Intramyocellular triacylglycerol in prolonged cycling with high- and low-carbohydrate availability

Vastus lateralis intramyocellular lipid (IMCL) content was assessed by (1)H-magnetic resonance spectroscopy before and after prolonged time trial cycling bouts of approximately 3-h duration. Six highly trained male cyclists completed a double-blind, randomized, crossover design of two experimental trials after a strenuous exercise bout and 48 h of high (HC) (9.32 +/- 0.08 g. kg(-1). day(-1)) and low (LC) (0.59 +/- 0.21 g. kg(-1). day(-1)) dietary carbohydrate. Resting IMCL content was significantly higher after LC vs. HC (P < 0.01) and was reduced during exercise by 64 and 57%, respectively. IMCL was not different between conditions after exercise (P > 0.05). The approximately twofold increase in IMCL degradation in LC compared with HC suggests that higher rates of whole body lipid metabolism in LC were in part attributable to a greater IMCL utilization. Four subjects experienced reductions of IMCL in excess of 70% during exercise. To our knowledge, this is the first study to report near depletion of IMCL during prolonged cycling, indicating that IMCL, presumably the triacylglycerol component, may be exhausted by prolonged strenuous exercise.