This study investigated the effect of initial muscle glycogen on performance of repeated sprints and some potential mechanisms for an effect of glycogen on fatigue. Eight subjects performed 2 cycling trials (repeated 60-s sprints) following consumption of either a high carbohydrate (HC) or a low carbohydrate (LC) diet. Muscle biopsies and blood samples were collected at baseline, following a 15% (15% fatigue) and a 30% decline in sprint performance (30% fatigue), when exercise was terminated. Baseline muscle glycogen levels [346 ± 19 HC (SEM) vs. 222 ± 19 mmol/kg dw LC] and total exercise time to 30% fatigue were higher following HC than LC (57.5 ± 10.0 vs. 42.0 ± 3.6 min; p < .05). Similar significant (p < .05) decreases over the entire exercise bout were seen in muscle glycogen (43%), creatine phosphate (CP; 35%), and sarcoplasmic reticu-lum (SR) Ca2+-uptake in isolated homogenized muscle (56%) for both trials (p > .05 between trials). The percentage decline in SR Ca2+-release was less for HC than LC (36% and 53%, respectively), but this was not statistically different. In summary, HC delayed fatigue during repeated sprints. As the reductions in muscle glycogen, CP, and SR function during exercise were not different by dietary treatment, these data do not support a link between whole muscle glyco-gen and SR function or CP reduction during repeated sprint exercise.
Michelle Smith Rockwell, Janet Walberg Rankin and Helen Dixon
Michelle Smith Rockwell, Sharon M. Nickols-Richardson and Forrest W. Thye
The purpose of this investigation was to assess nutrition knowledge, opinions, and practices of coaches and trainers at a Division I university. Participants (n = 53) completed questionnaires regarding nutrition knowledge, opinions, and practices. Descriptive statistics and analysis of variance were used to analyze data. Overall, participants responded correctly to 67% of nutrition knowledge questions. Participants who coached/trained female athletes tended to score better than respondents who coached/trained male athletes. Strength and conditioning coaches and participants with greater than 15 years of experience scored higher than other participants. Nutrition opinions/practices responses revealed that nutritional supplements were provided for all but 6% of participants’ athletes. Participants rated body weight as more important than body composition to athletes’ performances. Over 30% of participants perceived at least one case of disordered eating within the past year. Some participants (53%) felt that athletes may consume more nutritious meals on team-sponsored trips if given larger food allowances. Thirty percent of participants reported dietitians were available to them; the same percentage reported utilizing dietitians. Coaches and trainers are knowledgeable about some appropriate nutritional recommendations, but registered dietitians or qualified sports nutrition professionals may complement the nutrition-related education and counseling of athletes (23).
Michelle Smith, Hayley E. McEwan, David Tod and Amanda Martindale
The research team explored UK trainee sport and exercise psychologists’ perspectives on developing professional-judgment and decision-making (PJDM) expertise during their British Psychological Society Qualification in Sport and Exercise Psychology (Stage 2). An assorted analysis approach was adopted to combine an existing longitudinal qualitative data set with the collection and analysis of a new qualitative data set. Participants (1 female, 6 male) were interviewed 4 times over a 3-yr training period, at minimum yearly intervals. Interviews were transcribed verbatim and reflexive thematic analysis applied to transcripts using the theoretical concepts of PJDM. Experience, analytical reasoning, and observation of other practitioners’ practice was useful for developing PJDM expertise. PJDM expertise might be optimized through the use of knowledge-elicitation principles. For example, supervisors could embed critical cues in the anecdotes they share to expand the experience base that trainees can draw from when making decisions.
Louise M. Burke, Julie A Winter, David Cameron-Smith, Marc Enslen, Michelle Farnfield and Jacques Decombaz
The authors undertook 2 crossover-designed studies to characterize plasma amino acid (AA) responses to the intake of 20 g of protein. In Study 1, 15 untrained and overnight-fasted subjects consumed 20 g protein from skim milk, soy milk, beefsteak, boiled egg, and a liquid meal supplement. In Study 2, 10 fasted endurance-trained subjects consumed 20 g protein from a protein-rich sports bar at rest and after a 60-min submaximal ride. Plasma AA concentrations were measured immediately before and for 180 min after food ingestion using a gas-chromatography flame-ionization detection technique. A pharmacokinetic analysis was undertaken for profiles of total AAs (TAA), essential AAs, branched-chain AAs (BCAA), and leucine. Although area-under-the-curve values for plasma TAA were similar across protein sources, the pattern of aminoacidemia showed robust differences between foods, with liquid forms of protein achieving peak concentrations twice as quickly after ingestion as solid protein-rich foods (e.g., ~50 min vs ~100 min) and skim milk achieving a significantly faster peak leucine concentration than all other foods (~25 min). Completing exercise before ingesting protein sources did not cause statistically significant changes in the pattern of delivery of key AAs, BCAAs, and leucine apart from a 20–40% increase in the rate of elimination. These results may be useful to plan the type and timing of intake of protein-rich foods to maximize the protein synthetic response to various stimuli such as exercise.
Vandre C. Figueiredo, Michelle M. Farnfield, Megan L.R. Ross, Petra Gran, Shona L. Halson, Jonathan M. Peake, David Cameron-Smith and James F. Markworth
Purpose: To determine the acute effects of carbohydrate (CHO) ingestion following a bout of maximal eccentric resistance exercise on key anabolic kinases of mammalian target of rapamycin and extracellular signal-regulated kinase (ERK) pathways. The authors’ hypothesis was that the activation of anabolic signaling pathways known to be upregulated by resistance exercise would be further stimulated by the physiological hyperinsulinemia resulting from CHO supplementation. Methods: Ten resistance-trained men were randomized in a crossover, double-blind, placebo (PLA)-controlled manner to ingest either a noncaloric PLA or 3 g/kg of CHO beverage throughout recovery from resistance exercise. Muscle biopsies were collected at rest, immediately after a single bout of intense lower body resistance exercise, and after 3 hr of recovery. Results: CHO ingestion elevated plasma glucose and insulin concentrations throughout recovery compared with PLA ingestion. The ERK pathway (phosphorylation of ERK1/2 [Thr202/Tyr204], RSK [Ser380], and p70S6K [Thr421/Ser424]) was markedly activated immediately after resistance exercise, without any effect of CHO supplementation. The phosphorylation state of AKT (Thr308) was unchanged postexercise in the PLA trial and increased at 3 hr of recovery above resting with ingestion of CHO compared with PLA. Despite stimulating-marked phosphorylation of AKT, CHO ingestion did not enhance resistance exercise–induced phosphorylation of p70S6K (Thr389) and rpS6 (Ser235/236 and Ser240/244). Conclusion: CHO supplementation after resistance exercise and hyperinsulinemia does not influence the ERK pathway nor the mTORC1 target p70S6K and its downstream proteins, despite the increased AKT phosphorylation.