Great HIIT Article
“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.”
Anyone who has tried them both will tell you that 30 seconds “all-out” with 4 minutes rest is a walk in the park compared to the Tabata protocol. Four minutes allows almost complete recovery—and time to renew enthusiasm for another very hard 30 seconds. The heart of the Tabata protocol is the 10-second rest interval, which allows partial recovery at best. That’s the idea; incomplete recovery makes each rep harder than the last, and brings you to the point of exhaustion on the last rep. Seven or eight reps and you’re done, literally.
The longer rest period in the study under discussion was probably a drawback in terms of effectiveness. On the other hand, the three-day-a-week frequency was very likely an advantage. (The Tabata protocol was done Monday through Friday with no rest days between exercise bouts.)
As noted above, the 20:10 work-to-rest ratio in the Tabata study produced substantial improvement in both aerobic and anaerobic work capacity, while the 30-second:4-minute ratio failed to produce improvement in either category. As explained in article 10, the reason almost certainly lies in the degree of overload. The Tabata protocol overloaded both aerobic capacity and anaerobic capacity to the max, while the work-rest ratio in the present study--the much longer rest periods in particular--probably produced a sub-maximum overload.
In a later study, Dr. Tabata compared the original protocol with an interval program very similar to one under discussion. Each subject did 4-5 bouts of 30 seconds, with 2-minute rest periods, to exhaustion. Tests showed that the 20-second intervals, with 10 seconds rest, overloaded both aerobic capacity and anaerobic capacity maximally, while the longer interval protocol, with two-minute rest periods, did not. In both respects, the stress produced by the second protocol fell well short of maximum.
But why? Why did the original protocol stress both aerobic and anaerobic capacity maximally, when the more intense (200% VO2max vs. 170%) and longer (30 seconds vs. 20) bouts of the second protocol did not? Dr. Tabata and his colleagues believe the key factor was the difference in the rest periods.
The relatively long 2-minute rest periods allowed oxygen uptake to fall considerably and, therefore, when the next exercise bout started there was a delay before the oxygen uptake increased and began again to approach maximum. On the other hand, the short 10-second rest periods allowed only slight recovery, and therefore oxygen uptake increased in each succeeding bout, reaching maximum capacity in the final seconds of the last bout. The same was true for anaerobic energy release. The 2-minute rest periods stopped the buildup of lactate and allowed the resynthesis of phosphocreatine (see article 7, Diet & Nutrition, on creatine) to occur. Again, the short rest periods in original protocol caused the oxygen deficit to continue building from rep to rep, reaching maximum anaerobic capacity at the end of the exercise.
Almost surely, that's why the current study failed to show improvement in aerobic and anaerobic capacity. The 4-minute rest periods allowed almost complete recovery and maximum stress was never achieved.
On the other hand, the one or two days rest between workouts probably gave the current study a leg up on the original Tabata protocol. The researchers believed that the rest days would be an important advantage. “The importance of rest days between sprint training sessions was emphasized in a recent study that showed that peak and mean power elicited were unchanged after 14 consecutive days of sprint training; however, when subjects performed the same number of training sessions over 6 weeks, with 1-2 days of rest between training sessions, power output improved significantly,” they wrote in the study report. “Although numerous mechanisms could potentially be involved, the importance of rest days between training sessions may be related in part to the fact that strenuous exercise leads to inactivation of cation pumps, and it has been speculated that up to several days may be required for normalization of sarcoplasmic reticulum Ca2+ pump function.” Simply put, it takes a day or two for muscles to recharge after very intense exercise.
So, it’s possible that Dr. Tabata and his colleagues could have achieved even better results by allowing their athletes a day or two to recover between workouts.
Another advantage of the interval protocol under discussion is that more people are likely to be willing to do intervals with 4-minute rest periods than with 10-seconds. Both protocols are obviously hard, but the less demanding regimen probably has wider appeal. It might turn more couch potatoes into gym rats.
Words to the Wise
As noted above, interval sprints are not for everyone--certainly not for people just getting started or those with health problems. If you have doubts, by all means talk it over with your doctor.
Frankly, I enjoy high-intensity intervals; they're challenging and leave no time for boredom. Not all the time, however. I make it a point to vary the work-rest ratio and cycle my training. I don't train all-out all the time.
Generally, short hard intervals with long rest periods are recommended to improve anaerobic capacity; and repetitions with short rest periods are suggested to overload the aerobic system. The Tabata research and the current study suggest that intensity--not volume--is the key to success.
It’s important to start a new regime at a manageable pace and ramp-up over time as your condition improves. When you top out, change the plan and start over.
Train smart and keep in mind that you usually get out of a program about what you put into it. That doesn’t mean more is better, however. As the current study demonstrates, stress and rest are both important.
Good training. :cool:
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