Effect of Intensity of Aerobic Training on VO2max

Shannan E. Gormley; David P. Swain; Renee High; Robert J. Spina; Elizabeth A. Dowling; Ushasri S. Kotipalli; Ramya Gandrakota

Disclosures

Med Sci Sports Exerc. 2008;40(7):1336-1343. 

In This Article

Abstract and Introduction

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 V˙O2max and were randomly assigned to a moderate- (50% V˙O2 reserve (V˙O2R), vigorous (75% V˙O2R), near-maximal-intensity (95% V˙O2R), 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-1 the vigorous-intensity group exercised for 40 min, 4 d·wk-1 and the near-maximal-intensity group exercised 3 d·wk-1 performing 5 min at 75% V˙O2R followed by five intervals of 5 min at 95% V˙O2R and 5 min at 50% V˙O2R.
Results: V˙O2max significantly increased in all exercising groups by 7.2, 4.8, and 3.4 mL·min-1·kg-1 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 V˙O2max than lower intensities of exercise in healthy, young adults.

The 1996 Surgeon General's Report recommended that Americans obtain at least 30 min of moderate-intensity physical activity, most days of the week, to maintain cardiovascular well-being.[36] The report also stated that a greater amount or a greater intensity of exercise confers greater benefits, but specifics for intensity were not provided. Recently, the American College of Sports Medicine and the American Heart Association recommended a minimum of 30 min of moderate-intensity physical activity 5 d·wk-1, 20 min of vigorous-intensity physical activity 3 d·wk-1, or a combination of the two.[15]

Research suggests that vigorous-intensity exercise (60-84% oxygen consumption reserve (V˙O2R)) results in greater increases in aerobic capacity than moderate-intensity exercise (40-59% V˙O2R).[32] Specifically, some training studies that have compared more than one intensity of continuous aerobic exercise while controlling the total volume or energy expenditure of exercise have found significantly greater increases in aerobic capacity in the higher-intensity group.[5,7,8,10,13,14,19,25,28] However, several similar studies found no difference between groups performing continuous exercise at different intensities.[3,4,6,9,12,16,20,21,22,30,31] Moreover, only a few studies have compared the effects of near-maximal-intensity exercise, which can only be performed using intervals, with continuous exercise of either moderate or vigorous intensities. Three studies found that such intervals were more effective than lower-intensity continuous training in cardiac patients.[27,37,38] Only two studies have compared near-maximal intervals with lower-intensity continuous training in healthy adults, and both studies included only highly fit males as subjects.[11,16] Both studies found significant increases in V˙O2max in the interval group and no increase in the lower-intensity continuous training groups, but it is not known if individuals of average fitness, and especially women, will respond similarly. Therefore, the current study aimed to confirm whether continuous exercise at a vigorous intensity is more effective than continuous exercise at a moderate intensity for improving aerobic capacity and also to determine whether interval training at a near-maximal intensity in a mixed-gender population of average fitness is more effective than continuous exercise of a lower intensity.

Vigorous-intensity exercise confers greater cardioprotective health benefits than moderate-intensity exercise, including a lower incidence of coronary heart disease that may be related to lower risk factors.[33] Clinical trials have found that higher-intensity exercise resulted in greater reductions in resting blood pressure (BP) than lower intensity,[3,19,24,35] although not all studies have found an intensity effect.[5]

A hallmark of endurance training is resting bradycardia.[29] However, few studies have evaluated the potential role of exercise intensity in reducing resting HR. One study that did not control the volume of exercise found that training at 72% of V˙O2R resulted in a significant decrease in resting HR, whereas training at 50% V˙O2R did not.[23] This finding is suggestive of an intensity effect, but because volume was not controlled, it is not conclusive. Only five studies that have controlled exercise volume between two groups exercising at different intensities measured resting HR.[5,13,22,24,35] Of these, only one found an intensity effect, in that women training at 64% V˙O2R decreased resting HR, whereas those training at 41% V˙O2R did not.[24] Men in neither intensity group decreased resting HR; however, there were few men in the study. Further research is warranted to fully examine the question of whether higher-intensity exercise is more effective at lowering resting BP and HR than lower-intensity exercise.

The primary purpose of this study was to determine whether various intensities of aerobic training differentially affect aerobic capacity in healthy adults. Some studies that have compared vigorous and moderate intensities of continuous exercise found that vigorous-intensity is more effective, but other studies have not. Moreover, research comparing near-maximal-intensity intervals with lower-intensity continuous training is limited to either cardiac patients or highly fit men. A secondary purpose of the study was to examine the effects of training intensity on resting HR and resting BP. It was hypothesized that there would be significantly greater increases in V˙O2max in the higher-intensity groups: near-maximal > vigorous > moderate > control. It was also hypothesized that there would be significantly greater reductions in resting systolic BP, diastolic BP, and HR in the higher-intensity groups: near-maximal > vigorous > moderate > control.

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