High intensity interval training (HIIT) has recently emerged as a time efficient alternative to conventional endurance exercise, conferring similar or superior benefits in terms of metabolic and performance adaptations in both athletic and non-athletic populations. Some of these physiological adaptations include augmented mitochondrial biogenesis and improved substrate metabolism in peripheral tissues such as skeletal muscle. However, nutritional strategies to optimise the adaptations to HIIT have yet to be established. Recent evidence suggests that acute nutritional status can affect the molecular regulation of genes mediating substrate metabolism and mitochondrial biogenesis. Moreover, preliminary evidence suggests that completion of exercise in fasted conditions augments some of these exercise-induced adaptations compared with the fed state. Given the fact that the transient molecular adaptations to acute exercise mediate long-term physiological adaptations, an investigation into the effects of different nutritional interventions on metabolic and performance responses to HIIT is warranted.

The purpose of this study is to determine the effects of fasted vs. fed-state (Whey Protein) HIIT on metabolic and performance adaptations in the acute (single exercise session) and chronic (3 weeks, 9 exercise sessions) phases. The primary hypothesis is that different pre-exercise feeding conditions (e.g. fasted placebo vs. Whey protein fed) will result in divergent physiological adaptations in terms of skeletal muscle metabolism and performance, both in response to a single HIIT session and a chronic HIIT intervention.

High intensity interval training (HIIT) has recently emerged as a time efficient alternative to conventional endurance exercise, conferring similar or superior benefits in terms of metabolic and performance adaptations in both athletic and non-athletic populations. Some of these physiological adaptations include augmented mitochondrial biogenesis and improved substrate metabolism in peripheral tissues such as skeletal muscle. However, nutritional strategies to optimise the adaptations to HIIT have yet to be established. Recent evidence suggests that acute nutritional status can affect the molecular regulation of genes mediating substrate metabolism and mitochondrial biogenesis. Moreover, preliminary evidence suggests that completion of exercise in fasted conditions augments some of these exercise-induced adaptations compared with the fed state. Given the fact that the transient molecular adaptations to acute exercise mediate long-term physiological adaptations, an investigation into the effects of different nutritional interventions on metabolic and performance responses to HIIT is warranted.

The purpose of this study is to determine the effects of fasted vs. fed-state (Whey Protein) HIIT on metabolic and performance adaptations in the acute (single exercise session) and chronic (3 weeks, 9 exercise sessions) phases. The primary hypothesis is that different pre-exercise feeding conditions (e.g. fasted vs. Whey protein fed) will result in divergent physiological adaptations in terms of skeletal muscle metabolism and performance, both in response to a single HIIT session and a chronic HIIT intervention.

A randomly assigned, parallel group, simple pre-post design has been adopted to answer this question. 3 groups of young (aged 18-35 y), healthy, recreationally active, aerobically untrained (VO2max <50 ml.kg.min-1), protein sufficient (>0.8 g.kg.d-1), males will undertake 3 weeks (9 sessions) of HIIT under different nutrient conditions following >10h overnight fast: i) Fasted placebo (0.33g.kg-1 body mass artificially flavoured and textured placebo); ii) Fed Whey protein (0.33g.kg-1 body mass intact whey protein 45 minutes prior to exercise); iii) Fed Whey protein hydrolysate (0.33g.kg-1 body mass hydrolysed whey protein 45 minutes prior to exercise). Participants will undergo biological sampling (venous blood and muscle biopsy) and measures of performance pre and post the intervention.

Inclusion Criteria:

• Healthy (absence of clinical condition)
• Recreationally active
• Aerobically untrained (VO2max <50 ml.kg.min-1)
• Protein sufficient (>0.8 g.kg.d-1)
• Males
• Able to provide informed consent
• No contraindications to high intensity exercise

Exclusion Criteria:

• BMI >30 kg.m-2
• Metabolic disease (mitochondrial, Type 2 Diabetes)

Participants are block randomised to one of three nutrient conditions on provision of informed consent. This information is held by the PI and members of the research team independent of the outcomes assessor (masked). All three beverages are made up by members of the research team independent of the outcomes assessor (masked) and the participants (masked). Each participant (masked) is provided with a drink in a black, non-transparent, container with no details of its contents other than that is a "nutrient supplement".