“This has the potential to change the way we think about keeping fit. We thought there would be benefits but we did not expect them to be this obvious. It shows how effective short intense exercise can be”
~ Professor Martin J. Gibala (London Telegraph, June 5, 2005)
“Slowly, slowly the rest of world figures this out.” Laszlo Bencze
Sprints Build Endurance!
Tabata-type Training Takes Center Stage
Two Minutes Potent as Two Hours
Intensity Trumps Volume
My friend Richard Winett, PhD, publisher of Master Trainer, was one of the first in this country--perhaps the first--to write about Dr. Izume Tabata’s groundbreaking research published in 1996, on short, intense intervals. Dr. Tabata and his colleagues at the National Institute of Health & Nutrition, Tokyo, Japan, reported: "[Six to 8 very hard 20 second intervals with 10 second rest periods] may be one of the best possible training protocols…” Dr. Tabata told Dick Winett in a personal communication: "The rate of increase in VO2max [14% in only 6 weeks] is one of the highest ever reported in exercise science." What’s more, anaerobic capacity increased by a whopping 28%.
Several of the earliest articles on this website were about high intensity intervals for fitness and fat loss; articles 10 and 11 in our Aerobic Exercise category discuss Dr. Tabata’s research.
Because of my interest in high-intensity aerobics (I first wrote about it in Ripped 3), quite a number of people emailed about the recent research on sprint interval training done by Kirsten Burgomaster and colleagues at McMaster University, Hamilton, Ontario, Canada, and published in the Journal of Applied Physiology (June 2005).
In that study, sixteen active but untrained students, average age 22, were divided into two groups: eight who performed two weeks of sprint intervals, and eight controls who were tested before and after, but did no training.
The test group did four to seven “all-out” 30-second sprints on a bicycle ergometer with four-minute rest periods, six times over two weeks. (Dr. Tabata’s subjects did intervals five days a week for six weeks; the rest periods were much shorter, of course. We’ll discuss the differences in the two studies below.)
The muscles of the trained group showed substantial aerobic adaptation: 38% increase in citrate synthase, a mitochondrial enzyme that indicates the power to use oxygen, and a 26% increase in glycogen (muscle sugar) content. Interestingly, there was no change in peak oxygen uptake (VO2max) or anaerobic work capacity.
“Most strikingly,” the researchers wrote, “cycle endurance capacity increased by 100% after [sprint interval training].” The time to fatigue cycling at about 80% of VO2max increased on average from 26 minutes to 51 minutes!
The control group showed no change in any of the test parameters.
“To our knowledge, this is the first study to show that sprint training dramatically improves endurance capacity during a fixed workload test in which the majority of cellular energy is derived from aerobic metabolism,” the researchers reported. Impressively, the short period of very intense exercise produced improvements “comparable to or higher than previously reported aerobic-based training studies of similar duration.” In other words, about two minutes of very intense exercise (15 minutes over 2 weeks) produced the same or better results than previously shown after two hours a day at about 65% of VO2max, or 20 hours over two weeks.
Intervals for the Masses
Although in some ways less impressive the Dr. Tabata’s results (more later), the new study has created quite a stir, especially among health professionals eagerly looking for ways to motivate people to exercise.
Martin J. Gibala, an associate professor in the Department of Kinesiology at McMaster University and lead spokesman for the new study, has been quoted widely in this country, Canada and in the UK.
“The whole excuse that ‘I don’t have enough time to exercise’ is directly challenged by these findings,” Gibala told the London Telegraph. “This has the potential to change the way we think about keeping fit. We have shown that a person can get the same benefits in fitness and health in a much shorter period if they are willing to endure the discomfort of high-intensity activity.”
“This type of training is very demanding and requires a high level of motivation; however less frequent, high intensity exercise can indeed lead to improvements in health and fitness,” Gibala told CNN.
“We thought the findings were startling,” Gibala told CTV, Canada, “because it suggests the overall volume of exercise people need to do is lower than what’s recommended.” He added, “We think there might be a public health message that you can perform intense exercise, but less volume, and obtain similar benefits.”
The Journal of Applied Physiology found the new study noteworthy enough to merit a thought provoking “Invited Editorial” in the same issue by Edward F. Coyle, Department of Kinesiology and Health Education, University of Texas at Austin.
Not only is the study a “documented first,” Coyle writes, it “serves as a dramatic reminder of the potency” of intense exercise to improve performance, with “implications for improving health.” It shows that sprints are “very time efficient, with much bang for the buck.”
Challenge to Conventional Wisdom
It seems logical, says Coyle, that “aerobic endurance performance is only enhanced by aerobic endurance training, but it has been proven wrong in the realm of athletics as well as muscle biochemistry.” In short, prolonged low intensity exercise is not necessarily the best way to build endurance. Long slow running or biking may be a waste of time for people who want to become fit and healthy but have no plans to run a marathon or compete in high-level bicycle racing.
Coyle observes that middle-distance runners typically include sprint intervals in their training to improve aerobic endurance. “Indeed,” he writes, “it is likely that if an experienced runner or bicyclist had only 2 weeks and very limited time to prepare for a race of [about] 30-minutes duration, that sprint interval training would become a mainstay of their preparation.” Roger Bannister’s preparation to run the first 4-minutes mile is a classic case in point; see article 136 in our Aerobic Exercise category.
Coyle points to the recent popularity on “spinning” as an indication that the idea may be catching on in the general fitness population. “From the perspective of muscle biochemistry,” he adds, “it has long been recognized that 6-8 weeks of sprint interval training increases aerobic enzyme activity in muscle [citing several studies].”
Regarding the health implications, Coyle adds: “The large increase in citrate synthase activity in muscle implies that a host of adaptations typical of aerobic endurance training have been initiated, such as improved insulin action, improved lipoprotein lipase activity, and greater clearance of plasma triglycerides [citing studies].”
Referencing a research paper about the evolutionary underpinning of modern chronic diseases, Coyle suggests that sprint interval training might be an efficient way to keep our sedentary population from crossing “a biological threshold, beyond which chronic health conditions develop.” (See “Grow Or Decay, Your Choice,” # 146, Health and Fitness category.)
Energizing the Fibers
What accounts for the surprising effectiveness of very hard 30-second sprints in improving endurance capacity? It obviously works, but why? What’s the precise mechanism? The researchers offered a smorgasbord of possible mechanisms, but I found the explanation offered in the editorial more satisfying and quite logical.
“We can only speculate,” the researchers state, “but it is plausible that a training-induced increase in mitochondrial potential, as measured by citrate synthase maximal activity” is responsible for the improvement. Being good scientists, however, they go on to muddy the water, perhaps unnecessarily: “However, the precise mechanisms that regulate endurance performance are multifactorial and extremely complicated, and the data from other studies suggest that sprint training can stimulate a range of adaptations that might facilitate performance aside from changes in mitochondrial potential.” They then proceed to give a long list of possibilities that only an exercise physiologist would appreciate.
The editorial, on the other hand, goes for the jugular. Coyle says that both sprint interval training and prolonged sub-maximal aerobic exercise increase mitochondrial potential, but reminds us that the muscle fibers affected are different. The specific fibers affected probably explains why very brief sprint training proved to be as effective [or more effective] for improving endurance as much longer and less intense aerobic training, according to Coyle. “All-out sprint training especially stresses recruitment and adaptation of fast twitch muscle fibers that are remarkably and equally responsive as slow twitch muscle fibers in their ability to increase mitochondrial enzyme activity,” Coyle explains. “In fact, the low-intensity aerobic exercise that is typically prescribed for endurance training or health is not very effective at increasing aerobic activity in [fast twitch] muscle fibers, which comprise approximately one-half of the fibers within the muscles of most people,” he continues. “Thus low-intensity aerobic training is not a very effective or efficient method for maximizing aerobic adaptation in skeletal muscle because it generally does not recruit [fast twitch] fibers.”
In other words, sprint interval training increases the endurance capacity in all muscle fibers, fast and slow, while long slow training leaves half of the fibers unused and untrained. Makes perfect sense, doesn’t it? It’s like pulling the wagon with one horse, when two would get you a lot farther down the road. (See Ripped 2 for an explanation of the “all-or-none” law of muscle fiber recruitment, and The Lean Advantage (first volume) on the order in which muscle fibers, slow and fast, are recruited.)
A Price to Pay
There is no free lunch, of course. High-intensity intervals are hard. The editorial also addressed this issue. “[Repeated all-out sprints] cause a feeling of severe fatigue lasting for at least 10-20 minutes,” Edward Coyle writes. “That is the price for its effectiveness and remarkable time efficiency. It remains to be determined which population, depending on age, health status, and psychology, are most likely to adhere and benefit from sprint interval training.” The possibility of injury is also a factor to be considered. “Chance for impact injury during stationary cycling or swimming seems low and might be compared with sprint running,” Coyle suggests.
Recognizing that adherence and motivation would be an issue, the London Telegraph asked three “quite fit” employees of the Reebok Sports Club in Canary Wharf, London, to evaluate sprint intervals. As might be expected, reviews were mixed.
One eager beaver, 35, rode for 10 minutes in 60-second sprints. “It felt like I had just done an hour’s run,” he reported. “It was more than I was used to but I feel more exhilarated because it was so intense.”
“To be honest, it was not much fun and unless I was really pressed for time I would not change my exercise regime,” he added.
Another fellow, 23, tried the two minutes of cycling in 30-second super-bursts and found that he was exhausted. “It was torture, really, but I was amazed at how short a time it took me to tire myself out completely,” he related. “I didn’t enjoy it but it felt like it worked.”
The third guinea pig, 27, who rode for 45 minutes at a moderate pace, insisted that she had also received a good workout. She said, “I am not sure I would want to go through the pain of 30-second sprints.”
A fitness expert for Reebok, who had not tried the study protocol, thought that most people would not want to do it “because it is so uncomfortable, but for those willing to endure it would work.”
Finally, an Olympic triple jump gold medallist offered a more positive spin: “Going for a 40-minute run is not for everybody. The idea of going and doing a short intense workout would appeal to people and help them to embrace a healthier lifestyle.”