The aim of the present study was to examine if diabetes in the absence of neuropathy affects the exercising capacity of IDDM patients, and whether regular, intense training has a beneficial effect on endothelial function. Five groups of subjects were studied: 23 healthy control subjects who exercised regularly (age 33 ± 6 years), 23 nonneuropathic type 1 diabetic patients who exercised regularly (age 33 ± 6 years, IDDM duration 11 ± 8 years), 7 neuropathic type 1 diabetic patients who exercised regularly (age 36 ± 7 years, IDDM duration 22 ± 8 years), 18 healthy subjects who did not exercise regularly (age 34 ± 7 years), and 5 nonneuropathic type 1 diabetic patients who did not exercise regularly (age 31 ± 4 years, IDDM duration 20 ± 3 years). All groups were matched for age, sex, and body weight. No differences existed in the energy expenditure per week in physical activity among the three exercising groups or between the two nonexercising groups. The maximal oxygen uptake was similar between control and diabetic nonneuropathic exercisers, and among diabetic neuropathic exercisers, control nonexercisers, and diabetic nonexercisers; however, a significant difference existed between the first two and the last three groups (P < 0.0001). A stepwise increase was found in the resting heart rate among the groups, ranging from the lowest in control exercisers to the highest in diabetic nonexercisers, but the maximal heart rate was lower only in diabetic neuropathic exercisers compared with all other groups (P < 0.05). Assessments of endothelial function in both macro- and microcirculation were performed in 12 control exercisers, 10 diabetic nonneuropathic exercisers, 5 diabetic neuropathic exercisers, 17 control nonexercisers, and 4 diabetic nonexercisers. When all diabetic patients were considered as one group and all control subjects as another, the microcirculation endothelial function in the diabetic group was reduced compared with the control subjects (91 ± 49 vs. 122 ± 41% flux increase over baseline; P < 0.05). In contrast, no differences existed among the three diabetic groups or between the two control groups. Similarly, in macro-circulation, a reduced response during reactive hyperemia was observed in the diabetic patients compared with control subjects (7.0 ± 4.5 vs. 11.2 ± 6.6% diameter increase; P < 0.05), whereas again no difference existed among the three diabetic groups or between the two control groups. These data suggest that diabetes per se does not affect aerobic exercise capacity (Vo2max) in physically active individuals, but is reduced in the presence of neuropathy. In addition, regular exercise training involving the lower extremities does not improve the endothelial function in the micro- and macrocirculation of the nonexercised upper extremity in type 1 diabetic patients.

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