Sex-based differences in IMCL storage and utilization during an acute bout of high intensity interval exercise (HIIE)

Abstract

INTRODUCTION: The contribution of lipids, particularly intramyocellular lipids (IMCL), to energy production during high intensity interval exercise (HIIE) is not well characterized. Sex influences lipid utilization during moderate intensity aerobic exercise and thus there may be differences in lipid utilization during HIIE as well. There is conflicting evidence as to whether there is a sex difference in IMCL utilization during exercise, which may be a result of improper matching, differences in methodology, or differential use in subcellular regions. PURPOSE: Our study aimed to determine whether IMCL are used during a bout of HIIE and whether sex influences the extent of IMCL utilization. We also examined whether sex or exercise influenced IMCL storage characteristics and morphology. METHODS: Young, healthy, recreationally active males (n=12) and females (n=12) were matched for aerobic fitness (mL O2• kgFFM-1) and performed an acute bout of HIIE (5 min warm up/cooldown @50W, 10 x 1-min @90% HRmax). Biopsies were collected from the vastus lateralis prior to and following exercise for electron microscopic determination of IMCL storage and western blot analysis of proteins related to lipid and aerobic metabolism RESULTS: Carbohydrate oxidation (p<0.0001) and the increase in blood lactate (p=0.02) were greater in males than females during HIIE, with no difference in fat oxidation (p=0.98). Sex had no effect on content of any proteins analyzed (all p>0.08) or on IMCL area density (all p>0.31). IMCL area density did not change during exercise (all p>0.37) and there was no difference in utilization between the sexes (all p>0.47).IMCL feret (p<0.001), perimeter (p<0.004)and average length of IMCL-mitochondria apposition (all p<0.03) were greater in males. IMCL number (p<0.03) and perimeter to area ratio (p<0.006) were greater in females. CONCLUSION: Fat and IMCL are not significant contributors to energy production during HIIE. Comparable rates of fat oxidation and a lesser increase in blood lactate in females suggest that females relied on anaerobic glycolysis to a lesser extent. Excitingly, our region-specific characterization of IMCL morphology establishes a basis for sex-difference investigation into IMCL storage characteristics.