Most people understand and appreciate that physical activity is generally a good thing for health and wellbeing. The reality is, though, that many of us are quite sedentary. And a big reason for this relates to time, and specifically our sometimes perception that that there are, really, not enough hours in the day. However, there is some evidence that significant benefits can be had from really quite short periods of strenuous activity. For instance, I previously reported on a study which found that shorts bursts of ‘sprinting’ on an exercise bicycle brought similar fitness benefits of more leisurely cycling, in less than a quarter of the total exercise time [1].
In this particular study, individuals engaging in the ‘high intensity interval training’ (HIT) sprinted on a exercise bike with maximum effort for 30 seconds at a time with 4 mins of rest in between. 6 sessions were performed over a two-week period, with 4-6 ‘sprints’ in each session. I was interested to read a recently published study which used an identical exercise schedule. The focus here was not on fitness benefits, but on the impact HIT might have on individuals’ ability to handle sugar [2].
Sugar handling was assessed in this study with an ‘insulin glucose tolerance test’. Here, individuals have blood glucose and insulin levels measured, after which they are given a 75 gram dose of glucose. After this, glucose and insulin levels are monitored at intervals for two hours. These tests can allow estimates to made of the total amounts of glucose and insulin that appear in the bloodstream in response to the glucose loading dose. These measurements also can be used to calculate ‘insulin sensitivity’ (the ability of insulin to lower blood sugar levels appropriately). After a loading dose of glucose, lower levels of sugar and insulin mean greater insulin sensitivity.
The subjects in this study were 16 young (average age, 21), sedentary men. In these men, the prescribed exercise regime led to reductions in glucose and insulin levels of 12 and 37 per cent respectively. Insulin sensitivity improved by 23 per cent. All these improvements were statistically significant.
The authors of this study speculate about how HIT might bring these sorts of benefits. High intensity exercise is known to increase the breakdown of glycogen (a storage form of carbohydrate) in the muscles. The breakdown of glycogen can lead, subsequently, to enhanced uptake of glucose into the muscles. This mechanism, at least in part, might explain how vigorous activity may help in the regulation of sugar and lower insulin levels in time.
Whatever the mechanism, what it clear from this study is that it is possible for individuals to improve insulin sensitivity with high-intensity but short-duration exercise. The implication here is that such a regime may be of benefit for individuals with a tendency towards insulin sensitivity issues (insulin resistance) i.e. those with type 2 diabetes or at risk of this condition. The authors call for further studies in these individuals. The evidence as it stands suggests that high-intensity interval training shows considerable promise as a time-efficient way of getting considerable health benefits from exercise.
References:
1. Gibala M J, et al. Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol 2006;575(3)901-911
2. Babraj JA, et al. Extremely short duration high intensity training substantially improves insulin action in young sedentary males BMC Endocrine Disorders 2009;9:3
Excellent article! Very interesting indeed. Remember people are reading but don’t often have time or take the time to comment. Love your articles. Keep up the good work!
Interesting post. I really don’t like high intensity work-outs. I’d rather take a long walk than a short run. But the HIIT as described might be very do-able. And worthwhile. I’ll give it a shot. Thank you.
“In these men, the prescribed exercise regime led to reductions in glucose and insulin levels of 12 and 37 per cent respectively.”
Is that all? I got a 57% reduction in glucose (8.7mmol/L down to 3.7mmol/L) by taking 5,000iu/day Vit D3 without exercising.
There is an interesting discussion of this in the comments at:
http://conditioningresearch.blogspot.com/2009/01/intervals-dont-take-longand-can-prevent.html
Great blog, Dr John. Some 5/6 years ago I was diagnosed as T2 diabetic. No meds were prescribed. Not unsurprisingly when I made changes to my diet to one of reduced the glycemic load and took exercise my blood glucose (and one would also infer insulin levels) stabilised significantly. Arguably, either one of these lifestyle changes would be beneficial but there is also a likely synergistic effect in their combination.
Purely of anecdotal interest is the way I developed and tended towards a style of exercise training. Generally, I either swam or used the aerobic equipment at my local gym (cycle, row, x-trainer, treadmill, stepper etc.). I would do try to use several items of equipment in any given session but would impose a self designed regime on each which involved beginning and finishing at moderate intensity but with one or more bursts of high intensity (determined by high heart rate) while on that piece of equipment in a manner often referred to as interval training.
I used to say then that the ‘high intensity workouts’ ‘seemed to kick-start my metabolism’ – what’s more I used to feel that they really paved the way for glycemic control and that I could ‘bank’ my accumulated exercise sessions to good effect in a manner akin to regularly depositing money in a savings account. Now I believe firmly in the value of the metabolic pathways opened up by a healthy and regularly exercised muscle-mass.
It is a good thing that studies are beginning to investigate this part of the puzzle. Lets hope it all becomes clearer soon.
Clearly, there is more to good health and metabolism than can be expressed by the elegance of :-
C6H12O6 + (6) O2 –> (6) CO2 + (6) H2O + ATP
Willa Jean posted:
“I really don’t like high intensity work-outs. I’d rather take a long walk than a short run.”
Long walks will not cut it. I don’t like diabetes but I’m stuck with it and have to deal with it. The heart already does well in the long and slow endurance task. It never stops beating. To gain any benefit from excerise, the next step after getting of the couch is to add intensity to the program and get that heart rate pumped up so you can be rewarded with all the good that comes from it, ie/extended calorie burn and improved insulin response. The best way to add intensity is to do the same workout in less time, reduce rest periods. Later add some density to the workout- reduce time with longer distance, more reps or heavier weight and you are on your way. The Jane Fonda type work-out of long and slow is not going to do much after the first few weeks.
I am doing intervals on the treadmill, walking outside because I am obese, but I am hoping and surly am seeing signs, that it improves my insulin sensitivity. I take supplements for increasing insulin sensitivity plus my lower gi low carb diet I have been implementing. the treadmill is nice because I can use the rails to take weight off my ankles when they sometimes twinge with a little discomfort (I think a tendon doesn’t always slip properly) then they are okay, because of myweight I can take weight off them while still keeping my legs turnover very fast (for me anyway) and keeping my heartrate really high. I also have been lifting weights as well. I do my walking outside. I do hilly trails too to up my effort without pounding on my poor legs.
I am surly starting to see signs of improvement, tho I am still waking in the middle of the night with the shakes, and hunger, but hopfully this will pass in time, I hope. I have metabolic syndrome but my sugar is near normal when checked in glucose tolerance test. my a1c is coming down so far.
I have tried every diet under the sun, this is my last act of desperation, it seems I am on the right track, but it is too soon to tell.
rose