Effect of intensity of aerobic training on VO2max.

Gormley SE, Swain DP, High R, Spina RJ, Dowling EA, Kotipalli US, Gandrakota R.
Med Sci Sports Exerc. 2008 Jul;40(7):1336-43.

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. 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.

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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).

... groups: 1) moderate intensity (50% VO2R), 2) vigorous intensity (75% VO2R), 3) near-maximal intensity (intervals at 95% VO2R), and 4) nonexercising control.

DISCUSSION

The main finding of the study was that higher intensities of exercise elicit greater improvements in VO2max than lower intensities of exercise over a 4- to 6-wk training period in healthy, young adults. This finding is consistent with the original hypothesis. Unlike VO2max, there were no changes observed in resting HR and resting BP after training.

A study recently published by Helgerud et al. (16) examined the effects of 8 wk of aerobic endurance training at various exercise intensities in healthy, young-adult males. Groups performed running at a moderate-intensity (70% HRmax for 45 min each session), vigorous-intensity (85% HRmax for ~24 min per session), and two maximal-intensity interval training regimens that both alternated 90-95% HRmax with 70% HRmax, one using multiple 15-s intervals and one using four 4-min intervals. Both interval training groups significantly increased VO2max, whereas neither continuous training group did. Using a previously published formula, the moderate- and vigorous-intensity groups of Helgerudet al. were exercising at ~47% and ~72% HRR, respectively, which are comparable to the current study. The failure of the continuous training groups of Helgerud et al. to increase VO2max was probably due to their high baseline fitness, which averaged 58 mL/min/kg. Esfarjani and Laursen (11) recently compared interval training at VO2max with continuous training at 75% HRR in male runners. As in the study of Helgerud et al., the subjects’ baseline VO2max was greater than 50 mL/min/kg, and only the interval group increased VO2max. Both of these studies differed from the current study in the population (only males vs both males and females; high vs average fitness) and the mode of exercise (running vs cycling).

It should be noted that although interval training groups spend some of their training time at a very high intensity, a similar amount of time is spent at a lower intensity, and therefore the mean intensity of training may not be any higher than that of a continuous training program. In the current study, the interval training group used 5 min each for the work and the recovery phases of the intervals and had an average intensity of 72% HRR, which is slightly less than the 75% HRR of the vigorous group. The work–recovery periods of Helgerud et al. were 4 min at ~93% HRmax and 3 min at 70% HRmax, for a mean intensity of 83% HRmax in the interval group, whereas one of the continuous groups used 85% HRmax. Warburton et al. used 2 min at 90% HRR and 2 min at 40% HRR for the work and the recovery phases, yielding a mean intensity of 65% HRR in the interval group, and had the continuous training group use 65% HRR. Wisloff et al. used 4-min work phases at ~93% HRmax and 3-min recovery phases at 60% HRmax, for a mean intensity of 79% HRmax in the interval group, and used ~73% HRmax in the continuous training group. Despite the similarity of mean intensity between the interval and the continuous training groups, the interval groups in all of these studies experienced greater improvements in aerobic fitness after training. Therefore, although intensity is a key variable in cardiorespiratory training (as shown by comparing the two continuous training groups in this study), the mean intensity may not be as important as the highest intensity that is used for a significant portion of the training. A topic for future research is to determine what portion of training should be done at high intensities and using what work–recovery periods to obtain the greatest results.