Detrimental Effects Of Inactivity On Insulin Action

Abstract

A reduction in standing and ambulation (physical inactivity) lowers insulin action. Energy surplus also reduces insulin action, which mimics the effects of inactivity. Therefore, unless energy intake is reduced to match expenditure, a concurrent energy surplus may, at least partly, be responsible for the lower insulin action. PURPOSE: To evaluate the effect of inactivity with and without energy surplus on insulin action. METHODS: Twelve young (26.7 ± 4.4 years), lean (22.5 ± 6.6% fat), fit (VO2peak= 48.8 ± 3.4 ml·kg-1·min-1) men (n=7) and women (n=5) completed each of 3, 24-hour conditions: 1) high energy expenditure (e.g. standing, ambulating) in energy balance= LOW-SIT BAL; 2) low energy expenditure (sitting) with no change to energy intake (i.e. surplus)= HIGH-SIT SUR; 3) sitting with energy intake reduced to match low expenditure= HIGH-SIT BAL. Insulin action was measured during a glucose infusion the following morning,12 hours after a standardized meal. Data were analyzed by means of linear mixed-effects models using planned contrasts for post hoc comparisons. RESULTS: Steady-state plasma insulin (SSPI) was higher in HIGH-SIT SUR (42.7 ± 2.0 μU/mL) compared to HIGH-SIT BAL (36.2 ± 2.4 μU/mL; p = 0.07) and LOW-SIT BAL (30.8 ± 1.4 μU/mL; p < 0.05). Steady-state plasma glucose (SSPG) concentrations were similar between conditions (p > 0.05) Insulin action, estimated from SSPG · SSPI, was significantly lower in HIGH-SIT SUR compared to both HIGH-SIT BAL and LOW-SIT BAL (p < 0.05). Insulin action was also 14% lower in HIGH-SIT BAL compared to LOW-SIT BAL, although this difference was not statistically significant (p > 0.05). CONCLUSION: The detrimental effect of inactivity on insulin action is magnified if energy intake is not reduced to match low energy expenditure. Analysis of glucose kinetics will determine effects on hepatic glucose output and glucose disposal. Supported by an American College of Sports Medicine Foundation Research Grant.