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“Scientific inquires are creating a new knowledge base and understanding of aerobic training and resistance training, and pointing towards potentially more optimal ways to train and…to more effectively and positively impact a myriad of health related mechanisms…For example, do we need to perform at least some aerobic training in a moderate, continuous way to affect mechanisms associated with diabetes [and other disease].” Richard A. Winett, PhD, Master Trainer, December, 2011
Short, Hard Intervals for Type 2 Diabetes
A pilot study from Canada found that brief, high-intensity intervals may very well be an effective and time efficient strategy for people with type 2 diabetes (T2D). “Our findings indicate that low-volume, high-intensity interval training can rapidly improve glucose control and induce adaptations in skeletal muscle that are linked to improved metabolic health in patients with type 2 diabetes (T2D),” Jonathan P. Little and colleagues wrote in the Journal of Applied Physiology (2011).
In a sharp departure from the norm, Little et al proposed that 60-second bouts of hard (not all-out) cycling interspersed by like periods of rest could be as good or better than continuous, low- to moderate-intensity exercise for T2D. What’s more, they proved it in only two weeks.
Researchers from McMaster University and the School of Health & Exercise Science at the University of British Columbia recruited eight volunteers with T2D (age ~ 63) to performed six sessions of high-intensity interval training (HIT) spread over two weeks. (10 times 60s cycling at roughly 90% of maximum heart rate with 60s rest) Before training and again from 48 to 72 hours after the last training session, glucose regulation was monitored continuously for 24 hours. Muscle biopsies were also taken before and 72 hours after the training ended to gauge changes in mitochondrial capacity.
Reduced mitochondrial capacity has been implicated in insulin resistance and T2D, the researchers explained; it seems that muscle oxidation capacity is a significant predictor of insulin sensitivity. Mitochondria convert fuel to energy with the aid of oxygen, so this is logical. Mitochondria oxidize calories that would otherwise show up in blood sugar count.
Perceived rate of exertion (PRE) and percentage of heart rate maximum indicate the degree of difficulty of the interval protocol. On a scale of 1 to 10, PRE rose on average from 5 after the first rep to 8 after the tenth rep. Heart rate gradually increased from the first interval to the last, from slightly under 80% to slightly over 90% of maximum. Importantly, total weekly training time (including warm-up, rest periods, and cooldown) was 50% lower than the 150 minutes of continuous exercise recommended by the American Diabetic Association. The protocol required only 10 minutes of hard work, comprising only 30 minutes of the 75-minute weekly total. Patients should be willing and able to follow, even enjoy, this interval protocol. (See my comments below)
“To our knowledge, this is the first study to examine the effects of HIT on glycemic regulation using continuous glucose monitoring,” the Little team emphasized in discussing the results, which were impressive.
“Average blood glucose concentrations…after the final training session were significantly lower than pretraining, indicating that… HIT improved glycemic control, particularly…after meals.” That’s good news for people with T2D, because “increasing evidence” suggests that controlling blood sugar levels after meals is as important, if not more important, than the more common fasting blood sugar readings.
As suggested above, people with insulin resistance and T2D have been shown to have reduced mitochondrial content and capacity. Having shown earlier that low-volume HIT increases mitochondrial capacity in healthy individuals, the researchers predicted that it would have the same effect on people with T2D. That proved to be the case. “Low-volume HIT was a potent stimulus to increase mitochondrial capacity in the current study," the researchers wrote, "as evidenced by increased enzyme activity…as well as elevated protein content….” Markers of the rate of growth in mitochondrial capacity increased between 20% and 369%, quite amazing after only two weeks of HIT.
“Our results suggest that low-volume HIT may be a viable, time-efficient strategy to improve health in patients with T2D,” the researchers wrote. This is great news for those who have T2D, and those who want to guard against it. While bigger and longer studies are warranted, these findings are another giant step forward in the search for time-efficient and effective ways to stay fit and healthy.
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Most remarkable of all is that 60 minutes of hard training spread over two weeks provided around the clock benefits for two or three days after the last workout. Blood sugar was significantly reduced during several breakfast-lunch-dinner cycles. “Perhaps, a high level of physical activity…or constantly trying to be active isn’t as necessary as public health professionals would have us believe…if harder exercise training is engaged in several times per week,” my knowledgeable friend Dr. Richard Winett wrote in his Master Trainer newsletter. (Winett is also quoted at the top of this article.)
My concern, however, is that three hard interval sessions a week is too much for most people to sustain; they’ll do it—even enjoy it—under supervision (as in the Little study), but they’re not likely to keep doing it on their own. Hard training every workout is asking for trouble; it is neither fun nor productive. My own experience is that one or at most two hard interval workouts a week is all I can tolerate effectively, especially in the context of a balanced program of strength and aerobic training. Most people will, I believe, be happier with a program including resistance training, intervals, and walking or some other low-intensity activity. While that much variety may not be strictly necessary for health purposes, it is far more likely to be continued over time. Short walks speed recovery and make you more productive in day-to-day activities; you feel better after a walk, more energetic.
Variety is good for the body and the mind. No program will work unless we are willing to keep doing it.
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