How blood glucose responds to exercise depends on the timing of the physical activity with respect to the proximate meal. Although study after study has confirmed this, many researchers still report results without specifying exercise timing. This laxity could be the source of some of the uncertainties and inconsistencies found in the field. In place of the current practice of using the binary categorization of the feeding cycle into pre-meal and post-meal periods, we look at it as consisting of four time intervals: the pre-meal period plus the early, mid- and late postprandial periods. Two of these intervals stand out. Pre-meal exercise uses endogenous glucose and muscle glycogen as the main fuels offering varying effects on glycemia. Exercise during the mid-postprandial period uses exogenous glucose as the main fuel. Exogenous glucose is abundant in the blood during the 30 to 90 min post-meal period, rendering this interval a unique opportunity to use up the excess glucose as fuel for moderate aerobic exercise, thereby blunting the glucose surge. Hypoglycemia risk is minimal during this exercise window. The continuing arrival of glucose from the gut in copious amounts minimizes the risk for hypoglycemia. The role of different modes of exercise and combinations during the mid-postprandial period on metabolic markers remains to be explored.
- exercise timing
- pre-meal exercise
- post-meal exercise
- exercise window
- Copyright © 2016, Journal of Applied Physiology