Mitchell H. Whaley

Physical fitness and clustering of risk factors associated with the metabolic syndrome.

PURPOSE The purposes of this study were to 1) assess the prevalence of clustering of metabolic markers of the MS in a defined population and 2) determine the association between CRF and such clustering in a large group of adult men (N = 15,537) and women (N = 3,899). METHODS Metabolic markers of the MS included systolic blood pressure (BP) > or = 140 mm Hg, serum triglycerides > or = 150 mg x dL(-1), fasting blood glucose > or = 110 mg x dL(-1), and elevated central adiposity (waist circumference > 100 cm). Cardiorespiratory fitness was defined as total time on a maximal treadmill exercise test. The cohort was grouped by the number of metabolic abnormalities and level of CRF. Associations between CRF and the number of metabolic abnormalities were assessed using proportional odds logit models. RESULTS Among men, the age-adjusted cumulative odds ratio for abnormal markers of the MS was 3.0 (95% C.I. 2.7-3.4; P < 0.001) for the least-fit men when compared with moderately-fit ones, and 10.1 (95% C.I. 9.1-11.2; P < 0.001) when compared with the most-fit men. Among women, the age-adjusted cumulative odds ratio was 2.7 (95% C.I. 2.1-3.5; P < 0.001) for the least-fit women when compared with moderately-fit ones, and 4.9 (95% C.I. 3.8-6.3; P < 0.001) when compared with the most-fit women. CONCLUSIONS These cross-sectional results suggest that low CRF is associated with an increased clustering of the metabolic abnormalities associated with the MS in both adult men and women and support the need for future prospective analyses.

Predictors of over- and underachievement of age-predicted maximal heart rate

The age-predicted maximal heart rate (PMHR) formula, 220--age, is frequently used for identifying exercise training intensity, as well as determining endpoints for submaximal exercise testing. This study was designed to identify variables discriminating those with actual maximal heart rates considerably above or below that predicted from the 220--age equation. Subjects included 2010 men and women ranging in age from 14 to 77 yr. Stepwise discriminant analysis was performed using maximal heart rate error groups as the dependent variable, and selected preexercise test characteristics as predictors. The HR error groups were based on the difference between the measured and PMHR as follows: below (> or = 15 beats.min-1 below PMHR), within (+/- 14 beats.min-1 of PMHR), and above (> or = 15 beats.min-1 above PMHR). A contrast of the below and above groups identified age, resting HR, body weight, and smoking status as predictors of group membership (P < 0.01) for both men and women. The overall canonical correlation was 0.282 and 0.294 for the men and women, respectively. Older age, higher resting HR, lower weight, and non-smoking were related to the above group, while the inverse was related to the below group. Standardized coefficients suggest that age and resting heart rate for the men, and age and smoking status for the women were the most potent variables for discriminating extreme deviations between measured and PMHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Validity of rating of perceived exertion during graded exercise testing in apparently healthy adults and cardiac patients.

PURPOSE Recent exercise guidelines recommend a generalized rating of perceived exertion (RPE) range of 12 to 16 (15-point Borg scale) as the perceptual range associated with a physiological training effect. However, whether an individual who selects an RPE within the generalized range during an graded exercise test or exercise training, is actually within the correlated physiological range (50 to 85% maximum oxygen consumption [VO2max]) has not been studied in large samples of apparently healthy individuals or cardiac patients. The purpose of the present study was to assess the validity of the generalized RPE recommendations in a large heterogeneous group of apparently healthy subjects and cardiac patients. METHODS Subjects included apparently healthy adults (N = 463) and cardiac patients (N = 217) who presented for a sign-symptom limited maximal graded exercise test (SSLMGXT). Ratings of perceived exertion associated with relative exercise intensities of 60 and 80% of maximal heart rate reserve (MHRR) and peak exercise were selected for analyses. RESULTS Significant interindividual variability in RPE was observed at both relative exercise intensities (6 to 20 RPE range at 60% MHRR; 8 to 20 RPE range at 80% MHRR) for both populations. Thirty-nine percent of healthy subjects and 32% of cardiac patients reported an RPE outside an 11 to 14 range at 60% of MHRR, whereas 32% of healthy subjects and 52% of cardiac patients reported an RPE outside of a 14 to 17 range at 80% of MHRR. Peak RPE was higher for the apparently healthy subjects compared with the cardiac patients (18.8 +/- 1.2 versus 16.5 +/- 1.8; P < 0.01). CONCLUSIONS These results challenge the applicability of the generalized RPE recommendations described in recent exercise guidelines under typical clinical exercise testing conditions. The basis for the generalized RPE recommendations warrant further investigation. Those who desire to use RPE as a marker of relative exercise intensity during SSLMGXT should take into consideration the large interindividual variability in these measures.

Evaluation of a new standardized ramp protocol: the BSU/Bruce Ramp protocol.

BACKGROUND Because of recent technological advances, exercise testing laboratories now have the ability to use ramp protocols with treadmill exercise tests. Since the Bruce protocol is the most widely used treadmill protocol in clinical laboratories, a standardized ramp treadmill protocol was developed that corresponds to the speed and grade settings of the Bruce protocol at each 3-minute time interval. The purpose of this study was to evaluate the utility of using subject demographic and exercise test data to predict peak oxygen uptake (VO2peak) for tests conducted with the BSU/Bruce Ramp protocol. METHODS Maximal exercise tests were performed by 698 men and women using the BSU/Bruce Ramp protocol. Peak oxygen uptake was measured during all tests. Stepwise multiple regression analyses were used to predict VO2peak (mL.kg-1.min-1) from maximal treadmill test time and selected variables including age, gender, physical activity habits, and body weight. RESULTS Maximal test time was found to be the most potent predictor of VO2peak, accounting for 86% of the variance in peak aerobic power, with a standard error of estimate of 3.4 mL kg min-1. A multiple regression equation including age, gender, physical activity habits, and body weight resulted in a slightly improved prediction (R2 = 0.88; standard error of estimates = 3.1 mL kg min-1). CONCLUSIONS Peak oxygen uptake values can be predicted with reasonable accuracy from the BSU/Bruce Ramp protocol. The BSU/Bruce Ramp would be an excellent choice for laboratories desiring to use a ramp treadmill protocol because of the design of the protocol with identical workloads at equivalent time periods (3, 6, 9, 12, 15, 18, 21 minutes) as the commonly used Bruce protocol.

Evaluation of the ACSM submaximal ergometer test for estimating VO2max.

The purpose of this investigation was to assess the reliability and validity of maximal oxygen uptake estimates (ESTmax) from the ACSM submaximal cycle ergometer test. Subjects included 15 men and 15 women aged 21-54 yr who performed two submaximal tests and one maximal cycle ergometer test to determine maximal oxygen uptake (VO2max). During the submaximal tests, heart rates (HR) were recorded from a radio telemetry monitor. ESTmax was predicted for both submaximal trials by extrapolating HR to an age-predicted maximal HR. Correlation coefficient and standard error of measure (SEmeas) for ESTmax between submaximal trials were r = 0.863 and SEmeas = 0.40 l.min-1, while a t-test revealed no significant difference between trials. Although trial means were not significantly different, large variation in individual cases was evident by the high SEmeas (0.40 l.min-1) and by a large SEmeas expressed as a percentage of the mean (13%). The mean of the two ESTmax significantly overestimated measured VO2max with percent error, total error, and mean error equal to 25.7%, 0.89 l.min-1, and 0.63 l.min-1, respectively. The standard error of estimate expressed as a percentage of the mean was equal to 16% and 15% for both ESTmax. In summary, the ACSM protocol failed to be reliable as represented by the large differences found between submaximal trials. Furthermore, the protocol significantly overestimates VO2max and should not be used when an accurate assessment of VO2max is required.

Failure of predicted VO2peak to discriminate physical fitness in epidemiological studies

Previous investigators reported that peak oxygen uptake (VO2peak) could be accurately predicted from nonexercise test variables, and that this score would be suitable for categorizing cardiorespiratory fitness (CRF) within epidemiological studies. However, the accuracy of these models has varied considerably. The purposes of this study were: 1) assess the accuracy of predicting VO2peak with a new nonexercise model, and 2) assess the utility of the predicted VO2peak for categorizing CRF in epidemiological studies. Subjects included 2,350 men and women. Cross-validated multiple regression models revealed that age, sex, resting heart rate, body weight, percentage body fat, smoking, and physical activity were significant predictors (P < 0.001) of VO2peak. The multiple regression model for relative VO2peak (ml.kg-1.min-1) had R2 = 0.733 (SEE = 5.38), whereas the model for absolute VO2peak (l.min-1) had R2 = 0.773 (SEE = 0.425). The 95% confidence intervals for the predicted VO2peak were large (+/- 10.6 ml.kg-1.min-1 and +/- 0.833 l.min-1). These results support the notion that VO2peak can be predicted from a multiple regression model devoid of exercise test variables. However, due to the extreme variability in the predicted scores, the regression models were unable to effectively distinguish CRF categories. Therefore, despite statistical success in predicting VO2peak for the nonexercise test regression models, we conclude that such models fail to provide the accuracy needed for categorizing CRF within large epidemiological cohorts where the purpose is to assess mortality risk.

Exercise prescription using resting heart rate plus 20 or perceived exertion in cardiac rehabilitation.

PURPOSE For patients starting a cardiac rehabilitation program, exercise intensity often is set 20 beats per minute above the standing resting heart rate (RHR+20) or in a range of 11 to 13 on Borgs Scale for Rating of Perceived Exertion (RPE 11-13). The purpose of this study was to determine the actual exercise intensity, expressed as a percentage of peak oxygen uptake reserve (%VO2R) using these techniques. METHODS For this study, 11 new referrals to a phase 2 cardiac rehabilitation program voluntarily underwent a symptom-limited exercise test and a field test that consisted of self-paced over-the-ground walking for 10 minutes at levels corresponding to RPE 11-13 and RHR+20. During both tests, gas exchange data were obtained via the Cosmed K4b and heart rate via the Polar monitor. RESULTS The mean %VO2R at RHR+20 (41.8 +/- 12.3%) and RPE 11-13 (71 +/- 15.3% mL.kg.min) were significantly different. Exercise at RHR+20 resulted in 4 of the 11 patients (36%) exercising at less than 40% VO2R, 6 of the patients (55%) exercising at 40% to 60% VO2R, and 1 of the patients (9%) exercising at more than 60% VO2R. Exercise at RPE 11-13 resulted in 1 of the 11 patients (9%) exercising at less than 40% VO2R, 1 of the patients at exercising at 40% to 60% VO2R (9%), and 9 of the patients (82%) exercising at more than 60% VO2R. CONCLUSIONS The results of this study indicate that using RHR+20 or RPE 11-13 to prescribe exercise intensity during over-the-ground walking for phase 2 cardiac rehabilitation patients results in substantial intersubject variability and raises questions about the safety and efficacy of these approaches.

Epidemiology of Physical Activity, Physical Fitness and Coronary Heart Disease

Observational population-based studies have consistently shown an inverse dose-response gradient between physical activity or fitness and coronary heart disease. This relationship is more firmly established in men. Existing studies suggest that the physical activity gradient, and perhaps the fitness gradient, is produced by a combination of varying levels of both the intensity and the amount of habitual physical activity. It is not at present possible to definitively describe the dose-response association between the intensity of physical activity and the risk of coronary heart disease. An answer to this important question awaits further research.

Reliability of perceived exertion during graded exercise testing in apparently healthy adults.

PURPOSE Ratings of perceived exertion (RPE) are widely used for monitoring individuals during graded exercise testing. Studies of the reliability of RPEs across various exercise conditions have produced mixed results. The purpose of this study was to assess the reliability of RPEs during graded exercise testing by comparing the perceptual-physiological relationship between the Bruce and Balke treadmill protocols throughout a broad range of relative exercise intensities. METHODS Thirty-eight middle-aged men and women completed two maximal treadmill graded exercise testing separated by 48 hours. Test order was randomly assigned. RPEs were compared across protocols and between gender at selected exercise intensities using a series of two-way analysis of variances with repeated measures. RESULTS A comparison of RPEs (Borg 15-point scale) during the graded exercise testing revealed significant protocol and gender differences at 40%, 60% and 80% of maximal heart rate reserve. RPEs were significantly higher during the Balke protocol compared to the Bruce at each intensity (45% = 9.5 +/- 2.0 vs. 8.3 +/- 1.6; 60% = 12.7 +/- 2.4 vs. 11.1 +/- 2.3; 80% = 15.7 +/- 2.2 vs. 14.1 +/- 2.0). In addition, men rated each intensity significantly higher than the women (P < 0.05). CONCLUSIONS The results from the present study confirm that the perceptual-physiological relationship observed during graded exercise testing varies as a function of the treadmill protocol employed and that these differences extend throughout the exercise training intensity range (40--80% of maximal heart rate reserve) recommended for healthy adults. The perceptual differences between the protocols could not be accounted for by any of the physiological measures assessed within the study. These results have implications when using RPEs from exercise testing for exercise prescription purposes.

High Cardiorespiratory Fitness Levels Slow the Decline in Peak Heart Rate with Age.

INTRODUCTION Although it is well accepted that peak HR (HRpeak) decreases with age, there is no clear consensus on the rate of this decline and the influence of cardiorespiratory fitness (CRF) on the rate of decline. METHODS Treadmill cardiopulmonary exercise test (CPET) results with RER ≥ 1.0 from participants (1849 men and 1469 women; 18-80 yr) of a university-based health assessment/fitness program were retrospectively examined using cross-sectional and longitudinal study designs. All subjects were free of overt cardiovascular disease and were not taking HR-altering medications. Only subjects having completed ≥ 2 cardiopulmonary exercise tests with ≥ 1 yr between test dates were included in the longitudinal analysis (418 men and 225 women). Subjects were categorized into CRF categories (high, moderate, and low) relative to age and gender normative classifications. A general linear-model univariate analysis was performed to test the effect of CRF on the decline in HRpeak with age. RESULTS In both cross-sectional and longitudinal analyses, HRpeak declined at a significantly faster rate across the CRF categories (cross-sectional: -0.60, -0.78, and -0.87 bpm · yr(-1), respectively; longitudinal: -0.61, -0.82, and -1.02 bpm · yr(-1), respectively). CONCLUSIONS This study provides evidence that the maintenance of a high or moderate CRF may slow the age-related decline in HRpeak in both men and women. The application of CRF-specific HRpeak prediction equations should be used to improve interpretation of HRpeak from exercise tests.