Endocrine Abstracts

Introduction: Ectopic lipids are fuel stores in non-adipose tissues (i.e. skeletal muscle (IMCL), liver (IHCL), heart (ICCL)). An aerobic-exercise bout leads to a decrease in IMCL (‘working tissues’), whereas it is not established whether a single but of exercise influences IHCL or ICCL.

Increased IMCL and IHCL have been related to impaired insulin action in skeletal muscle and liver. It is hypothesized that fat availability (subcutaneous and visceral fat mass), exercise capacity (VO_2max) and insulin sensitivity influences the exercise-induced changes in ectopic lipids.

Methods: 10 male, physically active subjects (age: 28.9±6.4 years; VO_2max: 56.3±6.4 ml/kg per min, BMI: 22.75±1.4 kg/m²) were recruited. VO_2max was assessed using spiroergometry, insulin sensitivity by HOMA-index. Visceral and subcutaneous fat mass were separately quantified by MRI. IMCL, IHCL and ICCL were measured using ¹H-MR-spectroscopy before and after a 2 h-exercise at 50–60% of VO_2max. In a subgroup of five subjects, a third ectopic lipid assessment was performed a day after the 2 h-exercise test.

Results: A 2 h-exercise resulted in a significant decrease from baseline in IMCL (−17±22%, P=0.008), ICCL (−17±14%, P=0.002) and an increase in IHCL (42±29%, P=0.004). No significant correlations were found between the respective changes in ectopic lipids and measures of fat availability, exercise capacity or insulin sensitivity. MR-spectroscopy a day after exercise showed an re-increase of IMCL and ICCL still below pre-exercise values (IMCL: −3% (P=0.6), ICCL: −22% (P<0.05). In contrast, IHCL decreased to a level that was not significantly different to the pre-exercise level.

Conclusions: i) In healthy subjects all ectopic lipids are flexible fuel stores that are influenced by physical exercise, albeit in different directions with a decrease in myocardium and skeletal muscle (‘working tissues’) and an increase in liver (‘storage tissue’).

ii) Preliminary data suggest that this is a transitory phenomenon.