High-intensity interval training is powerful and time-efficient training method to improve fitness and health. According to recent results high-intensity interval training is as effective as continous moderate intensity aerobic training to improve insulin-stimulated glucose uptake in skeletal muscles in middle-aged men, while neither of these training modes improved free-fatty acid uptake studied at resting baseline.
An interesting feature in that glucose uptake training adaptation was that improvement occured only in those skeletal muscles that had been actively engaged in exercise, which was cycling. Hence, insulin-stimulated glucose uptake increased only in quadriceps femoris muscle group, which is the main muscle group producing force in cycling. No change was observed in hamstrings, even if they are also engaged in cycling, let alone in arm musculature. This means that it is important to exercise as many muscles as possible in your training if you want to maximize particularly your whole body insulin sensitivity which is very important for metabolism and in the prevention of diabetes.
Another important training adaptation feature also was that maximal blood flow response in heart tended to be lower in high-intensity interval training group, while it tended to be improved by continous moderate intensity training in these middle-aged overweight men. This finding raises some questions regarding how healthy it is if previously untrained subject start to exercise heavily, but it needs to be studied whether lowered maximal cardiac blood flow is just a natural training response or something to be worried about.
Finally, a recent study has also elucidated that similar training that was just described above can improve insulin-stimulated glucose uptake in all muscles in case of diabetes. Thus, in contrast to healthy state, when insulin-stimulated glucose uptake is impaired, it can be increased by exercise training not only in muscles that have been actively trained, but also in those muscles that were not exercised. In diabetes also free-fatty acid uptake also improved, but only in quadriceps femoris muscle group. These findings highlight the role of exercise in improving health in healthy state, but particularly in diabetes.