Quadriceps muscles were harvested from male CrATfl/fl and CrATSM−/− littermates at rest or 10 min and 1 h after 12 min of high intensity exercise. Tandem mass spectrometry was used to measure muscle concentrations of (A) acetylcarnitine, (B) acetyl-CoA and (C) the ratio of acetylcarnitine:acetyl-CoA. The same muscles were used to measure (D) phosphocreatine (PCr), (E) glycogen, and (F) exercise-induced glycogen breakdown, calculated as the difference between pre and post exercise. (G) Quantified plantaris muscle fiber type composition data (triplicate sections counted). (H) Representative fiber type images from plantaris; blue (type 1), red (2a), green (2b), unstained (2x). Data are means ± SEM, n=4–8 per group. ^Exercise effect, * Genotype effect (p<0.05).