An evidence-based approach to the application of the science of sports and exercise nutrition to optimising sporting performance

The primary objective of this series of experiments was to explore some of the reasons which lead to equivocal outcomes in the literature on dietary recommendations and to demonstrate the need for evidence-based data on well-trained and elite athletes. Therefore, the previous mentioned groups of athletes were recruited to participate in four research studies, each entailing a series of experimental trials. The data obtained were compared to previous research and/or to the established dietary recommendations. The aim of the first research study presented in this thesis (Chapter 2) was to examine the effects of Glycine-arginine-α-ketoisocaproic acid (GAKIC) supplementation on fatigue during high intensity, repeated cycle sprints in trained cyclists. It should be noted that despite the fact that studies on GAKIC supplementation involving well-trained subjects are lacking, athletes regularly use this commercially available supplement. This is is also the case for a vast range of other supplements whose suitability has been assessed in normal healthy subjects or recreationally active individuals. In the study presented in Chapter 2, 10 well-trained male cyclists completed two supra-maximal sprint tests each involving 10 sprints of 10 s separated by 50 s rest intervals on an electrically braked cycle ergometer. Participants ingested 11.2 g of GAKIC (according to protocols previously established in the literature) or Placebo (Pl) during a period of 45 min prior to the experimental trials. Peak power, mean power, fatigue index as well as heart rate (HR) and ratings of perceived exertion did not differ between conditions (GAKIC vs. Pl). Peak power declined from the 1st sprint (mean SD) (Pl: 1332 307 W, GAKIC: 1367 342 W) to the 10th sprint (Pl: 1091 229 W, GAKIC: 1061 272 W) and did not differ between conditions (P = 0.88). Mean power declined from the 1st sprint (Pl: 892 151 W, GAKIC: 892 153 W) to the 10th sprint (Pl: 766 120 W, GAKIC: 752 138 W) and did not differ between conditions (P = 0.96). Fatigue index remained at ~38% throughout the series of sprints and did not differ between conditions (P = 0.99). HR and ratings of perceived exertion increased from the 1st sprint to the 10th sprint and did not differ between conditions (P = 0.11 and P = 0.83, respectively). The data reported, suggest that GAKIC has no ergogenic effect on repeated bouts of high intensity exercise in trained individuals. The reported data further contradicts previous performance studies where GAKIC was found to attenuate the decline in power output, improve muscle performance and delay muscle fatigue resulting in the improvement of total work during high intensity exercise. Notably, none of the previous studies involving GAKIC supplementation seem to control for a number of possible confounding factors that could have adversely affected the results. For instance, utilization of untrained individuals and failure to include baseline trials to establish the repeatability of performance trials leaves the reliability of the data open to question. Furthermore, the results in Chapter 2 highlight the importance of extrapolating decisions concerning the effectiveness of a marketed nutritional supplement from the best available research conducted on well-trained subjects. The aim of Chapter 3 was to assess the food and macronutrient intake of elite Ethiopian distance runners; a group of athletes that dominates endurance running. The results of the research allowed further examination and direct comparison of the nutrient intake to the established guidelines and previous studies conducted on African runners. The dietary intake of 10 highly-trained Ethiopian long distance runners, living and training at high altitude was assessed during a 7-day period of intense training prior to competition using the standard weighed intake method. Training was also assessed using an activity/training diary. Body mass (BM) was stable (i.e., was well maintained) over the assessment period (pre: 56.7 ± 4.3 kg vs. post: 56.6 ± 4.2 kg, P = 0.54). The diet comprised of 13375 ± 1378 kJ and was high in carbohydrate (64.3 ± 2.6% of total energy intake (TEI), 545 ± 49 g, 9.7 ± 0.9 g.kg-1). Fat and protein intake was 23.3 ± 2.1% TEI (83 ± 14 g) and 12.4 ± 0.6% TEI (99 ± 13 g, 1.8 ± 0.2 g.kg-1), respectively. Fluid intake comprised mainly of water (1751 ± 583 mL.day-1), while no fluids were consumed before or during training with only modest amounts being consumed following training. It was concluded that, as found in previous studies on elite Kenyan distance runners, the diet of these elite Ethiopian distance runners met most recommendations for endurance athletes in regard to macronutrient intake but not in regard to fluid intake. Nevertheless, it remains unclear in what way these differences in fluid consumption, before major competitions, have an impact on their performance. Therefore, Chapter 3 highlights the fact that more studies involving truly world-class athletes are required in order to assess and possibly improve the applicability of current recommendations to elite athletes. Chapter 3 also highlights the potential role of the commercial industry in the application of the science of exercise nutrition. Chapter 4 aimed to describe the drinking behaviours of elite male marathon runners during major city marathons. Retrospective video analysis of 10 male marathon runners during 13 major city marathons was undertaken. Total drinking durations during the marathons were determined by estimating the time spent ingesting fluid at each drinking station from video images. The ambient conditions during the 13 studied marathon races were 15.3 ± 8.6 oC (ambient temperature) and 59 ± 17% relative humidity; average marathon competition time was 02:06:31 ± 00:01:08 (h:min:s). Total drinking duration during these races was 25.5 ± 15.0 s (range: 1.6 - 50.7 s) equating to an extrapolated fluid intake rate of 0.55 ± 0.34 L.h-1 (range: 0.03 - 1.09 L.h-1). No significant correlations were found between total drink duration, fluid intake (rate and total), running speed and ambient temperature. Estimated BM loss based on calculated sweat rates and rates of fluid ingestion was 8.8 ± 2.1% (range: 6.6 - 11.7%). Measurements of the winner in the 2009 Dubai marathon revealed a BM loss of -9.8%. It was concluded that the most successful runners during major city marathons, drink fluids ad libitum (i.e., at one's pleasure) for less than ~60 s at an extrapolated fluid ingestion rate and is in accordance with the current recommendations by the American College of Sports Medicine of 0.4 - 0.8 L.h-1. Nevertheless, these elite runners do not seem to maintain their BM within the current recommended ranges of 2 – 3%. On the other hand, this apparently widely adopted ad libitum strategy during marathon racing seems to produce optimal/winning performances. This evidence and the finding that the runner, who set the previous world record (2008), finished a competitive race (Dubai, 2009) with a BM loss of 9.8%, suggest that a tolerable range for dehydration may exist. It is possible, that this tolerable limit of dehydration may not have a negative impact on running performance in elite runners and may even confer an advantage by preventing a significant increase in BM due to “over - consumption” of large volumes of fluid. Given the data extrapolated from “real world” studies (Chapters 3 and 4) and the established guidelines for fluid ingestion, the investigation in Chapter 5 aimed to examine a possible method that could bring together the established guidelines and the data extracted from “real world” studies. Therefore, the effects of a hyper-hydration method combining creatine (Cr) and glycerol (Gly) supplementation on thermoregulatory responses and running economy (RE) in hot and cool conditions were investigated. Cr•H2O (11.4 g), Gly (1 g•kg-1 BM) and glucose polymer (75 g) were administered twice daily to 15 male endurance runners during a 7-day period. Exercise trials were conducted pre- and post-supplementation at 10 and 35 °C and 70% relative humidity. Combined Cr and Gly supplementation increased BM and total body water by 0.90 kg and 0.71 L, respectively following supplementation. Despite the significant increase in BM, supplementation had no effect on oxygen uptake (V̇O2) and thus RE. Both HR and core temperature were attenuated significantly after supplementation. Combining Cr and Gly is effective in reducing thermal and cardiovascular strain during exercise in the heat without negatively impacting RE. The potential influence of the commercial industry on scientific objectivity, as well as the lack of properly evaluated, controlled and randomized studies are the two main weaknesses that prevent the establishment of well accepted guidelines for food and fluid intake of well-trained and elite athletes. The development of novel guidelines needs to be solely evidence-based. Therefore, in order to reach conclusions regarding specific categories of athletes, research should be conducted on homogeneous groups (i.e., either well-trained, or elite, or world-class). Furthermore, research must be conducted under environmental and other conditions that are equivalent to those met during ‘‘outdoor’’ exercise, in order to evaluate and even improve the prevailing recommendations