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Pronounced limb and fibre type differences in subcellular lipid droplet content and distribution in elite skiers before and after exhaustive exercise

Although lipid droplets in skeletal muscle are an important energy source during endurance exercise, our understanding of lipid metabolism in this context remains incomplete. Using transmission electron microscopy, two distinct subcellular pools of lipid droplets can be observed in skeletal muscle – one beneath the sarcolemma and the other between myofibrils. At rest, well‐trained leg muscles of cross‐country skiers contain 4‐ to 6‐fold more lipid droplets than equally well‐trained arm muscles, with a 3‐fold higher content in type 1 than in type 2 fibres. During exhaustive exercise, lipid droplets between the myofibrils but not those beneath the sarcolemma are utilised by both type 1 and 2 fibres. These findings provide insight into compartmentalisation of lipid metabolism within skeletal muscle fibres.