Seven days of aerobic exercise training improves conduit artery blood flow following glucose ingestion in patients with type 2 diabetes

Abstract

The vasodilatory effects of insulin account for up to 40% of insulin-mediated glucose disposal; however, insulin-stimulated vasodilation is impaired in individuals with type 2 diabetes, limiting perfusion and delivery of glucose and insulin to target tissues. To determine whether exercise training improves conduit artery blood flow following glucose ingestion, a stimulus for increasing circulating insulin, we assessed femoral blood flow (FBF; Doppler ultrasound) during an oral glucose tolerance test (OGTT; 75 g glucose) in 11 overweight or obese (body mass index, 34 ± 1 kg/m²), sedentary (peak oxygen consumption, 23 ± 1 ml·kg⁻¹·min⁻¹) individuals (53 ± 2 yr) with non-insulin-dependent type 2 diabetes (HbA1c, 6.63 ± 0.18%) before and after 7 days of supervised treadmill and cycling exercise (60 min/day, 60-75% heart rate reserve). Fasting glucose, insulin, and FBF were not significantly different after 7 days of exercise, nor were glucose or insulin responses to the OGTT. However, estimates of whole body insulin sensitivity (Matsuda insulin sensitivity index) increased (P < 0.05). Before exercise training, FBF did not change significantly during the OGTT (1 ± 7, -7 ± 5, 0 ± 6, and 0 ± 5% of fasting FBF at 75, 90, 105, and 120 min, respectively). In contrast, after exercise training, FBF increased by 33 ± 9, 39 ± 14, 34 ± 7, and 48 ± 18% above fasting levels at 75, 90, 105, and 120 min, respectively (P < 0.05 vs. corresponding preexercise time points). Additionally, postprandial glucose responses to a standardized breakfast meal consumed under "free-living" conditions decreased during the final 3 days of exercise (P < 0.05). In conclusion, 7 days of aerobic exercise training improves conduit artery blood flow during an OGTT in individuals with type 2 diabetes.

Trial registration: ClinicalTrials.gov NCT00972452.

Figures

Fig. 1.

Study design. A: continuous glucose monitoring (CGMS) was used to quantify postprandial glucose responses to a standardized breakfast meal in patients with type 2 diabetes (n = 11) before and during the final 3 days of a 7-day exercise training program (60 min/day, 60–75% HRR). B: glucose, insulin, and femoral blood flow (FBF) were assessed before and at 15-min intervals following an oral glucose tolerance test (OGTT) at baseline and after the exercise training program.

Fig. 2.

Glucose (A), insulin (B), and C-peptide (C) responses to 75-g oral glucose tolerance test in obese, sedentary volunteers with type 2 diabetes before (baseline) and after 7 days of aerobic exercise training (7d Exercise). D: Matsuda insulin sensitivity index (ISI), an estimate of insulin sensitivity calculated from glucose and insulin responses to the OGTT. *Significantly different from baseline (P < 0.05).

Fig. 3.

Absolute (A) and relative (%change from fasting; B) FBF following a 75-g oral glucose tolerance test in obese, sedentary volunteers with type 2 diabetes before (baseline) and after 7 days of aerobic exercise training (7d Exercise). *Significantly different from corresponding time point at baseline (P < 0.05).

Fig. 4.

A: mean postprandial glucose responses to a standardized breakfast meal in obese, sedentary volunteers with type 2 diabetes over 3 days before (baseline) and during the final 3 days of a 7-day aerobic exercise training program (7d Exercise). B: glucose AUC0–120; glucose area under the curve. *Significantly different from baseline (P < 0.05).