Abstract
Objectively measured physical activity (PA) intensity has traditionally been categorized as light, moderate, and vigorous using laboratory calibrated cut points. The relative contribution of time spent across a spectrum of accelerometer-determined intensities on health outcomes is less clear. This study aimed to assess the relationship between objectively measured PA intensity on a continuous scale and markers of insulin sensitivity (IS). Participants at high risk of type 2 diabetes mellitus were recruited from primary care (Leicestershire, UK). PA was measured using an ActiGraph accelerometer. Fasting and postchallenge glucose and insulin levels were assessed using an oral glucose tolerance test. IS was calculated using the Matsuda-IS and the HOMA-IS indices. Log-linear regression modeling was used to assess the relationship between PA intensity, in increments of 500 counts per minute, with markers of IS. Models were controlled for known confounders. Complete data were available for 569 participants. PA intensity was favorably associated with fasting and 2 h of insulin and IS, with the association increasing in magnitude with each increment of 500 counts per minute. Differences in HOMA-IS per 10 min of PA ranged from 12.4% (95% confidence interval = 3.7%-21.8%) to 26.8% (11.0%-44.7%) within the moderate-intensity PA category (from 2000-2499 to 3500-3999 counts per minute). For Matsuda-IS, these differences were 22.0% (10.3%-34.9%) and 34.7% (13.9%-59.3%), respectively. Significant associations for fasting insulin were no longer observed after controlling for body mass index, whereas differences associated with 2-h insulin and IS were attenuated but still significant. PA of any intensity may positively influence glucose regulation and insulin sensitivity in individuals at high risk of type 2 diabetes mellitus in a dose-response manner. Further research is required to identify the intensity thresholds at which clinically relevant benefits occur in this population.
Highlights
The increasing prevalence and associated social and economic burden of type 2 diabetes (T2DM) is widely acknowledged.[43]
Physical activity is a powerful therapeutic agent in the promotion of insulin sensitivity [6] and favourable blood plasma glucose levels.[7]. Evidence ranging from epidemiological data to randomised control trials consistently demonstrate strong associations of moderate to vigorous physical activity (MVPA) with cardiovascular health and glycaemic control in individuals with T2DM.[2, 7] The globally accepted recommendation that all adults should engage in 150 minutes of moderate-intensity PA (MPA) or 75 minutes of vigorous-intensity PA (VPA) per week is encouraged in people with and at high risk of T2DM.[8]
Sensitivity Analyses Subgroup analysis revealed that there were no differences in any of the outcomes when the data were stratified by IGR status, except for the relationship between PA intensities between 500-999cpm and fasting glucose (p=0.037). This analysis indicated that the relationship between PA and fasting glucose was stronger in those with IGR with fasting glucose levels 0.7% (0.1, 1.2%) lower per 10mins of PA than those with normal glucose tolerance; 0.1% (0.0, 0.3%) There were no sex or age by intensity interactions. In this cohort of individuals identified as being at high risk of IGR or with undiagnosed T2DM, time spent in 500 cpm increments in objectively assessed PA intensity were linearly associated with lower levels of fasting and 2 hour insulin and 2 hour glucose and higher scores of indexes of insulin sensitivity
Summary
The increasing prevalence and associated social and economic burden of type 2 diabetes (T2DM) is widely acknowledged.[43]. Accelerometer measured PA intensity has generally been presented using population dependent counts-per-epoch cut-points categorised as sedentary, light, moderate or vigorous physical activity, with MPA and VPA usually combined and analysed as MVPA. These cut-points have been caibrated against energy expenditure, confirming their “constuct validity”, but the “external validity” such as the doseresponse relationship between incremental accelerometer measured PA intensity in counts per minute and health outcomes has been less rigorously tested. The aim of this study was to determine the association of time spent in objectively assessed incremental PA intensities with markers of insulin sensitivity; a precursor to T2DM, in free-living environments in individuals at high risk of T2DM. Purpose To assess the relationship between objectively measured PA intensity on a continuous scale and markers of insulin sensitivity
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