 2 max reserve Women (n = 36) %Vo 2 max reserve Men (/i = 19) %Vo 2 max reserve Stage 1 53.1 ± 36.1 ± 64.6 ± 54.3 ± 36.5 ± 65.8 ± 50.9 ± 35.5 ± 62.2 ± 9.3 8.1* 5.8* 10.1 8.5* 5.7* 7.2 7.4* 5.5* Stage 2 69.3 ± 10.3 55.3 ± 9.4* 75.1 ± 6.4* 69.9 ± 9.8 56.5 ± 9.3* 76.5 ± 6.0* 68.2 ± 11.5 52.9 ± 9.3* 72.3 ± 6.6* *(p <.05), significantly different from %Vo 2 max. Stage 3 87.9 ± 12.3 79.2 ± 12.3* 88.3 ± 7.3 87.3 ± 12.4 79.7 ± 12.7* 89.0 ± 7.1 89.1 ± 12.4 78.1 ± 11.8* 86.9 ± 7.7 - %V0,max - - Reserve 20 40 S3 60 69 80 88 100 %HR max, Reserve, and %V0,max Figure 1. Percent maximal heart rate (), maximal heart rate reserve ( reserve), and maximal oxygen uptake (%V"o 2 max) in men and women 60 to 80 years of age (JV = 55). *p <.05. during stage 1 and stage 2, and between %Vo 2 max and reserve during all three stages. For the overall sample, reserve was significantly less than the measured %Vo 2 max by 17.0%, 14.0%, and 8.8% at 53%, 69%, and 88% of Vo 2 max, respectively. was significantly greater than %Vo 2 max by 11.5% and 5.8% at 53% and 69% of %Vo 2 max, respectively. Separating the total sample by gender had little influence on this finding: reserve was less than %Vo 2 max for men (15.5%, 15.2%, 11.0%) and women (17.8%, 13.4%, 7.6%) at 53%, 69%, and 88% Vo 2 max, respectively. was greater than %Vo 2 max for both men (11.3% and 4.2%) and women (11.5% and 6.6%) at 53% and 69% Vo 2 max, respectively. Analysis of the mean differences between reserve and %Vo 2 max and between and %Vo 2 max indicated that the method more closely represents measured %Vo 2 max than did reserve during submaximal exercise between 53% and 88% of Vo 2 max (Figure 1). Multiple regression analysis indicated that gender significantly influenced both the intercept and the slope of the linear models developed to predict %Vo 2 max from both and reserve. Thus, gender was included as a variable in the prediction equations. The model for predicting %Vo 2 max from and gender (Figure 2) was %Vo 2 max = -22.8 + 1.2 () - 13.0 (Gender) + 0.2 ( x Gender) where Gender is 1 for men and 0 for women. The coefficient of variation (R 2 ) for this model was R 2 =.71 and the SEE = 9.7%. The model for predicting %Vo 2 max from reserve and gender (Figure 3) was %Vo 2 max = 32.4 + 0.7 ( reserve) - 10.9 (Gender) + 0.2 ( reserve x Gender) with an R 2 =.70 and an SEE = 9.8%. 120 100 80 O 60 Women Men 20 40 60 80 100 120 Figure 2. Maximal oxygen uptake (%Vo 2 max) and percent maximal heart rate () in elderly men and women (N = 55). For the combined sample y = -.22.8 + 1.2()- 13.0 (Gender) + 0.2( x Gender): SEE = 9.7% and/? 2 =.71; Gender: M = I, F = 0. DISCUSSION Percent HRmax Reserve. This study did not find a close agreement between %Vo 2 max and reserve in elderly men and women at exercise intensities between 53 and 88% of Vo 2 max. Previous research on young persons and cardiac patients has shown that reserve 20 40 Reserve Figure 3. Maximal oxygen uptake (%Vo 2 max) and percent maximal heart rate reserve ( reserve) in elderly men and women (N = 55). For the combined sample y = 32.4 + 0.7 ( reserve) - 10.9 (Gender) + 0.2 ( reserve x Gender): SEE = 9.8% and/? 2 =.70; Gender: M = 1,F = 0.

HEART RATE, HEART RATE RESERVE, AND Vo 2 M169 equates well with %Vo 2 max (within 2 to 4%) at exercise intensities between 25% and 85% of %Vo 2 max (8,11). Although only a few studies examined the relationship between %Vo 2 max and reserve, guidelines for exercise prescription to develop and maintain cardiorespiratory fitness have been established based on the reserve method (1,2,7). It has been suggested that the relationship between %Vo 2 max and reserve is independent of age, fitness level, or extent of coronary artery disease (11). This is the first study to systematically evaluate the relationship between %Vo 2 max and reserve in an elderly population, and it does not support the assumption that the close relationship between %Vo 2 max and reserve is independent of age or fitness levels. The conclusion of Hellerstein (11) that there is a close relationship between %Vo 2 max and reserve may be related to the cardiac patients being evaluated with a symptom-limited, rather than a maximal GXT. A symptomlimited GXT rarely meets the criteria for a true Vo 2 max due to restrictions in angina, ECG changes, blood pressure changes, and/or achievement of target heart rate. Thus, lower maximal heart rates are obtained leading to a greater reserve at any given submaximal heart rate. This would compensate for the low fitness levels in these cardiac patients. In an older population where fitness levels are relatively low (approximately 20 ml - mg~ l# min~ l ) and maximal heart rates are relatively high (approximately 12 beats above 220-age) there would be an overprediction of the reserve method. Several recent studies have shown that %Vo 2 max and reserve can differ in individuals who have low functional capacities (13,14). Malley et al. (14) found reserve to underpredict the measured energy cost of exercise in elderly men and women (mean age 64 ± 3 years) by 11 % at an intensity of 77% Vo 2 max. Belman and Gaesser (13) also reported reserve to underestimate %Vo 2 max for men and women 65 to 75 years of age. Their data show that at 53% and 75% of HRmax reserve, measured %Vo 2 max's were 72 and 82%, respectively. Badenhop et al. (12) studied subjects over 60 years of age and found that exercise at 57% and 70% of Vo 2 max corresponded to reserves of 30-45% and 60-75%. Jakicic and Donnelly (18) found that %Vo 2 max ranged from 67 to 85% in sedentary obese adults exercising at 70% of HRmax reserve. The present study is consistent with the results of these earlier studies on elderly subjects (12,13,14) and obese patients (18) and found that reserve can be considerably less than %Vo 2 max in men and women 60 to 80 years of age at exercise intensities between 53 and 88% of Vo 2 max. The disparity in the relationship between reserve and %Vo 2 max in the elderly may be due to the fact that cardiorespiratory fitness declines with age and inactivity (7,19). When prescribing exercise by the reserve method, resting HR represents an exercise intensity of zero. Oxygen uptake at rest, however, represents some proportion of Vo 2 max that is greater than zero. When resting energy expenditure represents a relatively high percentage of Vo 2 max, the reserve method can significantly underestimate the true energy cost of exercise. In young and middle-aged men of average or better fitness, resting Vo 2 represents less than 10% of Vo 2 max (7). Therefore, considering rest to represent zero exercise intensity has little influence on the relationship between %Vo 2 max and reserve in young and middle-aged adults. For subjects 67 to 89 years of age, however, resting Vo 2 may account for over 25% of the values reported for Vo 2 max (20). If a resting Vo 2 of 3.2 ml«kg" u min"' (21) is assumed for the subjects in the present study, resting Vo 2 would equal approximately 15% of Vo 2 max. This could also be true for other populations with relatively low aerobic capacities. Miller et al. (22) showed that estimated %Vo 2 max values (from reported prediction models) exceeded reserve values for 40 and 60% of HRmax reserve (%Vo 2 max = 53 and 66%) but not for 80% of HRmax reserve (%Vo 2 max = 79%) in obese men and women. To further compare %Vo 2 max with reserve in the elderly we estimated net exercise Vo 2 assuming a resting value for Vo 2 of 3.2 ml # kg" u min"' (21). When net exercise Vo 2 was estimated in the elderly subjects of the present study, reserve was still less than the calculated net %Vo 2 max by 9%, 9%, and 7% at 53%, 69%, and 88%, respectively. Therefore, consideration of resting Vo 2 accounts for some but not all of the difference between %Vo 2 max and reserve in elderly subjects. Another possible explanation for the disparity between the reserve and %Vo 2 max in the elderly may be due to the fact that the elderly trained on the treadmill prior to the submaximal test. This training period served the purposes of adapting the subjects to a training bout of 20 minutes and also allowing for the determination of speed and grade which would elicit heart rates of 40, 60, and 80% of HRmax reserve. Although the subjects may have had some traininginduced adaptations such as an increase in arteriovenous oxygen difference during this time period, significant increases in Vo 2 max would seem unlikely due to the low intensity of exercise. Most of the subjects underwent their submaximal treadmill test within 2 weeks of starting to train. Preliminary data from our laboratory show that after 6 months of aerobic training the relationship between the reserve and %Vo 2 max does not improve significantly (23). After the 6 months of training the elderly subjects improved their Vo 2 max by 18% (21.0 to 24.8 ml«kg" u min"'). The exercise training reduced the reserve and %Vo 2 max at the three absolute work loads. However, the relationship between reserve and %Vo 2 max did not improve with the increase in Vo 2 max (23). Thus, the reserve method still overpredicted the energy cost of exercise. Because reserve and %Vo 2 max are more closely equated in younger persons, the data from this study suggest that the relationship between reserve and %Vo 2 max may change as people age.. Studies examining the relationship between and %Vo 2 max in young (8,24) and middle-aged adults (7) have found to overestimate %Vo 2 max. Fox et al. (24) found that 70% HRmax corresponded to 55-60% of Vo 2 max in young subjects. Davis and Convertino (8) studied young men (mean age 23.7 ± 2.6 yr) and found overestimated %Vo 2 max by 22%, 16%, and 8% at 45%, 64%, and 78% Vo 2 max, respectively. Based on these

M170 PANTONETAL. and similar studies, the method has been considered too conservative for prescribing exercise training intensity in both cardiac patients and healthy adults (25). It has been recommended that 10 to 15 beats/min should be added to the training HR calculated by the HRmax method (1,10). Few studies have evaluated the relationship between and %Vo 2 max in older adults. Malley et al. (14) found that was 82% at 77% of Vo 2 max, an overestimation of 5%. The present study found to overestimate %Vo 2 max by 12% and 6% at 53% and 69% of Vo 2 max, but did not differ at 88% of Vo 2 max. Because the HRmax method does not correct for resting HR, it may be more appropriate to use for elderly individuals who have low Vo 2 max values. Increasing Vo 2 max by aerobic training may change the relationship between reserve and %Vo 2 max and between and %Vo 2 max in the elderly. The study by Jakicic and Donnelly (18) indirectly supports this idea. Again, they found that %Vo 2 max ranged from 67 to 85% in sedentary obese adults at 70% of reserve. Following a 90-day weight reduction program, the corresponding range for %Vo 2 max at 70% of HRmax reserve was reduced from 67-85% to 58-75%. These data suggest that improvements in cardiorespiratory function due to weight loss decrease the difference between reserve and %Vo 2 max. It is possible that increased fitness following aerobic exercise training would also decrease the difference between reserve and %Vo 2 max but perhaps increase the difference between and %Vo 2 max. However, preliminary data from our laboratory following exercise training in the elderly suggest that this may not be the case (23). Prediction of %S/0 2 max in the elderly. The relationships between reserve and %Vo 2 max and between and %Vo 2 max in the present study were described by the calculations of multiple regression equations (Figures 2 and 3). These equations may be useful for estimating energy expenditure when exercise training intensity is prescribed for men and women 60 to 80 years of age by the HRmax and HRmax reserve methods. The slope and intercept of our and %Vo 2 max equation were similar to those of the regression equations presented by Londeree and Ames (9), and Franklin et al. (26). Londeree and Ames studied 26 men 20 to 45 years of age and reported a slope of 1.37 and intercept of-41% Vo 2 max. Franklin et al. (26) studied 42 sedentary women 29 to 47 years of age and combined their data with data from other studies on men. The results reported by Franklin et al. showed that the slopes of the regression equations ranged from 1.2 to 1.5 and the intercepts ranged from -24 to -52% Vo 2 max. These studies show remarkably similar regressions of %Vo 2 max on, despite differences in age, gender, and fitness levels of the subjects studied. The R 2 and SEE values for the present study and the studies by Franklin et al. (26) and Londeree and Ames (9) ranged from R 2 =.63 to.94 and 5.7% to 10.5%, respectively. Although the reported regression equations may be used to obtain a rough estimate of %Vo 2 max from and reserve in elderly men and women, consideration of the relatively high variability associated with the estimation is advised. SEE values of approximately 10% for both models limit their utility due to lack of accuracy. When accurate %Vo 2 max values are required, oxygen uptake should be measured. Rating of perceived exertion. The Rating of Perceived Exertion (RPE) scale and heart rate have been shown to be linearly related to each other and to work intensity across a variety of exercise modalities and conditions (7). The original scale was developed from young adults and when it was applied to persons of various ages, it was found that the linear relationship with work intensity existed at all ages, but heart rate was consistently lower at each older age increment (7). Our results show that RPEs of 11, 13, and 15 correspond to exercise intensities of approximately 53%, 69%, and 88% Vo 2 max. Consequently, most elderly participants should exercise within an RPE range of 11 (fairly light) to 15 (hard). This is remarkably similar to the recommended RPE range of 12 to 16 for healthy young exercisers (1), considering the dramatic changes in the relationships between HRmax, HRmax reserve, and Vo 2 max with age. Therefore, the RPE scale may be used to help establish an appropriate exercise intensity for elderly men and women. Summary. The present study found that reserve was significantly lower than %Vo 2 max at workloads between 53 and 88% of Vo 2 max, whereas was greater than %Vo 2 max at workloads of 53% and 69% of Vo 2 max in men and women 60-80 years of age. Moreover, reserve more closely approximates Vo 2 max than does reserve in untrained men and women 60 to 80 years of age. 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