Clinical ScienceMultiple short bouts of exercise over 12-h period reduce glucose excursions more than an energy-matched single bout of exercise
Introduction
Type 2 diabetes is characterized by repeated hyperglycemic periods throughout the day that can eventually result in numerous health complications. Increased physical activity has been shown to reduce these hyperglycemic excursions [1], and is known to reduce the risk of complications of type 2 diabetes. Muscle glucose transport and reduced insulin secretion are seen both acutely and chronically with physical activity in both lean and obese individuals with impaired fasting glucose concentrations [2], [3]. The reduced insulin demand is closely associated with the contraction-mediated GLUT-4 translocation in skeletal muscle, resulting in increased glucose uptake during and following exercise. One study demonstrated a 51% reduction in insulin concentrations, which corresponded with a 48% reduction in the secretory rate of insulin following an hour-long bout of low-intensity (40% VO2peak) exercise [4].
Recent investigations also point to the negative aspects of accumulating long periods of sedentary behavior regardless of adherence to physical activity guidelines, and recommend the use of short bouts of activity to break up sedentary periods throughout the day [5], [6]. An increased number of breaks in sedentary behavior, corresponding with short active bursts, are associated with reduced 2-h plasma glucose concentrations in middle-aged, healthy individuals following an oral glucose tolerance test [7]. Dunstan and colleagues [8] recently reported lower glucose and insulin responses to a single test drink in obese adults with the addition of light- and moderate-intensity walking during the 5 h testing period. These findings [7], [8] raised the question of whether short, frequent bouts of exercise would be more beneficial than 1-h of acute morning exercise in modulating insulin secretion and glucose excursions when multiple meals are consumed over the course of an entire day.
The purpose of this study was to determine the effect of exercise on glucose and insulin concentrations during a 12-h study period in obese individuals with impaired fasting glucose concentrations. It was hypothesized that 1-h of walking in the morning or accumulated through short, frequent bouts throughout the 12-h study period would attenuate glucose excursions and insulin secretion to multiple meals over the course of a day as compared to a sedentary condition. We also hypothesized that the short, frequent walking bouts would improve glucose control more so than the single 1-h exercise bout, and this would be independent of insulin concentrations. Further previous studies have only examined postprandial glucose or insulin responses to a single OGTT, and did not examine the hormone responses over the course of an entire day when multiple meals are consumed. Since the glucose and insulin responses to the first meal are not replicated in subsequent meals (known as the second-meal phenomenon) [9], [10], [11], and there is evidence that glucose tolerance [12], [13] exhibits diurnal patterns, it is possible that postprandial glucose and insulin responses may also demonstrate altered responses with subsequent meals, and that this response may be altered through various patterns of physical activity. This study allowed us to examine the hormonal response across a 12 h day, and with frequent blood sampling identify how responses differ with different exercise patterns.
Section snippets
Study subjects
All subjects completed a written informed consent document prior to participation in this study which was approved by the Syracuse University Institutional Review Board. Details of this study have been published previously [14]. Subjects were young (18–35 years old), obese (BMI > 30 kg/m2) individuals with impaired fasting glucose concentrations (> 5.55 mmol/L following a 12-h fast). Inclusion criteria were non-hypertensive; total cholesterol < 11.1 mmol/L and low-density lipoprotein cholesterol < 8.88
Subject Characteristics
Eleven subjects completed all study visits (3 women, 8 men). The mean age was 25 years, BMI 34 kg/m2, HOMA-IR 0.42 ± 0.12, and QUICKI 2.97 ± 0.10. Female subjects had a higher percent body fat (42.0% ± 3.3% vs. 28.9% ± 2.7%), total cholesterol (181 ± 2.4 vs. 127.3 ± 2.6 mg/dl) and LDL cholesterol (91.5 ± 10.2 vs. 51.3 ± 5.7 mg/dl) than male subjects (P < 0.05). The mean resting BP value across subjects was slightly elevated (122/68 mmHg) and the mean fasting blood glucose value was 6.3 ± 0.3 mmol/L. Across testing days,
Insulin Concentrations
Fasting insulin concentrations were not significantly different across conditions (Fig. 2A). In the SED condition, the 12-h insulin iAUC was higher (P < 0.05) compared to the INT and EX conditions. However, no significant differences were observed in the 12-h insulin iAUC response between the EX and INT conditions (P = 0.13). Examining the 2-h iAUC revealed a significant condition effect (P = 0.02) when collapsed across all 2-h time intervals but no significant difference between intervals (Fig. 2B).
Discussion
Chronically elevated glucose concentrations, and a subsequent increase in insulin secretion are characteristic of the progression towards type 2 diabetes. Increased levels of physical activity and exercise are recommended to help with glycemic control by improving insulin resistance. No prior studies have compared intermittent bouts of exercise with a continuous bout of exercise in controlling the glycemic excursions and insulin secretion over the course of 12-h, and while meals are being
Author contributions
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Holmstrup: design and conduct of the study, data collection and analysis, data interpretation and manuscript writing.
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Keslacy: conduct of the study, data interpretation and manuscript writing.
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Fairchild: design of the study, data analysis, data interpretation and manuscript writing.
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Weinstock: data interpretation and manuscript writing.
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Kanaley: design and conduct of the study, data collection and analysis, data interpretation and manuscript writing.
Conflict of interest
There is nothing to disclose for any of the authors.
Acknowledgments
We thank the individuals who participated in this study. This study was supported by an NIH R21DK084467-01 grant. There were no conflicts of interest for any of the authors of this manuscript.
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