This study compared two high carbohydrate (CHO) diets in 14 male runners for effects on muscle glycogen deposition, endurance, and sensations of gastrointestinal discomfort. Muscle glycogen was measured in the vastus lateralis at rest and run time to exhaustion at 75 % VO2max was measured following 3-1/2 days on a 50% CHO diet. After 14 days the subjects consumed a 20% CHO diet and continued training to reduce glycogen. During the next 3-1/2 days, subjects ran less and consumed a 90% CHO diet emphasizing pasta and rice (Pasta, n=7) or lesser amounts of pasta and rice supplemented by a maltodextrin beverage (Supplement, n=7). Glycogen was again measured, followed by a second run to exhaustion. Compared to the 50% CHO diet, Pasta increased muscle glycogen by 27.1 ± 12.2 mmoles/kg muscle (M±SE; p < 0.05) and run time by 15.7±5.9 min; Supplement increased glycogen by 43.2 ± 13.5 mmoles/kg (p < 0.05) and run time by 29.0 ± 7.4 min (p < 0.05). Total glycogen concentrations and run times were not significantly different for Pasta versus Supplement. Subjects reported less gastrointestinal discomfort and greater overall preference for Supplement than for Pasta. Thus, glycogen loading can be accomplished at least as effectively and more comfortably by substituting a maltodextrin drink for some of the pasta and rice in a glycogen loading diet.
David R. Lamb, Ann C. Snyder and Thomas S. Baur
Hedy C. Reynolds, Loren Cordain, Mary A. Harris and Sheri Linnell
Thirteen trained runners were studied to determine whether postexercise glucose ingestion contributes to electrocardiogram (ECG) alterations by enhancing decreases in serum potassium (K+) concentrations. For the two randomly ordered trials, subjects ingested a 100 g (25% w/v glucose polymer) drink, either alone or with the addition of 3 g of potassium chloride (KCI), within 15 min following a 90-min run. ECG parameters, serum
José Moncada-Jiménez, Eric P. Plaisance, Michael L. Mestek, Lance Ratcliff, Felipe Araya-Ramírez, James K. Taylor, Peter W. Grandjean and Luis F. AragónVargas
This study investigated the effects of short-term dietary changes on metabolism and duathlon performance.
Eleven men underwent a high-fat (HF; >65% fat from energy) or a high-carbohydrate (CHO; HC) diet (>60% CHO from energy). Energy intake was individualized, and commercially available foods were prepared and packaged for each participant 48 hr before they completed a laboratory-based duathlon (5-km run, 30 km cycling, and 10-km run). Blood samples were obtained before, immediately after, and 1 and 2 hr after the duathlon for determination of glucose, insulin, and glucagon. Oxygen consumption, ratings of perceived exertion (RPE), and respiratory-exchange ratio were assessed, and fat and CHO oxidation were estimated before, during, and after the duathlon.
Dietary records indicated a significant difference in fat content ingested before the duathlons (p < .05). Time to complete the duathlon did not differ between the HC- and the HF-diet trials. CHO-oxidation rate was higher during the HC-diet trial than during the HF-diet trial (p = .006). Fat-oxidation rates were higher in the HF-diet trial than in the HC-diet trial (p = .001). No differences in RPE were found between dietary trials. Blood glucose concentration was higher immediately after the duathlon in the HC-diet trial than in the HF-diet trial and remained higher 1 and 2 hr after the duathlon (p < .05).
Duathlon performance was not altered by short-term changes in dietary fat or CHO composition despite higher blood glucose concentrations under the HC condition.
Ann C. Grandjean
A three-part questionnaire was used to identify professionals in sports nutrition and survey their recommendations on various aspects of sports nutrition. The majority of respondents were women. Over half of the sample reported working in sports nutrition for 6 years or less, and 72% indicated that 40% or less of their job is dedicated to sports nutrition. A portion of the questionnaire assessed the subjects' opinions on various sports nutrition topics. Statements on water and electrolytes generated the most agreement while statements on protein generated the least agreement. There was a positive correlation (p~0.004) between level of education and whether or not the respondents recommended glycogen loading, and a positive correlation (p~0.008) between the subjects' use of dietary supplements and the fact that they recommended supplements to the athletes they counseled. The majority of professionals in this study worked with recreational athletes and were more concerned about encouraging a healthy diet than improving athletic performance.
Christopher C. Webster, Jeroen Swart, Timothy D. Noakes and James A. Smith
during training. Finally, the potential benefits of other dietary strategies, such as glycogen loading, require investigation. Limitations The findings from this case study should be interpreted with caution as they are based on the performances of a single athlete using an n = 1 experimental protocol
Alan J. McCubbin, Anyi Zhu, Stephanie K. Gaskell and Ricardo J.S. Costa
issues in using such techniques on oxidation rate accuracy, including measures taken to deplete 13 C glycogen stores prior to 13 C-free glycogen reloading, and prolonged dietary control of 13 C-free foods to ascertain a 13 C-free glycogen load prior to the experimental protocol, both of which have
Joseph J. Matthews, Edward N. Stanhope, Mark S. Godwin, Matthew E.J. Holmes and Guilherme G. Artioli
-low carbohydrate diet ( Kreitzman et al., 1992 ) and evidence that glycogen loading from a depleted state increases body mass by ∼3.4% ( Bone et al., 2017 ). The latter changes may reflect the changes in MMA, where athletes typically utilize a low-carbohydrate diet during RWL and have high-carbohydrate intakes
Trent Stellingwerff, Ingvill Måkestad Bovim and Jamie Whitfield
.2003.045872 Martin , D.E. , & Coe , P.N. ( 1991 ). Training distance runners . Champaign, IL : Leisure Press . Maughan , R.J. , & Poole , D.C. ( 1981 ). The effects of a glycogen-loading regimen on the capacity to perform anaerobic exercise . European Journal of Applied Physiology and
Claire E. Badenhorst, Katherine E. Black and Wendy J. O’Brien
hepcidin were sustained 3-hr postexercise. Postexercise IL-6 levels were also attenuated under the high-CHO diet compared with a low-CHO condition ( Badenhorst et al., 2015a ). Previously, nutritional practices for endurance athletes have focused on glycogen-loading protocols to enhance athletic
Louise M. Burke, John A. Hawley, Asker Jeukendrup, James P. Morton, Trent Stellingwerff and Ronald J. Maughan
strategy • First glycogen loading protocol, developed serendipitously from studies of training/diet manipulation in the 1960s to achieve an increase in muscle fuel stores in preparation for a lengthy sporting event in which these stores would otherwise be limiting for performance. • Original models