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Dennis van Hamont, Christopher R. Harvey, Denis Massicotte, Russell Frew, François Peronnet and Nancy J. Rehrer

Effects of feeding glucose on substrate metabolism during cycling were studied. Trained (60.0 ± 1.9 mL · kg−1 · min−1) males (N = 5) completed two 75 min, 80% VO2max trials: 125 g 13C-glucose (CHO); 13C-glucose tracer, 10 g (C). During warm-up (30 min 30% VO2max) 2 ⋅ 2 g 13C-glucose was given as bicarbonate pool primer. Breath samples and blood glucose were analyzed for 13C/ 12C with IRMS. Protein oxidation was estimated from urine and sweat urea. Indirect calorimetry (protein corrected) and 13C/ 12C enrichment in expired CO2 and blood glucose allowed exogenous (Gexo), endogenous (Gendo), muscle (Gmuscle), and liver glucose oxidation calculations. During exercise (75 min) in CHO versus C (respectively): protein oxidation was lower (6.8 ± 2.7, 18.8 ± 5.9 g; P = 0.01); Gendo was reduced (71.2 ± 3.8, 80.7 ± 5.7%; P = 0.01); Gmuscle was reduced (55.3 ± 6.1, 65.9 ± 6.0%; P = 0.01) compensated by increased Gexo (58.3 ± 2.1, 3.87 ± 0.85 g; P = 0.000002). Glucose ingestion during exercise can spare endogenous protein and carbohydrate, in fed cyclists, without gly-cogen depletion.

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Kimberly Volterman, Daniel Moore, Joyce Obeid, Elizabeth A. Offord and Brian W. Timmons

Purpose:

In adults, rehydration after exercise in the heat can be enhanced with a protein-containing beverage; however, whether this applies to children remains unknown. This study examined the effect of milk protein intake on postexercise rehydration in children.

Method:

Fifteen children (10–12 years) performed three exercise trials in the heat (34.4 ± 0.2 °C, 47.9 ± 1.1% relative humidity). In a randomized, counterbalanced crossover design, participants consumed iso-caloric and electrolyte-matched beverages containing 0 g (CONT), 0.76 g (Lo-PRO) or 1.5 g (Hi-PRO) of milk protein/100 mL in a volume equal to 150% of their body mass (BM) loss during exercise. BM was then assessed over 4 h of recovery.

Results:

Fluid balance demonstrated a significant condition × time interaction (p = .012) throughout recovery; Hi-PRO was less negative than CONT at 2 hr (p = .01) and tended to be less negative at 3 h (p = .07). Compared with CONT, beverage retention was enhanced by Hi-PRO at 2 h (p < .05).

Conclusion:

A postexercise beverage containing milk protein can favorably affect fluid retention in children. Further research is needed to determine the optimal volume and composition of a rehydration beverage for complete restoration of fluid balance.

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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.

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Ricardo J.S. Costa, Beat Knechtle, Mark Tarnopolsky and Martin D. Hoffman

consumption of sufficient protein to meet daily nitrogen balance (i.e., 1.2–2.0 g·kg −1 ·day −1 ), to support tissue recovery and adaptations ( Phillips & van Loon, 2011 ; Tarnopolsky et al., 1988 ). Habitual dietary protein needs for elite endurance athletes are estimated to be 1.6–1.8 g·kg −1 ·day −1

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James A. Betts, Milou Beelen, Keith A. Stokes, Wim H.M. Saris and Luc J.C. van Loon

Nocturnal endocrine responses to exercise performed in the evening and the potential role of nutrition are poorly understood. To gain novel insight, 10 healthy men ingested carbohydrate with (C+P) and without (C) protein in a randomized order and double-blind manner during 2 hr of interval cycling followed by resistancetype exercise and into early postexercise recovery. Blood samples were obtained hourly throughout 9 hr of postexercise overnight recovery for analysis of key hormones. Muscle samples were taken from the vastus lateralis before and after exercise and then again the next morning (7 a.m.) to calculate mixed-muscle protein fractional synthetic rate (FSR). Overnight plasma hormone concentrations were converted into overall responses (expressed as area under the concentration curve) and did not differ between treatments for either growth hormone (1,464 ± 257 vs. 1,432 ± 164 pg/ml · 540 min) or total testosterone (18.3 ± 1.2 vs. 17.9 ± 1.2 nmol/L · 540 min, C and C+P, respectively). In contrast, the overnight cortisol response was higher with C+P (102 ± 11 nmol/L · 540 min) than with C (81 ± 8 nmol/L · 540 min; p = .02). Mixed-muscle FSR did not differ between C and C+P during overnight recovery (0.062% ± 0.006% and 0.062% ± 0.009%/hr, respectively) and correlated significantly with the plasma total testosterone response (r = .7, p < .01). No correlations with FSR were apparent for the response of growth hormone (r = –.2, p = .4), cortisol (r = .1, p = .6), or the ratio of testosterone to cortisol (r = .2, p = .5). In conclusion, protein ingestion during and shortly after exercise does not modulate the endocrine response or muscle protein synthesis during overnight recovery.

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Thomas B. Walker, Jessica Smith, Monica Herrera, Breck Lebegue, Andrea Pinchak and Joseph Fischer

The purpose of this study was to investigate the ability of whey-protein and leucine supplementation to enhance physical and cognitive performance and body composition. Thirty moderately fit participants completed a modified Air Force fitness test, a computer-based cognition test, and a dual-energy X-ray-absorptiometry scan for body composition before and after supplementing their daily diet for 8 wk with either 19.7 g of whey protein and 6.2 g leucine (WPL) or a calorie-equivalent placebo (P). Bench-press performance increased significantly from Week 1 to Week 8 in the WPL group, whereas the increase in the P group was not significant. Push-up performance increased significantly for WPL, and P showed a nonsignificant increase. Total mass, fat-free mass, and lean body mass all increased significantly in the WPL group but showed no change in the P group. No differences were observed within or between groups for crunches, chin-ups, 3-mile-run time, or cognition. The authors conclude that supplementing with whey protein and leucine may provide an advantage to people whose performance benefits from increased upper body strength and/or lean body mass.

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Paul W. Macdermid and Stephen R. Stannard

This study compared a training diet recommended for endurance athletes (H-CHO) with an isoenergetic high protein (whey supplemented), moderate carbohydrate (H-Pro) diet on endurance cycling performance. Over two separate 7-d periods subjects (n = 7) ingested either H-CHO (7.9 ± 1.9 g · kg−1 · d−1 carbohydrate; 1.2 ± 0.3 g · kg−1 · d−1 fat; 1.3 ± 0.4 g · kg−1 · d−1 protein) or H-Pro (4.9 ± 1.8 g · kg−1 · d−1; 1.2 ± 0.3 g · kg−1 · d−1; 3.3 ± 0.4 g · kg−1 · d−1) diet in a randomized, balanced order. On day 8 subjects cycled (self-paced) for a body weight dependent (60 kJ/bm) amount of work. No differences occurred between energy intake (P = 0.422) or fat intake (P = 0.390) during the two dietary conditions. Performance was significantly (P = 0.010) impaired following H-Pro (153 ± 36) compared with H-CHO (127 ± 34 min). No differences between treatments were observed for physiological measures taken during the performance trials. These results indicate an ergolytic effect of a 7-d high protein diet on self-paced endurance cycling performance.

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Marco Malaguti, Marta Baldini, Cristina Angeloni, Pierluigi Biagi and Silvana Hrelia

The authors evaluated the role of a high-protein, low-calorie, polyunsaturated fatty-acid (PUFA) -supplemented diet on anthropometric parameters, erythrocytemembrane fatty-acid composition, and plasma antioxidant defenses of nonprofessional volleyball athletes. The athletes were divided in two groups: One (n = 5) followed the Mediterranean diet, and the other (n = 6) followed a high-protein, low-calorie diet with a 3-g/day fish-oil supplementation. All the athletes had anthropometric measurements taken, both at the beginning and at the end of the study, which lasted for 2 months. Body-mass index and total body fat were significantly diminished in the second group, while they remained unchanged in the first. Plasma total antioxidant activity (TAA) was significantly increased in the plasma of both groups, with no differences between the groups, suggesting that physical activity, not the different diets, is the main contributor to the increase of plasma TAA. The second group showed a significant increase in erythrocytemembrane PUFA content and in the unsaturation index value (UI) because of the fish-oil supplementation. A high-protein, low-carbohydrate, fish-oil-supplemented diet seems to be useful only when the aim of the diet is to obtain weight loss in a short-term period. The significant increase in the UI of erythrocyte membranes indicates the potential for harm, because a high intake of PUFA might increase susceptibility to lipid peroxidation not counterbalanced by a higher increase in TAA. Adherence to the Mediterranean diet seems to be the better choice.

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James A. Betts, Keith A. Stokes, Rebecca J. Toone and Clyde Williams

Endocrine responses to repeated exercise have barely been investigated, and no data are available regarding the mediating influence of nutrition. On 3 occasions, participants ran for 90 min at 70% VO2max (R1) before a second exhaustive treadmill run at the same intensity (R2; 91.6 ± 17.9 min). During the intervening 4-hr recovery, participants ingested either 0.8 g sucrose · kg−1 · hr−1 with 0.3 g · kg−1 · hr−1 whey-protein isolate (CHO-PRO), 0.8 g sucrose · kg−1 · hr−1 (CHO), or 1.1 g sucrose · kg−1 · hr−1 (CHO-CHO). The latter 2 solutions therefore matched the former for carbohydrate or for available energy, respectively. Serum growth-hormone concentrations increased from 2 ± 1 μg/L to 17 ± 8 μg/L during R1 considered across all treatments (M ± SD; p ≤ .01). Concentrations were similar immediately after R2 irrespective of whether CHO or CHO-CHO was ingested (19 ± 4 μg/L and 19 ± 5 μg/L, respectively), whereas ingestion of CHO-PRO produced an augmented response (31 ± 4 μg/L; p ≤ .05). Growth-hormone-binding protein concentrations were unaffected by R1 but increased similarly across all treatments during R2 (from 414 ± 202 pmol/L to 577 ± 167 pmol/L; p ≤ .01), as was the case for plasma total testosterone (from 9.3 ± 3.3 nmol/L to 14.7 ± 4.6 nmol/L; p ≤ .01). There was an overall treatment effect for serum cortisol (p ≤ .05), with no specific differences at any given time point but lower concentrations immediately after R2 with CHO-PRO (608 ± 133 nmol/L) than with CHO (796 ± 278 nmol/L) or CHO-CHO (838 ± 134 nmol/L). Ingesting carbohydrate with added whey-protein isolate during short-term recovery from 90 min of treadmill running increases the growth-hormone response to a second exhaustive exercise bout of similar duration.

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Elizabeth M. Broad, Ronald J. Maughan and Stuart D.R Galloway

Twenty nonvegetarian active males were pair-matched and randomly assigned to receive 2 g of L-carnitine L-tartrate (LC) or placebo per day for 2 wk. Participants exercised for 90 min at 70% VO2max after 2 days of a prescribed diet (M ±SD: 13.6 ± 1.6 MJ, 57% carbohydrate, 15% protein, 26% fat, 2% alcohol) before and after supplementation. Results indicated no change in carbohydrate oxidation, nitrogen excretion, branched-chain amino acid oxidation, or plasma urea during exercise between the beginning and end of supplementation in either group. After 2 wk of LC supplementation the plasma ammonia response to exercise tended to be suppressed (0 vs. 2 wk at 60 min exercise, 97 ± 26 vs. 80 ± 9, and 90 min exercise, 116 ± 47 vs. 87 ± 25 μmol/L), with no change in the placebo group. The data indicate that 2 wk of LC supplementation does not affect fat, carbohydrate, and protein contribution to metabolism during prolonged moderate-intensity cycling exercise. The tendency toward suppressed ammonia accumulation, however, indicates that oral LC supplementation might have the potential to reduce the metabolic stress of exercise or alter ammonia production or removal, which warrants further investigation.