Effects of acute nutritional interventions on athletic performance
There have been few studies of the effects of nutritional strategies in training and competition settings in elite athletes. This thesis represents four studies that were performed to investigate the effect of specific acute supplementation protocols on performance and/or recovery from exercise. Studies 1-3 were experimental investigations of the recovery and/or performance effects of carbohydrate, carbohydrate-protein or caffeine supplements in elite swimmers. Study 4 was a meta-analytic review of the effects of acute carbohydrate supplementation on endurance performance. In Study 1, we have provided some evidence that consuming carbohydrate during and carbohydrate-protein immediately after a 2-h high-intensity swim session induces better recovery in plasma creatine kinase and salivary IgA compared with consuming water during exercise and carbohydrate-protein immediately after, and compared with consuming only carbohydrates during and immediately after exercise. These effects may indicate reduced muscle damage and better mucosal immunity in the upper respiratory tract. The inclusion of protein in the carbohydrate supplement also reduced inflammatory responses. As demonstrated in the meta-analysis (Study 4), consuming carbohydrate and carbohydrate-protein supplements during exercise can have large benefits in endurance performance: The best supplement inferred from the analysis consisted of the best regime derived from the analysis consisted of ingesting a ~3-10% carbohydrate-plus-protein drink providing ~0.7 g•kg-1•h-1 glucose polymers, ~0.2 g•kg-1•h-1 fructose and ~0.2 g•kg 1•h 1 protein in multiple boluses before and during exercise. Caution is required to extrapolate the results of the meta-analysis to short-duration exercise, because the meta-analysis included only one study with exercise duration <25 min. In Study 2, we found possible performance impairments in the last step of a 7x200-m step test (change in performance time 0.9%; 90% confidence limits ±1.1%) and in a 100-m time trial (0.1%; ±0.6%) with ingestion of a carbohydrate-protein supplement. In Study 3, we have provided some evidence that ingesting ~100 mg caffeine 75 min before training or competition time trials enhances performance in elite swimmers by ~1.3%. This intervention was part of a methodological investigation of a novel application of mixed linear modeling for monitoring athletic performance. Through this PhD research, we have demonstrated clear performance and recovery effects with specific acute supplementation protocols in elite swimmers. We have provided a novel approach to investigate effects of treatments in elite athletes, and we have demonstrated large effects with carbohydrate supplementation regimes in endurance exercise in an innovative meta-analytic review. We encourage athletes, sports scientists and coaches to estimate magnitudes of effects of treatments and individual responses to treatments using linear modeling of performance times.