Effects of High-Intensity Intermittent Training on Endurance Performance
Sportscience 5(1), sportsci.org/jour/0101/cf.html, 2001 (1715 words)
Reviewed by John A Hawley, RMIT University, Melbourne, Australia
For an athlete to compete successfully in an endurance event, a maximum oxygen uptake (VO2max) of at least 70 ml.kg-1.min-1 is a minimum requirement (Hawley et al., 1997). While athletes employ a variety of training strategies to increase VO2max, recent research suggests that a form of interval training known as high-intensity intermittent training leads to rapid improvements in VO2max and endurance performance.
Researchers from Canada’s McMaster University recently investigated the effects of interval exercise on VO2max (MacDougall et al., 1998). Training was performed on a stationary cycle ergometer for three days each week. The program began with four intervals lasting 30 s, separated by a 4-min rest period. By Week 7 the number of intervals had increased to 10, while the rest intervals were gradually reduced to 2.5 min. VO2max increased by 9%, demonstrating that significant gains in VO2max could be achieved from exercise of a relatively short duration. In the first week of the program, each training session lasted 14 min. By Week 7, the length of each training session had increased to 30 min.
A team from Japan’s National Institute of Fitness and Sport found that a high-intensity intermittent training program achieved bigger gains in VO2max than a program of steady cycling (Tabata et al., 1997). Active male subjects were assigned to one of two groups, each training 5 days per week for 6 weeks. One group followed a training program involving 60 min of moderate intensity exercise (70% VO2max), for a total of 5 hours per week. The VO2max in this group improved by an average of 9%. Training sessions of the other group consisted of eight all-out work bouts, each lasting 20 s, with 10 s of rest. This group cycled for a total of only 20 min per week, yet their VO2max improved by 15%,
In addition to its effect on VO2max, high-intensity intermittent training can improve athletic performance. Lindsay et al. (1996) reported that 4 weeks of interval training can improve 40-km time trial performance of competitive cyclists. The cyclists replaced approximately 15% of moderate intensity endurance training with high-intensity intermittent training, completing six interval sessions during the course of the study. Each interval session consisted of six to eight 5-min work bouts at 80% of peak power, separated by 60 s of recovery. The authors found significant improvements in 40-km time trial performance (54.4 ± 3.2 vs 56.4 ± 3.6 min) and time to fatigue at 150% of peak power (72.5 ± 7.6 vs 60.5 ± 9.3 s).
In a similar study, Stepto et al. (1999) examined the effect of five different types of interval training on performance of a 40-km time trial. The cyclists were assigned to one of five groups. Each group followed a different program, as shown in Table 1.
The cyclists replaced approximately 15% of their normal training with one of the interval exercise programs, completing six interval sessions over three weeks. Although the authors hypothesized that longer intervals would promote the greatest improvement in performance, the two programs providing the greatest gains in time trial speed were those with work bouts lasting 30 s and 4 min. The principle of specificity dictates that the body will adapt to the demands imposed upon it. The 4-min intervals were carried out at a pace similar to that of the time trial, and were expected to improve performance. A 40-km time trial depends almost entirely on energy provided by the aerobic system. Work bouts lasting 30 s depend primarily on anaerobic energy, and were not expected to enhance performance.
This paradox may be resolved by the findings of Rodas et al. (2000), who reported that a high-intensity intermittent training program increases oxidative enzyme activity in muscle. Rodas et al. evaluated changes in aerobic and anaerobic metabolism in active males following a short training program. Subjects performed two weeks of daily high-intensity intermittent training consisting of two 15-s all-out bouts separated by 45 s of rest, followed by two bouts of 30 s all-out sprints separated by 12 min of rest. Every two training sessions, an extra work bout was added. The last 3 sessions consisted of seven bouts of 15 s and seven bouts of 30 s. Maximum oxygen consumption increased from 57 ± 3 to 64 ± 3 ml.min-1.kg-1, and there were substantial increases in activity of citrate synthase (38%) and 3-hydroxyacyl-CoA dehydrogenase (60%). These changes in oxidative enzyme activity may increase the rate of fat oxidation and reduce carbohydrate oxidation. The subsequent reduction in the accumulation of hydrogen ions could improve endurance performance (Hawley et al., 1997).
It’s also interesting to note that an increase in training intensity can improve endurance performance without a change in VO2max. Acevedo and Goldfarb (1989) tracked a group of trained male distance runners who increased their training intensity to 90-95% maximum heart rate for 8 weeks. There was an average 63 s reduction in 10-km race time and a significant decrease in plasma lactate at 85 and 90% of VO2max, but no substantial change in VO2max (65.3 ± 2.3 vs 65.8 ± 2.4 ml.kg-1.min-1).
Although these studies provide evidence that high-intensity intermittent exercise can increase VO2max and improve endurance performance, the different work and rest ratios make it difficult for an athlete or coach to design an effective training routine. Furthermore, a periodized training schedule is likely to be more effective than a continuous program of high-intensity intermittent exercise. Hawley et al. (1997) suggested that a year-round training program should consist of three main phases. Phase one is performed during an athlete’s non-competitive period, and consists of several months of moderate intensity, long duration exercise (60 min or more per session). The athlete then enters Phase two, involving two interval sessions per week. These interval sessions can replace two of the moderate intensity workouts. The work bouts during these interval workouts should consist of an intensity corresponding to race pace. For example, Stepto et al. (1999) used a total of eight work bouts (all carried out at race pace) each lasting 4 min with rest intervals of 90 s. Phase three, which begins approximately 21 days prior to the race, involves high-intensity intermittent training at maximum effort. This type of training is performed up to three times per week, and can consist of up to 12 work bouts lasting 30 s, with rest intervals of 4-5 min (Stepto et al., 1999). Gaskill et al. (1999) have presented evidence of the effectiveness of this kind of periodized program. In their study, cross-country skiers who had shown little improvement in competitive performance after a year of high-volume low-intensity training made substantial gains in the following year, when high-intensity intervals were phased in and the volume of low-intensity training was reduced.
The studies discussed in this article have used high-intensity intermittent exercise as a training intervention. However, the protocols varied widely. Some work intervals last between 15 and 30 s, while rest periods span 10 s to 4.5 min. More research is needed to establish the most effective form of interval training required to improve endurance performance.
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