David P. Swain

Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise

SUMMARYThe purpose of this Position Stand is to provide guidance to professionals who counsel and prescribe individualized exercise to apparently healthy adults of all ages. These recommendations also may apply to adults with certain chronic diseases or disabilities, when appropriately evaluated and

Heart rate reserve is equivalent to%??VO2Reserve, not to%??VO2max

Percentage of heart rate reserve (%HRR) is widely considered to be equivalent to % of maximal oxygen consumption (%VO2max) for exercise prescription purposes. However, this relationship has not been established in the literature, and a theoretically stronger case can be made for an equivalency between %HRR and %VO2 Reserve (%VO2R) (i.e., the difference between resting and maximal VO2). The current study hypothesized that %HRR is equivalent to %VO2R, not %VO2max, and that the discrepancy between %HRR and %VO2max would be inversely proportional to fitness level. Sixty-three adults performed incremental maximal exercise tests on an electrically braked cycle ergometer. HR and VO2 at rest, at the end of each stage of exercise, and at maximum were used to perform linear regressions on %HRR versus %VO2max, and %HRR versus %VO2R for each subject. For %HRR versus %VO2max, the mean intercept and slope were -11.6 +/- 1.0 and 1.12 +/- 0.01, respectively, which were significantly different (P < 0.001) from 0 and 1, respectively. For %HRR versus %VO2R, the mean intercept and slope were -0.1 +/- 0.6 and 1.00 +/- 0.01, respectively, which were not distinguishable from the line of identity. There was a significant (P < 0.01) inverse relationship between fitness level (VO2max) and the discrepancy between %HRR and %VO2max. In conclusion, %HRR should not be considered equivalent to %VO2max. Rather, %HRR is equivalent to %VO2R, and this relationship should be used in exercise prescription.

Effect of Intensity of Aerobic Training on VO2max

PURPOSE To determine whether various intensities of aerobic training differentially affect aerobic capacity as well as resting HR and resting blood pressure (BP). METHODS Sixty-one health young adult subjects were matched for sex and VO2max and were randomly assigned to a moderate- (50% VO2 reserve (VO2R), vigorous (75% VO2R), near-maximal-intensity (95% VO2R), or a nonexercising control group. Intensity during exercise was controlled by having the subjects maintain target HR based on HR reserve. Exercise volume (and thus energy expenditure) was controlled across the three training groups by varying duration and frequency. Fifty-five subjects completed a 6-wk training protocol on a stationary bicycle ergometer and pre- and posttesting. During the final 4 wk, the moderate-intensity group exercised for 60 min, 4 d.wk the vigorous-intensity group exercised for 40 min, 4 d.wk and the near-maximal-intensity group exercised 3 d.wk performing 5 min at 75% VO2R followed by five intervals of 5 min at 95% VO2R and 5 min at 50% VO2R. RESULTS VO2max significantly increased in all exercising groups by 7.2, 4.8, and 3.4 mL.min.kg in the near-maximal-, the vigorous-, and the moderate-intensity groups, respectively. Percent increases in the near-maximal- (20.6%), the vigorous- (14.3%), and the moderate-intensity (10.0%) groups were all significantly different from each other (P < 0.05). There were no significant changes in resting HR and BP in any group. CONCLUSION When volume of exercise is controlled, higher intensities of exercise are more effective for improving VO2max than lower intensities of exercise in healthy, young adults.

VO(2) reserve and the minimal intensity for improving cardiorespiratory fitness.

PURPOSE The American College of Sports Medicine has stated that aerobic training needs to occur at a minimum threshold intensity of 50% VO(2max) for most healthy adults and at 40% VO(2max) for those with a very low initial fitness. Recently, the concept of VO(2) reserve (%VO(2R), i.e., a percentage of the difference between maximum and resting VO(2)) has been introduced for prescribing exercise intensity. This analysis was designed to determine the threshold intensity for improving cardiorespiratory fitness expressed as %VO(2R) units. METHODS Previous studies in healthy subjects (N = 18) that evaluated the results of training at low-to-moderate intensities (i.e., < or = 60% VO(2max)) were identified. The original studies described the intensity of exercise variously as %VO(2max), %HRR, %HR(max), or as a specific HR value. In each case, the intensity was translated into %VO(2R) units. RESULTS Exercise training intensities below approximately 45% VO(2R) were consistently ineffective at increasing VO(2max) in studies that used subjects with mean initial VO(2max) values > 40 mL x min(-1) x kg(-1). In studies using subjects with mean initial VO(2max) values < 40 mL x min(-1) x kg(-1), no intensity was found to be ineffective. For this latter group of subjects, the lowest intensities examined were approximately 30% VO(2R). CONCLUSION Although evidence for a threshold intensity was not strong, this analysis of training studies supports the use of 45% VO(2R) as a minimal effective training intensity for higher fit subjects and 30% VO(2R) for lower fit subjects.

Target heart rates for the development of cardiorespiratory fitness.

The American College of Sports Medicine (ACSM) recommends the use of 40%, 60%, 80%, and 85% of maximal oxygen consumption (VO2max) as target values in developing exercise prescriptions. Further, the ACSM states that 55%, 70%, 85%, and 90% of maximal heart rate (HRmax) may be used as indices of these respective levels of % VO2max for the general population. The current study evaluated this relationship between %HRmax and %VO2max in apparently healthy, young adults. Eighty-one men and 81 women between the ages of 18 and 34 engaged in an incremental exercise test to exhaustion. Linear regressions of %HRmax and %VO2max were performed on each subject. From these regressions, target values of %HRmax were computed for each individual. Mean percentages of HRmax were 63%, 76%, 89%, and 92% at 40%, 60%, 80%, and 85% of VO2max, respectively. At all of these values of %VO2max, the values obtained for %HRmax were significantly greater (P < 0.001) than those used by the ACSM. Fitness affected these results, particularly among men. High fit men averaged 2% higher in %HRmax than low fit men at any given value of %VO2max.

Relationship between % heart rate reserve and % VO2 reserve in treadmill exercise

For exercise prescription purposes, it is often assumed that % heart rate reserve (%HRR) provides equivalent intensities to %VO2max. However, a recent study from this laboratory demonstrated that during cycling exercise %HRR is not equivalent to %VO2max, but is instead equivalent to a percentage of the difference between resting and maximal VO2, i.e., % VO2reserve (%VO2R). The current study examined these relationships during treadmill exercise. Fifty adults performed Bruce protocol treadmill tests to exhaustion. For each subject, data obtained at rest, at the end of each stage, and at maximum were used to determine linear regressions of %HRR versus %VO2max, and of %HRR versus %VO2R. For %HRR versus %VO2max the mean intercept and slope were -6.1+/-0.7 and 1.10+/-0.01, respectively, with a mean r of 0.990+/-0.002. For %HRR versus %VO2R, the mean intercept and slope were 1.5+/-0.6 and 1.03+/-0.01, respectively, with a mean r of 0.990+/-0.002. Both regressions differed statistically from the line of identity (i.e., intercept of 0 and slope of 1). However, the regression of %HRR versus %VO2R was significantly closer (P < 0.001 ) to the line of identity than was the regression of %HRR versus %VO2max. We conclude that %HRR should be considered as an indicator of %VO2R, not %VO2max, when prescribing treadmill exercise, as was previously concluded for cycling exercise.

The influence of body mass in endurance bicycling

Bicycling is a complex sport in which an athletes energy cost is related to two principal forces: air resistance when traveling on flat terrain, and gravity when traveling uphill. Both wind tunnel data and physiological measurements suggest that air resistance scales as body mass to about the 1/3 power. Thus, large cyclists have only slightly greater frontal drags than small cyclists. If expressed relative to body mass, the frontal drag of small cyclists is considerably greater than that of large cyclists. The difference in frontal drag (energy cost) is not made up for by the advantage to small cyclists in relative VO2max (energy supply), since the mass exponent for drag (1/3) is closer to zero than that for VO2max (2/3). Thus, small cyclists should be at a disadvantage in flat time trials, which field data support. The energy cost of riding uphill slightly favors the large cyclist, because the weight of the bicycle represents a relatively smaller load than it does to a small cyclist. The mass exponent is 0.79. Since this exponent is greater than that for VO2max, the small cyclists have an advantage in climbing, which is supported by field data.

A model for optimizing cycling performance by varying power on hills and in wind

The effect of varying power, while holding mean power constant, would have on cycling performance in hilly or windy conditions was analyzed. Performance for a 70-kg cyclist on a 10-km time trial with alternating 1-km segments of uphill and downhill was modeled, with mean VO2 (3, 4, 5 L.min-1), variation in VO2 (5, 10, 15%), and grade (0, 5, 10, 15%) used as independent variables. For the conditions of 4 L.min-1, 10% variation, and 10% grade, results were as follows: finishing time of 22:47.2 with varied power, versus 24:20.3 at constant power, for a time savings of 1 min 33.1 s. Separately, a 40-km time trial with alternating 5-km segments of headwind and tailwind (0, 8, 16, 24 km.h-1) was modeled, with the following results for the conditions of 4 L.min-1, 10% variation, and wind speed of 16 km.h-1: finishing time of 60:21.2 with power variation vs 60:50.2 at constant power, for a time savings of 29 s. Time saved was directly proportional to variation in VO2, grade, and wind speed and was indirectly proportional to mean VO2. In conclusion, the model predicts that significantly time savings could be realized on hilly and windy courses by slightly increasing power on uphill or headwind segments while compensating with reduced power on downhill or tailwind segments.

Is there a threshold intensity for aerobic training in cardiac patients

PURPOSE Recent guidelines have recommended the use of a percentage of oxygen uptake reserve (VO2R) for prescribing aerobic exercise intensity for cardiac patients. Moreover, these guidelines suggest that a threshold intensity may exist, below which no improvement in peak oxygen uptake (VO2peak) occurs. The purpose, therefore, was to translate the intensity of aerobic exercise in previous training studies using cardiac patients into %VO2R units, and determine whether a threshold intensity exists. METHODS Twenty-three studies, using 28 groups of aerobically trained cardiac patients, were identified in which VO2peak was measured before and after training by gas exchange. Intensity of exercise was variously described as a percentage of VO2peak, percentage of peak heart rate (HRpeak), percentage of heart rate reserve (HRR), or percentage of peak workload. These intensities were translated into equivalent units of %VO2R. RESULTS Of the 28 groups of patients, three failed to show significant improvements in VO2peak. These groups exercised at intensities corresponding to 47-55% of VO2R. However, six other groups exercised at comparable intensities (i.e., 42% to 55% of VO2R) and experienced significant increases in VO2peak. Other confounding variables in these studies were similar, including the initial VO2peak of the subjects, suggesting that the failure of three groups to significantly improve aerobic capacity was due to their small sample size. CONCLUSION No threshold intensity for aerobic training was identified in cardiac patients, with the lowest intensity studied being approximately 45% of VO2R. It is possible that intensities below this value may be an effective training stimulus, especially in extremely deconditioned subjects, but further research is needed to test that possibility and to determine whether a threshold exists.

Postprandial walking is better for lowering the glycemic effect of dinner than pre-dinner exercise in type 2 diabetic individuals.

OBJECTIVES In prior studies of exercise done before or after breakfast and lunch, postprandial activity generally reduces glycemia more than pre-meal. This study sought to examine the effects of exercise before or after an evening meal. DESIGN Examined the differing effects of a single bout of pre- or postprandial moderate exercise or no exercise on the glycemic response to an evening (dinner) meal in individuals with type 2 diabetes. SETTING Community-dwelling participants tested at a research university in Virginia. PARTICIPANTS Twelve men and women subjects (mean age of 61.4+/-2.7 years) with type 2 diabetes treated with diet and/or oral medications. INTERVENTION Three trials conducted on separate days consisting of a rest day when subjects consumed a standardized dinner with a moderate glycemic effect and 2 exercise days when they undertook 20 minutes of self-paced treadmill walking immediately before or 15 to 20 minutes after eating. MEASUREMENTS Blood samples taken every 30 minutes over a 4-hour period and later assayed for plasma glucose; from these data both absolute and relative changes in glucose levels were determined, as well as the total glucose area under the curve (AUC) of the 4-hour testing period. Initial samples were additionally assayed for glycated hemoglobin and lipid levels. RESULTS Twenty minutes of self-paced walking done shortly after meal consumption resulted in lower plasma glucose levels at the end of exercise compared to values at the same time point when subjects had walked pre-dinner. Total glucose AUC over 4-hours was not significantly different among trials. CONCLUSION Postprandial walking may be more effective at lowering the glycemic impact of the evening meal in individuals with type 2 diabetes compared with pre-meal or no exercise and may be an effective means to blunt postprandial glycemic excursions.