Divergent serum metabolomic, skeletal muscle signalling, transcriptomic and performance adaptations to fasted versus whey protein-fed sprint interval training.

Sprint interval training (SIT) is a time efficient alternative to endurance exercise, conferring beneficial skeletal muscle metabolic adaptations. Current literature has investigated the nutritional regulation of acute and chronic exercise-induced metabolic adaptations in muscle following endurance exercise, principally comparing the impact of training in fasted and carbohydrate-fed (CHO) conditions. Alternative strategies such as exercising in low CHO, protein-fed conditions remain poorly characterised, specifically pertaining to adaptations associated with SIT. Thus, this study aimed to compare the metabolic and performance adaptations to acute and short term SIT in the fasted state with pre-exercise hydrolysed (WPH) or concentrate (WPC) whey protein supplementation. In healthy males, pre-exercise protein ingestion did not alter exercise-induced increases in PGC-1α, PDK4, SIRT1, and PPAR-δ mRNA expression following acute SIT. However, supplementation of WPC and WPH beneficially altered acute exercise-induced SIRT4 and CD36 mRNA expression, respectively. Pre-exercise protein ingestion attenuated acute exercise-induced increases in muscle pan-acetylation, and PARP1 protein content compared with fasted SIT. Acute serum metabolomic differences confirmed greater pre-exercise amino acid delivery in protein-fed compared with fasted conditions. Following 3 weeks of SIT, training-induced increases in mitochondrial enzymatic activity and exercise performance were similar across nutritional groups. Interestingly, resting muscle acetylation status was favourably regulated in WPH conditions following training. Such findings suggest pre-exercise WPC and WPH ingestion positively influences metabolic adaptations to SIT compared to fasted training, resulting in either similar or enhanced performance adaptations. Future studies investigating nutritional modulation of metabolic adaptations to exercise are warranted to build upon these novel findings.