L-arginine may enhance endurance performance mediated by two primary mechanisms including enhanced secretion of endogenous growth hormone (GH) and as a precursor of nitric oxide (NO); however, research in trained participants has been equivocal. The purpose was to investigate the effect of acute L-arginine ingestion on the hormonal and metabolic response during submaximal exercise in trained cyclists. Fifteen aerobically trained men (age: 28 ± 5 y; body mass: 77.4 ± 9.5 kg; height: 180.9 ± 7.9 cm; VO2max: 59.6 ± 5.9 ml·kg-1·min−1) participated in a randomized, double-blind, crossover study. Subjects consumed L-arginine (ARG; 0.075 g·kg-1 body mass) or a placebo (PLA) before performing an acute bout of submaximal exercise (60 min at 80% of power output achieved at ventilatory threshold). The ARG condition significantly increased plasma L-arginine concentrations (~146%), while no change was detected in the PLA condition. There were no differences between conditions for GH, nonesterified fatty acids (NEFA), lactate, glucose, VO2, VCO2, RER, CHO oxidation, and NOx. There was reduced fat oxidation at the start of exercise (ARG: 0.36 ± 0.25 vs. PLA: 0.42 ± 0.23 g·min−1, p < .05) and an elevated plasma glycerol concentrations at the 45-min time point (ARG: 340.3 vs. PLA: 288.5 μmol·L-1, p < .05) after L-arginine consumption. In conclusion, the acute ingestion of L-arginine did not alter any hormonal, metabolic, or cardio-respiratory responses during submaximal exercise except for a small but significant increase in glycerol at the 45-min time point and a reduction in fat oxidation at the start of exercise.
Scott C. Forbes, Vicki Harber and Gordon J. Bell
Emma Stevenson, Clyde Williams, Maria Nute, Peter Swaile and Monica Tsui
The present study investigated the effect of the glycemic index of an evening meal on responses to a standard high glycemic index (HGI) breakfast the following morning. The metabolic responses to exercise 3 h after breakfast were also investigated. Seven active males completed 2 trials. In each trial, participants were provided with an evening meal on day 1, which was composed of either HGI or LGI (high or low glycemic index) carbohydrates. On day 2, participants were provided with a standard HGI breakfast and then performed a 60 min run at 65% VO2max 3 h later. Plasma glucose and serum insulin concentrations following breakfast were higher in the HGI trial compared to the LGI trial (P < 0.05). During exercise, there were no differences in substrate utilization. The results suggest that consuming a single LGI evening meal can improve glucose tolerance at breakfast but the metabolic responses to subsequent exercise were not affected.
Elizabeth M. Broad, Ronald J. Maughan and Stuart D.R. Galloway
The effects of 15 d of supplementation with L-carnitine L-tartrate (LC) on metabolic responses to gradedintensity exercise under conditions of altered substrate availability were examined. Fifteen endurance-trained male athletes undertook exercise trials after a 2-d high-carbohydrate diet (60% CHO, 25% fat) at baseline (D0), on Day 14 (D14), and after a single day of high fat intake (15% CHO, 70% fat) on Day 15 (D15) in a double-blind, placebo-controlled, pair-matched design. Treatment consisted of 3 g LC (2 g L-carnitine/d; n = 8) or placebo (P, n = 7) for 15 d. Exercise trials consisted of 80 min of continuous cycling comprising 20-min periods at each of 20%, 40%, 60%, and 80% VO2peak. There was no significant difference between whole-body rates of CHO and fat oxidation at any workload between D0 and D14 trials for either the P or LC group. Both groups displayed increased fat and reduced carbohydrate oxidation between the D14 and D15 trials (p < .05). During the D15 trial, heart rate (p < .05 for 20%, 40%, and 60% workloads) and blood glucose concentration (p < .05 for 40% and 60% workloads) were lower during exercise in the LC group than in P. These responses suggest that LC may induce subtle changes in substrate handling in metabolically active tissues when fattyacid availability is increased, but it does not affect whole-body substrate utilization during short-duration exercise at the intensities studied.
Jens Bangsbo, Fedon Marcello Iaia and Peter Krustrup
The physical demands in soccer have been studied intensively, and the aim of the present review is to provide an overview of metabolic changes during a game and their relation to the development of fatigue. Heart-rate and body-temperature measurements suggest that for elite soccer players the average oxygen uptake during a match is around 70% of maximum oxygen uptake (VO2 max). A top-class player has 150 to 250 brief intense actions during a game, indicating that the rates of creatine-phosphate (CP) utilization and glycolysis are frequently high during a game, which is supported by findings of reduced muscle CP levels and several-fold increases in blood and muscle lactate concentrations. Likewise, muscle pH is lowered and muscle inosine monophosphate (IMP) elevated during a soccer game. Fatigue appears to occur temporarily during a game, but it is not likely to be caused by elevated muscle lactate, lowered muscle pH, or change in muscle-energy status. It is unclear what causes the transient reduced ability of players to perform maximally. Muscle glycogen is reduced by 40% to 90% during a game and is probably the most important substrate for energy production, and fatigue toward the end of a game might be related to depletion of glycogen in some muscle fibers. Blood glucose and catecholamines are elevated and insulin lowered during a game. The blood free-fatty-acid levels increase progressively during a game, probably reflecting an increasing fat oxidation compensating for the lowering of muscle glycogen. Thus, elite soccer players have high aerobic requirements throughout a game and extensive anaerobic demands during periods of a match leading to major metabolic changes, which might contribute to the observed development of fatigue during and toward the end of a game.
Blanche Evans, David Hopkins and Tracey Toney
The purpose of this study was to determine the metabolic stress of a self-paced half-mile walk test incorporated in the AAHPERD functional fitness assessment for older adults. Forty-three subjects, aged 57 to 75, completed a half-mile walk on an indoor track (IT) and during a treadmill simulation (TS) of the track walk. Treadmill data indicated that subjects exercised at a mean VO2 of 14.7 ml · kg−1 · min−1 and mean heart rate (b · min−1) of 129. A significant difference (p ≤ .05) was found between IT and TS on rating of perceived exertion. Results indicate that older subjects selected a pace that stressed their cardiorespiratory system without producing severe fatigue or medical complications. Therefore, the half-mile walk test appears to be a safe test that may be incorporated in functional fitness testing. However, its ability to determine functional capacity needs further study.
Anthony Couderc, Claire Thomas, Mathieu Lacome, Julien Piscione, Julien Robineau, Rémi Delfour-Peyrethon, Rachel Borne and Christine Hanon
To investigate the running demands and associated metabolic perturbations during an official rugby sevens tournament.
Twelve elite players participated in 7 matches wearing GPS units. Maximal sprinting speed (MSS) and maximal aerobic speed (MAS) were measured. High-intensity threshold was individualized relative to MAS (>100% of MAS), and very-high-intensity distance was reported relative to both MAS and MSS. Blood samples were taken at rest and after each match.
Comparison of prematch and postmatch samples revealed significant (P < .01) changes in pH (7.41–7.25), bicarbonate concentration ([HCO3–]) (24.8–13.6 mmol/L), and lactate concentration ([La]) (2.4–11.9 mmol/L). Mean relative total distance covered was 91 ± 13 m/min with ~17 m/min at high-intensity. Player status (whole-match or interchanged players), match time, and total distance covered had no significant impact on metabolic indices. Relative distance covered at high intensity was negatively correlated with pH and [HCO3–] (r = .44 and r = .42, respectively; P < .01) and positively correlated with [La] (r = .36; P < .01). Total distance covered and distance covered at very high intensity during the 1-min peak activity in the last 3 min of play were correlated with [La] (r = .39 and r = .39, respectively; P < .01).
Significant alterations in blood-metabolite indices from prematch to postmatch sampling suggest that players were required to tolerate a substantial level of acidosis related to metabolite accumulation. In addition, the ability to produce energy via the glycolytic energy pathway seems to be a major determinant in match-related running performance.
Herman-J. Engels and Emily M. Haymes
This study examined the effects of a single dose of caffeine (5 mg:kg−1) on energy metabolism during 60-min treadmill walking at light (30%
Martim Bottaro, Lee E. Brown, Rodrigo Celes, Saulo Martorelli, Rodrigo Carregaro and José Carlos de Brito Vidal
The purpose of this study was to compare the effect of different rest intervals and contraction velocities on muscle recovery following resistance exercise. 18 children (11.1 ± 0.52 yrs) and 19 adolescents (15.8 ± 0.49 yrs) performed three sets of 10 isokinetic repetitions at 60°/s and 180°/s. The work-to-rest ratio (W/R) was 1:2 and 1:4 for 60°/s, and 1:6 and 1:12 for 180°/s. ANOVA revealed that children demonstrated no significant decline in PT from the first to third set with any rest interval, but there was a significant (p < .05) decline for adolescents when a W/R of 1:2, 1:4 and 1:6 were used. Adolescents demonstrated significantly greater blood lactate (BLa) concentrations than children after three sets of resistance exercise. The present study indicates that adolescents may require longer rest intervals to recover full PT when compared with children.
Jonathan Watkins, Simon Platt, Erik Andersson and Kerry McGawley
The aim of the current study was to investigate pacing strategies and the distribution of physiological resources in best vs worst performances during a series of 4-min self-paced running time trials (RunTTs).
Five male and 5 female recreational runners (age 32 ± 7 y) completed a submaximal ramp test and 5 RunTTs on a motor-driven treadmill fitted with a speed-controlling laser system. The supramaximal oxygen-uptake (V̇O2) demand was estimated by linear extrapolation from the submaximal relationship between V̇O2 and speed, enabling computation of the accumulated oxygen deficit.
There were no significant differences between the 5 RunTTs for any of the performance, physiological, or subjective responses (P > .05). The trial-to-trial variability in pacing (ie, separate quarters) was typically low, with an average within-athlete coefficient of variation of 3.3%, being highest at the start and end of the 4 min. Total distance covered and distance covered over the first and last 2 min for best and worst performances were 1137 ± 94 and 1090 ± 89 (P < .001), 565 ± 53 and 526 ± 40 m (P = .002), and 572 ± 47 and 565 ± 54 m (P = .346), respectively.
Negative pacing strategies were evident during both the best and the worst performances of the RunTT. Best performances were characterized by more aggressive pacing over the first 2 min compared with worst performances. In addition, the relatively low trial-to-trial variability in running speed suggests that pacing strategies are similar during a series of 4-min self-paced running time trials.
Victoria L. Bowden and Robert G. McMurray
The purpose of this study was to determine if there is a difference between the way in which aerobically trained and untrained women metabolize fats and carbohydrates at rest in response to either a high-fat or high-carbohydrate meal. Subjects, 6 per group, were fed a high CHO meal (2068 kJ, 76% CHO. 23% fat, 5% protein) and a high fat meal (2093 kJ, 21% CHO, 72% fat, 8% protein) in counterbalanced order. Resting metabolic rate (RMR) was measured every half-hour for 5 hours. RMR was similar between groups. Training status had no overall effect on postprandial metabolic rate or total energy expenditure. The high fat meal resulted in no significant differences in RMR or respiratory exchange ratio (RER) between groups. However, after ingesting a high CHO meal, trained subjects had a peak in metabolism at minute 60, not evident in the untrained subjects. In addition, postprandial RER from minutes 120-300 were lower and fat use was greater after the high CHO meal for the trained subjects. These results suggest that aerobically trained women have an accelerated CHO uptake and overall lower CHO oxidation following the ingestion of a high CHO meal.