Target-seeking behavior of plasma glucose with exercise in type 1 diabetes

OBJECTIVE - To investigate the reproducibility of the plasma glucose (PG) response to exercise in subjects with type 1 diabetes on a nonintensive insulin regimen. RESEARCH DESIGN AND METHODS - Subjects cycled for 45 min at 50% VO2max on two occasions (studies 1 and 2) either 1 h after lunch and usual insulin (protocol A) or after overnight fasting without morning insulin (protocol 13). Identical diet, activity, and insulin (twice daily neutral and intermediate) were maintained before and during each study day. A total of 13 type 1 diabetic subjects (6 men and 7 women, BMI 24.0 +/- 0.9 kg/m(2) [means +/- SE], age 42.6 +/- 2.7 years, diabetes duration 14.1 +/- 2.8 years) completed protocol A, and 7 (3 men and 4 women, BMI 25.8 +/- 1.3 kg/m(2), age 39.7 +/- 1.3 years, diabetes duration 14 +/- 4.4 years) completed protocol B. RESULTS - in protocol A (fed), the fall in PG during exercise was 4.5 +/- 1.0 and 5.0 +/- 0.8 mmol/l in studies 1 and 2, respectively, whereas in protocol B (fasted), it was 0.6 +/- 0.8 and 3.4 +/- 1.6 mmol/l. Regression analysis of the change in PG in protocol A in study 1 versus study 2 showed poor reproducibility (r(2) = 0.12, P = 0.25) despite uniform conditions. In protocol B, the fall in PG was more reproducible r(2) = 0.81, P = 0.006). In fed subjects, there was better (P = 0.01) and clinically useful reproducibility of the PG at exercise completion (r(2) = 0.77, P = 0.0001) compared with preexercise. CONCLUSIONS - These results indicate poor reproducibility of the change in PG during exercise after feeding in type 1 diabetes on nonintensive insulin regimens but reasonable reproducibility when fasting. Exercise apparently decreases the glycemic variability after feeding, so that PIS concentrations after exercise seek a reproducible "target." Thus, the absolute PG level after a typical bout of exercise in the fed state should be a good guide to carbohydrate or insulin adjustment on subsequent occasions.