Insulin resistance is increasingly being linked to the development of Western lifestyle diseases including obesity and type 2 diabetes. Exercise appears to have both acute and chronic effects on insulin sensitivity. In particular both resistance training and endurance training have been shown to have insulin sensitising effects. This may explain the ability of exercise to prevent long term weight gain. Much of the work of exercise affecting insulin resistance has been performed on animals and so its relevance to humans has been questioned. However, humans studies have tended to corroborate the results of animal studies suggesting that mammalian insulin resistance shares common mechanisms between humans and animals. For example, a single bout of prolonged endurance exercise of 30 to 60 min at roughly 60 to 70 % of maximum oxygen consumption (just above comfortable pace) can significantly lower plasma glucose levels due to contraction stimulated translocation of GLUT4 glucose transporters to the cells surface.
This effect can increase the glucose transport in insulin resistant skeletal muscle cells. However, there is also a longer term effect of exercise on insulin sensitivity and this may relate to cellular signalling changes. In particular, the membrane bound glucose transport system may upregulate in insulin resistant cells, and this may include increased expression of GLUT4 transporters and increased expression of insulin receptor substrate-1. This increases the whole body glucose disposal, and this in turn lowers whole body glucose levels1. Resistance training also appears to be effective at improving insulin sensitivity, particularly in those who may have developed insulin resistance. For example, in one study2 researchers assessed the effects of twice weekly resistance training on subjects with type 2 diabetes. Following 4 weeks of training the strength of the subjects had increased in both their legs and arms. In addition, subcutaneous and visceral abdominal fat had decreased (by about 10 %).
There was a concomitant increase in insulin sensitivity in the resistance trained subjects that equated to around 46 %. However, there was no weight loss, despite the fact that they lost body fat. This suggests that the muscle mass of the subjects increased. Other studies have shown that resistance training might increases insulin sensitivity because it increases the total amount of skeletal muscle. In contrast, endurance training does not increase skeletal muscle mass but increases the oxidative capacity of the muscle present, and it is this that may improve the sensitivity of the muscle tissue. However, in reality there may be some crossover between resistance training and endurance training because both oxidative and non-oxidative fibre types can increase following resistance training. In resistance training, higher reps utilising a lower percentage of the 1 rep max may therefore be superior to heavier weights with lower reps with regard making improvements in insulin resistance.
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