Associations of physical activity intensities with markers of insulin sensitivity

BACKGROUND: Objectively measured physical activity (PA) intensity has traditionally been categorised 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. PURPOSE: To assess the relationship between objectively measured PA intensity on a continuous scale and markers of insulin sensitivity. METHODS: Participants at high risk of type 2 diabetes were recruited from primary care (Leicestershire, UK). PA was measured using an ActiGraph accelerometer. Fasting and post-challenge glucose and insulin levels were assessed using an oral glucose tolerance test. Insulin sensitivity (IS) was calculated using the Matsuda-IS and HOMA-IS indices. Log-linear regression modelling was used to assess the relationship between PA intensity, in 500 count per min (cpm) increments, with markers of IS. Models were controlled for known confounders. RESULTS: Complete data were available for 569 participants. PA intensity was favourably associated with fasting and 2 hour insulin and IS, with the association increasing in magnitude with each 500 cpm increment. Differences in HOMA-IS per 10 min of PA ranged from 12.4% (95% confidence intervals 3.7, 21.8%) to 26.8% (11.0, 44.7%) within the moderate-intensity PA category (from 2000-2499 cpm to 3500-3999 cpm). 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 BMI, whereas differences associated with 2 hour insulin and IS were attenuated but still significant. CONCLUSION: PA of any intensity may positively influence glucose regulation and insulin sensitivity in individuals at high risk of T2DM in a dose-response manner. Further research is required to identify the intensity thresholds at which clinically relevant benefits occur in this population.