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
