Post‐exercise carbohydrate and energy availability induce independent effects on skeletal muscle cell signalling and bone turnover: implications for training adaptation

We examined the effects of post-exercise carbohydrate (CHO) and energy availability (EA) on potent skeletal muscle cell signalling pathways (regulating mitochondrial biogenesis and lipid metabolism) and indicators of bone metabolism. In a repeated measures design, nine males completed a morning (AM) and afternoon (PM) high-intensity interval (HIT) (8 x 5-min at 85% VO2peak) running protocol (interspersed by 3.5 hours) under dietary conditions of 1) high CHO availability (HCHO: CHO ~12 g.kg-1 , EA~ 60 kcal.kg-1 FFM), 2) reduced CHO but high fat availability (LCHF: CHO ~3 g.kg-1 , EA~ 60 kcal.kg-1 FFM) or 3), reduced CHO and reduced energy availability (LCAL: CHO ~3 g.kg-1 , EA~ 20 kcal.kg-1 FFM). Muscle glycogen was reduced to ~200 mmol.kg-1 dw in all trials immediately post PM-HIT (P<0.01) and remained lower at 17-h (171, 194 and 316 mmol.kg-1 dw) post PM-HIT in LCHF and LCAL (P<0.001) compared to HCHO. Exercise induced comparable p38MAPK phosphorylation (P<0.05) immediately-post PM-HIT and similar mRNA expression (all P<0.05) of PGC-1α, p53 and CPT1 mRNA in HCHO, LCHF and LCAL. Post-exercise circulating βCTX was lower in HCHO (P<0.05) compared to LCHF and LCAL, whereas exercise-induced increases in IL-6 were larger in LCAL (P<0.05) compared to LCHF and HCHO. In conditions where glycogen concentration is maintained within 200-350 mmol.kg-1 dw, we conclude post-exercise CHO and energy restriction (i.e.