Large Pre- and Postexercise Rapid-Acting Insulin Reductions Preserve Glycemia and Prevent Early- but Not Late-Onset Hypoglycemia in Patients With Type 1 Diabetes

OBJECTIVETo examine the acute and 24-h glycemic responses to reductions in postexercise rapid-acting insulin dose in type 1 diabetic patients.RESEARCH DESIGN AND METHODSAfter preliminary testing, 11 male patients (24 2 years, HbA(1c) 7.7 0.3%; 61 +/- 3.4 mmol/mol) attended the laboratory on three mornings. Patients consumed a standardized breakfast (1 g carbohydrate kg(-1) BM; 380 +/- 10 kcal) and self-administered a 25% rapid-acting insulin dose 60 min prior to performing 45 min of treadmill running at 72.5 +/- 0.9% VO2peak. At 60 min postexercise, patients ingested a meal (1 g carbohydrate kg(-1) BM; 660 +/- 21 kcal) and administered a Full, 75%, or 50% rapid-acting insulin dose. Blood glucose concentrations were measured for 3 h postmeal. Interstitial glucose was recorded for 20 h after leaving the laboratory using a continuous glucose monitoring system.RESULTSAll glycemic responses were similar across conditions up to 60 min postexercise. After the postexercise meal, blood glucose was preserved under 50%, but declined under Full and 75%. Thence at 3 h, blood glucose was highest under 50% (50% [10.4 +/- 1.2] vs. Full [6.2 +/- 0.7] and 75% [7.6 +/- 1.2 mmol L-1], P = 0.029); throughout this period, all patients were protected against hypoglycemia under 50% (blood glucose 3.9; Full, n = 5; 75%, n = 2; 50%, n = 0). Fifty percent continued to protect patients against hypoglycemia for a further 4 h under free-living conditions. However, late-evening and nocturnal glycemia were similar; as a consequence, late-onset hypoglycemia was experienced under all conditions.CONCLUSIONSA 25% pre-exercise and 50% postexercise rapid-acting insulin dose preserves glycemia and protects patients against early-onset hypoglycemia (8 h). However, this strategy does not protect against late-onset postexercise hypoglycemia.