Impact of Short-Term Continuous and Interval Exercise Training on Endothelial Function and Glucose Metabolism in Prediabetes

Abstract

Introduction. The impact of interval (INT) vs. continuous (CONT) exercise training on endothelial function in relation to glucose metabolism prior to clinically meaningful weight loss is unknown in adults with prediabetes. Methods. Twenty-six subjects with prediabetes (60±1 y; 33±1 kg/m2; 2-hr-PG OGTT: 145±7 mg/dl) were randomized to 60 min of CONT (n=12; 70% of HRpeak) or work-matched INT exercise training (n=14; alternating 3 min at 90 and 50% HRpeak) for 2 weeks. Aerobic fitness (VO2peak) and body composition (bioelectrical impedance) were assessed before and after training. Flow-mediated dilation (FMD) was measured during a 2 h 75 g OGTT (0, 60, and 120 min) to assess endothelial function. Postprandial FMD was calculated as incremental area under the curve (iAUC). Glucose tolerance and insulin were also calculated by iAUC. Fasting plasma VCAM, ICAM, and hs-CRP were also assessed as indicators of vascular/systemic inflammation. Results. Both interventions increased VO2peak (P=0.002) but had no effect on body fat (P=0.20). Although both treatments improved glucose tolerance (P=0.06) and insulin iAUC (P=0.02), VCAM increased (P=0.01). There was no effect of either treatment on ICAM, hs-CRP, or fasting as well as postprandial FMD. However, 57% of people improved fasting and iAUC FMD following CONT compared with only 42% after INT exercise (each: P=0.04). Elevated VCAM was linked to blunted fasting FMD after training (r=−0.38, P=0.05). But, there was no correlation between fasting FMD or postprandial FMD with glucose tolerance (r=0.17, P=0.39 and r=0.02, P=0.90, respectively) or insulin iAUC following training (r=0.34, P=0.08 and r=0.04, P=0.83, respectively). Conclusion. Endothelial function is not improved consistently after short-term training, despite improvements in glucose and insulin responses to the OGTT in obese adults with prediabetes.

Metformin May Contribute to Inter-individual Variability for Glycemic Responses to Exercise

“…Although recent work suggests that interval exercise improves flow-mediated dilation (FMD), which measures large conduit arteries, more than continuous exercise in sedentary people (11,12,75) not all studies agree (76). Interestingly, we recently studied the effect of interval vs. continuous exercise on fasting and post-prandial arterial stiffness as well as endothelial function as measured by FMD in older adults with prediabetes (77,78). We found that 2 weeks of high intensity interval or moderate continuous exercise reduced post-prandial arterial stiffness but had no overall effect on fasting or post-prandial FMD.…”

“…We found that 2 weeks of high intensity interval or moderate continuous exercise reduced post-prandial arterial stiffness but had no overall effect on fasting or post-prandial FMD. Nonetheless, when examination of responder compared with non-responder analysis was performed, it was shown that continuous exercise elicited a 57% response rate to raise FMD compared with only 42% with interval exercise ( 78 ). This latter finding is consistent with work showing that either a single bout or short-term exercise training at moderate continuous intensity can promote vasodilation after glucose-induced insulin stimulation in adults with and without T2D ( 79 – 82 ).…”

A single bout of exercise improves vascular insulin sensitivity in adults with obesity

“…After 5 minutes, the cuff was deflated, and images were quickly acquired to capture post-ischemic flow velocity (four images). Images of post-ischemic vessel diameter were then recorded every 10 seconds for a total of 2 minutes (22,31).…”

“…However, the effects of acute exercise on vascular insulin sensitivity in conduit arteries and/or skeletal muscle capillaries are less known. Work by our group (22) and others (23) have used an oral glucose tolerance test to stimulate endogenous insulin production for examination of blood vessel function following acute or short-term training. However, these results are confounded by exogenous glucose fluctuations, incretin hormones, and/or neurological factors that prohibit understanding of direct insulin effects.…”

Considerations for Maximizing the Exercise “Drug” to Combat Insulin Resistance: Role of Nutrition, Sleep, and Alcohol

“…Using the FITT principle (i.e., frequency, intensity, time, and type) [ 48 ], we encourage readers to review work on exercise intensity and time (i.e., duration) which has been discussed extensively elsewhere [ 49 , 50 , 51 ]. Of note, while high-intensity interval training (HIIT) improves insulin resistance (via HOMA-IR assessment) in MetS patients [ 52 ], several studies show that when energy expended is matched between low to high exercise intensity conditions, no additional effects are observed on insulin action or endothelial function [ 53 , 54 , 55 , 56 , 57 ]. This suggests that differences in energy balance, not intensity per se, may account for such greater improvements in insulin sensitivity.…”