Two weeks of single-leg immobilization alters intramyocellular lipid storage characteristics in healthy, young women

Muscle disuse rapidly induces insulin resistance (IR). Despite a relationship between intramyocellular lipid (IMCL) content and IR, during muscle-disuse IR develops before IMCL accumulation, suggesting that IMCL are not related to disuse-induced IR. However, recent studies show that it is not total IMCL, but IMCL size and location that are related to IR. Changes in these IMCL parameters may occur prior to increases in IMCL content, thus contributing to disuse-induced IR. Omega-3 fatty acids may mitigate the effects of disuse on IR by preventing a decline in insulin signaling proteins. Twenty women (age 22±3 y) received either 5g·d-1 omega-3 fatty acid or isoenergetic sunflower oil for 4-weeks prior to, throughout 2-weeks of single-leg immobilization, and during 2-weeks of recovery. Changes in IMCL characteristics and insulin signaling proteins were examined in vastus lateralis samples taken prior to supplementation and immobilization, and following immobilization and recovery. Omega-3 supplementation had no effect. IMCL area density decreased in the subsarcolemmal region during immobilization and recovery (-19% and -56%, respectively, p=0.009). IMCL size increased in the central intermyofibrillar region during immobilization (43%, p=0.007), returning to baseline during recovery. PLIN5 and AKT increased during immobilization (87%, p=0.002; 30%, p=0.007, respectively). PLIN 5 remained elevated and AKT increased further (15%) during recovery. IRS1, AS160 and GLUT4 decreased during immobilization (-35%, p=0.001; -44%, p=0.03; -56%, p=0.02, respectively), returning to baseline during recovery. Immobilization alters IMCL storage characteristics while negatively affecting unstimulated insulin signaling protein content in young women.