Relationship Of Skeletal Muscle Oxidative Capacity With Intramyocellular And Extramyocellular Lipids In Young And Older Individuals

The skeletal muscle contains lipids inside and outside of the cells, which are referred as intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL), respectively. Excessive accumulation of EMCL has been confirmed in older individuals and leads metabolic disorder and decline of muscle strength. On the other hand, IMCL becomes an important substrate for energy production. Muscle oxidative capacity had a potential to determine muscle lipid metabolism; therefore, it speculated that muscle oxidative capacity was related to muscle lipid accumulations. PURPOSE: The purpose of this study was to investigate whether muscle oxidative capacity is related with IMCL and EMCL in young and older individuals. METHODS: Eighteen young and fourteen older individuals participated in this study. Muscle oxidative capacity was assessed by the recovery rate of muscle oxygen saturation after the exercise and repeated arterial occlusions by near-infrared spectroscopy from medial gastrocnemius (MG). IMCL and EMCL were assessed by magnetic resonance spectroscopy from MG. RESULTS: A relationship between muscle oxidative capacity and IMCL was confirmed in young (r = -0.47, P < 0.05), but not in older individuals (r = 0.22, P = 0.45). Muscle oxidative capacity did not show significant relationships with EMCL both in young (r = 0.08, P = 0.77) and older individuals (r = 0.04, P = 0.89). CONCLUSIONS: We identified that IMCL in young individuals had a potential to contribute muscle lipid metabolism, which may indicate the capacity of muscle energy production into mitochondria.