Regular physical activity has been shown to confer a protective effect against the development of diabetes, particularly in those individuals who are at greatest risk of developing the condition (62-65). For the obese individual who has already developed diabetes, regular physical exercise also has several clinical benefits. In any weight management programme, therefore, it is essential that consideration be given to increasing physical activity. Treatment strategies that combine physical activity with dietary changes are generally much more effective than treatments which are exclusive to one or other strategy (66). In general, any measure that increases modest daily activity, such as avoiding lifts, or getting off the bus one stop earlier, is beneficial in increasing energy expenditure. A sedentary obese individual performing 3 h of any activity standing up rather than sitting down will increase his 24-h energy output from 40% to more than 75% above the BMR (67). However, for the obese individual with Type 2 diabetes, increasing daily activity patterns may not be enough, and more intensive degrees of exercise need to be considered on an individual basis.
Physical activity has a positive effect on insulin action, thus improving glucose control and insulin sensitivity (68). In addition, exercise improves lipid profiles by reducing serum TG and VLDL and raising HDL concentrations. Improvements in blood pressure have also been observed, independent of weight loss. Cardiac fitness is improved, with the risk of myocardial infarction reduced by 35-50% (69). Evidence suggests that these benefits are not uniform and that, in general, younger (40-54 years) individuals with Type 2 diabetes, in the early stage of disease, are more likely to benefit from the effects of exercise (70). In addition, the greatest benefits from physical activity may be in the weight maintenance phase of obesity management (71).
The psychological benefits of exercise are equally important for the obese individual with Type 2 diabetes. Reductions in anxiety levels, improved body image and higher self-esteem promote greater self-efficacy and help the individual to cope with stressful situations which often result in overeating and relapses (71,72).
While exercise improves insulin action, the effects of physical training disappear within days when discontinued, so consideration must be given to the nature and duration of the activity. Programme activities need to be regular and of at least moderate intensity (73). Aerobic activities, e.g. walking, swimming, cycling, for 20-60 min at moderate or greater intensity for 3-4 days/ week will benefit glycaemic control and at least 5 days a week will assist weight loss (74,75). The value of walking as an exercise strategy for those with Type 2 diabetes should not be overlooked. Those asked to walk 10 000 steps a day, and maintain a 1000 kcal deficit diet, lost more weight and had greater improvements in insulin sensitivity than those on diet alone (76).
Unfortunately, obese persons with Type 2 diabetes identify more barriers to exercise than to any other aspect of the diabetes self-care regimen, with specific complaints of physical discomfort, fear of hypoglycaemia, being too overweight to exercise and lack of family support (77). Physical discomfort as a limiting factor has to be considered from the perspective of both obesity and diabetes. Obese women report higher degrees of perceived pain and exertion when walking than non-obese, suggesting that this moderate intensity activity is actually more intense for the obese due to the greater relative oxygen cost of walking (78). In addition, the myriad of macrovascular and microvascular complications associated with diabetes may increase discomfort during activity and limit endurance and flexibility (71). Patients with proliferative retinopathy or hypertension, for example, should avoid resistance training and high-intensity exercises and those with peripheral neuropathy are advised to pursue activities such as swimming, where the ankle and foot are not under stress. Advice regarding appropriate footwear, foot inspection and adequate hydration should be given and those at risk of hypoglycaemia should take care to adjust insulin doses and consume sufficient carbohydrates (79). The emergence of exercise referral schemes may be an important development for the treatment of obesity in Type 2 diabetes (1).
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