Exercise capacity with special reference to type 2 diabetes

Sammanfattning: Physical inactivity and obesity is a growing health problem world wide. Three different samples with a wide range of glucose tolerance were included in the thesis to represent a wider population. The exercise capacity was studied in one group of healthy sedentary middle aged men with normal glucose tolerance in study I and II. In a group of elderly men with normal glucose tolerance (NGT), impaired glucose tolerance (IGT) and with type 2 diabetes (T2D) was the influence of insulin sensitivity on exercise capacity studied (Study III). Exercise testing and exercise training in individuals with T2D was examined in a group of middle aged women with T2D in study IV and V. The performance of a maximal incremental cycle test in sedentary healthy male subjects was highly affected by lower extremity muscular strength and muscular endurance (Study I). Also upper body muscular strength correlated to exercise capacity as measured by cycle ergometry. When exercise capacity and muscular strength of the upper body increased in response to combined supervised group training, the correlation between muscular strength of the upper body and exercise capacity improved (Study II). Exercise capacity assessed during cycling was affect by whole body insulin sensitivity and the waist-hip ratio (Study III). Also, fibre type composition (Study I and III) and capillary density (Study III) contributed to peak exercise capacity. Estimation of VO2peak according to Åstrand sub-maximal exercise testing significantly overestimates directly measured VO2peak in women with T2D (Study IV). Improved insulin sensitivity appeared to be related to exercise intensity rather than duration, whereas improved HbA1c appeared to be related to exercise volume in T2D women (Study V). Though closely related, there may be different indices explaining VO2peak and WRpeak. Muscular strength and muscular endurance of not only the legs but also the arms and trunk may be important aspects of peak exercise capacity during a cycle test in healthy sedentary men. Exercise capacity is independently related to insulin sensitivity, muscle fibre composition and waist/hip ratio in subjects with NGT, IGT and T2D whom are matched for age and BMI. This suggests that metabolic abnormalities in skeletal muscle are of prime importance for the reduction in exercise capacity in over a wide range of insulin sensitivity. Sub-maximal tests should be used with caution in patients with T2D. Improvement in insulin sensitivity after six months combined supervised group training in female diabetic subjects is related to exercise intensity, whereas the reduction in HbA1c is related mainly to training volume. Metabolic effects of training may be seen in the absence of improved exercise capacity.