It is hard to fathom how beneficial very short, but highly intensive sprints of exercise can be, not only for your metabolic capacity (i.e. weight management), but also for muscle capacity, endurance and cardiovascular health. The below very interesting studies provide compelling evidence that there is no benefit in spending hours on the treadmill. Use your time wisely, and train intensively in short bursts at maximum capacity. This is what the Metabolic Circuit training model is all about.
On June 6, 2005, CNN reported on the startling (to some) findings of a McMaster University research group, proclaiming that "six minutes of pure hard exercise once a week could be just as effective as an hour of daily moderate activity"*
The study, published in the Journal of Applied Physiology, revealed that very intense exercise results in unique changes in skeletal, muscle and endurance capacity. Changes like these were believed to require hours of exercise each week. According to the “Methods” section of the study:
Sixteen healthy individuals volunteered to take part in the experiment. Eight subjects (including two women) were assigned to a training group and a preformed exercise test before and after 2-week sprint training intervention. Eight other men served as a control group and performed the exercise performance test 2 weeks apart with no training intervention. We also obtained needle biopsy samples from the training group to examine potential training-induced adaptations in resting skeletal muscle. We did not obtain biopsies from the control group for ethical reasons, because other studies have shown no change in resting muscle metabolite concentrations or the maximal activities of mitochondrial enzymes when control subjects are tested several weeks apart with no sprint training intervention. All subjects were recreationally active individuals from the McMaster University student population who participated in some kind of exercise two to three times per week (e.g., jogging, cycling, aerobics), but none was engaged in any sort of structured training program. After routine medical screening, the subjects were informed of the procedures to be employed in the study and associated risks, and all provided written, informed consent. The experimental protocol was approved by the McMaster University and Hamilton Health Sciences Research Ethics Board.**
The program required the subjects to perform either for or seven thirty-second bursts of "all-out" stationary cycling, followed by four minutes of recovery time, for a total of either two minutes or three and a half minutes of exercise. This was performed three times a week for two weeks, for a total of either six minutes or ten and a half minutes of exercise per week. At the conclusion of the study, when the subjects were retested, it was found that the endurance capacity in the "sprint" group increased by almost 100 percent (going from an average of twenty-six minutes to fifty-one minutes), whereas the control group (who weren't by any means inactive during this period, as they were jogging, cycling, or performing aerobics, as noted) showed no change. The muscles of the high-intensity-trained group also showed a significant increase in citrate synthase, an enzyme that is indicative of the tissue's power to use oxygen.
An editorial that accompanied the report of the study in the same issue of the journal offered this overview:
Recreationally active college students performed only 2-4 min of exercise per session and just six sessions over two weeks. The remarkable finding of this study was that this small total amount of very intense exercise training was sufficient to "double" the length of time that itense aerobic exercise could be maintained (i.e., from 26-51minutes).
Although peak oxygen uptake was not increased, aerobic adaptations did occur within active skeletal muscle as reflected by a 38% increase in activity of the mitochondrial enzyme citrate synthase.
This study is significant because it contains a "documented" first, and more importantly it serves as a reminder to the scientific community and society. It appears that this is the first scientific documentation that very intense sprint training in untrained people can markedly increase aerobic endurance and that the total "dose" of exercise over the 2-week period, performed in six sessions, amounted to only 15 min. This serves as a dramatic reminder of the potency of exercise intensity for stimulating adaptions in skeletal muscle that improve performance and have implications for improving health. In other words, we are reminded that intense sprint interval training is very time efficient with much "bang for the buck."
The findings of Burgomaster et al. challenge the concept that aerobic endurance performance is only enhanced by aerobic endurance training. On the surface, this concept seems logical, but it has been long ago been proven wrong both in the realm of athletics as well as muscle biochemistry.***
Given that the study was conducted at McMaster University, in Canada, Martin Gibala, one of its lead researchers, was sought out by national Canadian news network, CTV, for comment. "We thought the findings were startling," Gibala told CTV, "because it suggests the overall volume of exercise people need to do is lower than what's recommended.”****
A Second Study
Still, a hue and cry arose from the fitness world, and even from some parts of the medical world. After all, these results were obtained in contrast with a control group that did not perform any specialized "cardio" training. Certainly, if similar study were performed contrasting the benefits of the six-minute-per-week group with one that engaged in more traditional cardio modalities, the advantage would have to fall to the latter group.
Gibala and associates in fact went back into the lab and performed another study that tested and examined changes in exercise capacity (muscular endurance) as well as molecular and cellular adaptations in skeletal muscle after subjects performed either high-intensity exercise (what they deemed a low-volume sprint-interval training, or SIT, group) or a more conventional endurance exercise (what they deemed a high-volume endurance training, or ET, group).
This time, their study again involved sixteen subjects, the average age of which was twenty to twenty-two years. All of the subjects were tested to see how long it took them to cycle 18.6 miles on a stationary bike. The subjects were then split into two groups and made to exercise at either high intensity with a shorter volume or low intensity with higher volume, as determined by their maximum aerobic capacity (VO2 max). The first group performed high-intensity work on a stationary bike - thirty seconds of intense bike riding (at 250 percent of their VO2 max), followed by four minutes of rest. They repeated this procedure three to five times, until they had completed a total of two to three minutes of hard cycling. The second group took a more traditional approach, cycling at a moderate level (65 percent of VO2 max) for 90-120 minutes. Both groups were made to cycle on three nonconsecutive days per week for a total of three "workouts" a week, or six total “workouts” performed over a two-week period. This made for a total of six to nine minutes of actual training time per week for the high-intensity group, versus four and a half to six hours for the higher-volume group, or twelve to eighteen minutes of total exercise for the high-intensity group and between nine and twelve hours of total exercise for the conventional (or low-intensity/high-volume) group over the same two-week period. After the two weeks of the program had elapsed, both groups were made to repeat the initial 18.6-mile cycling test.
Despite the fact that the more conventional endurance exercise group spent 97.5% more time engaged in exercise, both groups of subjects were found to have improved to the same degree. Note that the group that exercised 97.5% more did not receive an equivalent benefit from having done so. In fact, they received "zero" additional benefit from all of the extra time they spent engaged in exercise. Even in terms of endurance benefit, when the researchers performed muscle biopsies and further tests to determine changes in the subjects' fitness levels at the end of the two weeks, these tests showed that the rate at which the subjects' muscles were able to absorb oxygen also improved to the same level. According to the experimenters:
Biopsy samples obtained before and after training revealed similar increases in muscle oxidative capacity, as reflected by the maximal activity of cytochrome c oxidase (COX) and COX subunits II and IV protein content (main effects, P 0.05), but COX II and IV mRNAs were unchanged. Training-induced increases in muscle buffering capacity and glycogen content were also similar between groups (main effects, P 0.05)....
This led the researchers to conclude:
Given the large difference in training volume, these data demonstrate that SIT is a time-efficient strategy to induce rapid adaptions in skeletal muscle and exercise performance that are comparable to ET in young active men.*****
In other words, there is no additional advantage in devoting hours per week to the pursuit of health and fitness improvement. Indeed, there is no additional physiological advantage afforded to one's body, including endurance or cardio benefits, by training that lasts more than six to nine minutes a week. Given the considerable wear-and-tear costs that attend exercise in general, particularly in activities such as running, the idea of increasing your risk of incurring such trauma is pointless from a health and fitness standpoint. The key findings in these studies indicate that in terms of overall health, a workout requiring six to nine minutes a week produced the same muscle enzymes (which are essential for the prevention of type 2 diabetes) as a workout requiring four and a half to six hours per week.
That is significant in light of the growing levels of unfitness. After the study Professor Gibala stated, "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."******
* CNN news story, June 6, 2005, http://edition.cnn.com/2005/health/06/06/sprint.training
** K.A. Burgomaster, S.C. Hughes, G.J.F. Heigenhauser, S.N. Bradwell, M.J. Gibala, "Six Sessions of Sprint Interval Training Increases Muscle Oxidative Potential and Cycle Endurance Capacity in Humans," Journal of Applied Physiology 98, no. 6 (June 1, 2005): 1985-90.
*** E.F. Coyle, "Very intense Exercise-Training Is Extremely Potent and Time Efficient: A Reminder," ibid., 1983-84
**** Professor Martin (M.J.) Gibala quoted from a CTV interview, ctv.ca/servlet/article news/story/ctvnews/1117489599756_13/?hub=health
***** M.J. Gibala, J.P. Little, M. Van Essen, G.P. Wilkin, K.A. Burgomaster, A. Safdar, S. Raha and M.A. Tarnopolsky, "Short-Term Sprint Interval Versus Traditional Endurance Training: Similar Initial Adaptions in Human Skeletal Muscle and Exercise Performance," Journal of Physiology 575 (2006): 901-11
****** Professor Martin (M.J.) Gibala quoted from a telegraph.co.uk article, http://telegraph.co.uk/news/main.jhtml?xml=/news/2005/06/05/nfit05.xml