Effect of Pre- and Intra-Exercise Nutritional Interventions on the Skeletal Muscle Metabolic and Functional Response to Endurance Exercise and Training

Abstract

This thesis presents studies investigating the impact of nutritional interventions on endurance exercise performance, and in modulating the adaptive response to endurance exercise training. The most efficacious time for pre-exercise caffeine ingestion remains uncertain, thus the role of timing of a caffeinated supplement on performance was investigated. Cyclists completed four experimental visits consisting of 30 minutes of cycling followed by a 15-minute time-trial. On three visits participants consumed caffeine either 35 minutes before cycling (PRE), at the onset of cycling (ONS), or immediately before the time-trial (DUR), with participants also completing a placebo condition (PLA). Cyclists completed 5% more work in in PRE than PLA, with no differences between any other trials, thus it appears caffeine ingestion approximately 70 minutes prior to a time-trial is optimal. Subsequently, I investigated if the tonicity of carbohydrate-electrolyte solutions influences their absorption rates or cycling performance. Cyclists performed 90 minutes of cycling without fluid consumption (DEH) or consuming hypotonic (HYPO), isotonic (ISO) or water drinks (H2O), followed by a 15-min time-trial. DEH decreased TT performance by 6.2% compared to H2O. There were no differences in the absorption rates or TT performance between drink conditions. Time-trial performance was similar following the ingestion of hypotonic, isotonic and water solutions, with the osmolality having no effect on the rate of fluid absorption. The final study of this thesis investigated whether β-alanine supplementation augments muscle carnosine content or the skeletal-muscle adaptations and performance improvements that may occur as a result of a period of high-intensity interval training. Participants consumed β-alanine or a placebo supplement for 12 weeks. Cycling capacity tests (CCT110) were performed at baseline (PRE-SUP), pre-training (POST-SUP) and post-training (POST-TRAIN). β-alanine supplementation had no effect on muscle carnosine concentrations POST-SUP however, they were elevated POST-TRAIN. CCT110 did not change from PRE-SUP to POST-SUP. Although performance improved following 8 weeks of training, β-alanine supplementation provided no enhancement.