Fig. 3.

A HFD increases mitochondrial capacity to oxidize fatty acids only in young mice. a Total PGC1α protein content in quadriceps homogenates normalized by glyceraldehyde 3-phosphate dehydrogenase (GAPDH) levels. b Citrate synthase activities measured in quadriceps homogenates and mitochondria-enriched suspensions.  Mitochondrial O₂ consumption fluxes were corrected for mitochondria enrichment of suspensions using the ratio between citrate synthase activity (CS) in the mitochondria vs in total homogenate (R = CS_mito/CS_homog). Maximal ADP-stimulated O₂ consumption per tissue protein is shown for palmitoyl-CoA and carnitine (c), pyruvate (d) and pyruvate and glutamate (e) as substrates, all in the presence of malate. Data are shown as mean ± SEM and were analysed using two-way ANOVA. Multiple comparisons were performed using Tukey’s correction, n = 4–6 (young groups) or 8–10 (old groups); **p < 0.01 (HFD vs LFD), *p < 0.05 (HFD vs LFD), matched ages. Supporting data values can be found in Additional file 10