Carbohydrate supplementation during prolonged cycling exercise spares muscle glycogen but does not affect intramyocellular lipid use

Using contemporary stable-isotope methodology and fluorescence microscopy, we assessed the impact of carbohydrate supplementation on whole-body and fiber-type-specific intramyocellular triacylglycerol (IMTG) and glycogen use during prolonged endurance exercise. Ten endurance-trained male subjects were studied twice during 3 h of cycling at 63 ± 4% of maximal O2 uptake with either glucose ingestion (CHO trial; 0.7 g CHO kg−1 h−1) or without (CON placebo trial; water only). Continuous infusions with [U-13C] palmitate and [6,6-2H2] glucose were applied to quantify plasma free fatty acids (FFA) and glucose oxidation rates and to estimate intramyocellular lipid and glycogen use. Before and after exercise, muscle biopsy samples were taken to quantify fiber-type-specific IMTG and glycogen content. Plasma glucose rate of appearance (Ra) and carbohydrate oxidation rates were substantially greater in the CHO vs CON trial. Carbohydrate supplementation resulted in a lower muscle glycogen use during the first hour of exercise in the CHO vs CON trial, resulting in a 38 ± 19 and 57 ± 22% decreased utilization in type I and II muscle-fiber glycogen content, respectively. In the CHO trial, both plasma FFA Ra and subsequent plasma FFA concentrations were lower, resulting in a 34 ± 12% reduction in plasma FFA oxidation rates during exercise (P < 0.05). Carbohydrate intake did not augment IMTG utilization, as fluorescence microscopy revealed a 76 ± 21 and 78 ± 22% reduction in type I muscle-fiber lipid content in the CHO and CON trial, respectively. We conclude that carbohydrate supplementation during prolonged cycling exercise does not modulate IMTG use but spares muscle glycogen use during the initial stages of exercise in endurance-trained men

Metabolic Factors Limiting Performance in Marathon Runners

Each year in the past three decades has seen hundreds of thousands of runners register to run a major marathon. Of those who attempt to race over the marathon distance of 26 miles and 385 yards (42.195 kilometers), more than two-fifths experience severe and performance-limiting depletion of physiologic carbohydrate reserves (a phenomenon known as ‘hitting the wall’), and thousands drop out before reaching the finish lines (approximately 1–2% of those who start). Analyses of endurance physiology have often either used coarse approximations to suggest that human glycogen reserves are insufficient to fuel a marathon (making ‘hitting the wall’ seem inevitable), or implied that maximal glycogen loading is required in order to complete a marathon without ‘hitting the wall.’ The present computational study demonstrates that the energetic constraints on endurance runners are more subtle, and depend on several physiologic variables including the muscle mass distribution, liver and muscle glycogen densities, and running speed (exercise intensity as a fraction of aerobic capacity) of individual runners, in personalized but nevertheless quantifiable and predictable ways. The analytic approach presented here is used to estimate the distance at which runners will exhaust their glycogen stores as a function of running intensity. In so doing it also provides a basis for guidelines ensuring the safety and optimizing the performance of endurance runners, both by setting personally appropriate paces and by prescribing midrace fueling requirements for avoiding ‘the wall.’ The present analysis also sheds physiologically principled light on important standards in marathon running that until now have remained empirically defined: The qualifying times for the Boston Marathon

Effect of carbohydrate mouth rinsing on multiple sprint performance

BACKGROUND: Research suggests that carbohydrate mouth rinsing (CMR) improves endurance performance; yet, little is known regarding the effect of CMR on multiple sprint efforts. As many sports involve multiple sprinting efforts, followed by periods of recovery, the aim of our current study was to investigate the influence of CMR on multiple sprint performance. METHODS: We recruited eight active males (Age; 22 ± 1 y; 75.0 ± 8.8 kg; estimated VO2(max) 52.0 ± 3.0 ml/kg/min) to participate in a randomly assigned, double-blind, counterbalanced study administering a CMR (6.4% Maltodextrin) or similarly flavoured placebo solution. Primary outcomes for our study included: (a) time for three repeated sprint ability tests (RSA) and (b) the Loughborough Intermittent Shuttle Test (LIST). Time was expressed in seconds (sec). Secondary outcomes included ratings of perceived exertion (RPE) and blood glucose concentration. Tertiary outcomes included two psychological assessments designed to determine perceived activation (i.e., arousal) and pleasure-displeasure after each section of the LIST. We analysed our data using a two-way analysis of variance (ANOVA) for repeated measures, a Bonferroni adjusted post hoc t-test to determine significant differences in treatment, and a liberal 90% confidence interval between treatment conditions. Effect sizes were calculated between trials and interpreted as ≤ 0.2 trivial, > 0.2 small, > 0.6 moderate, > 1.2 large, > 2 very large and > 4 extremely large. Data are means ± SD. Overall statistical significance was set as P < 0.05; yet, modified accordingly when Bonferroni adjustments were made. RESULTS: Overall, we observed no significant difference in average (3.46 ± 0.2 vs. 3.44 ± 0.17; P = 0.11) or fastest time (3.38 ± 0.2 vs. 3.37 ± 0.2; P = 0.39) in the RSA test for the placebo vs. CMR conditions, respectively. Similar findings were also noted for the placebo vs. CMR, respectively, during the LIST test (3.52 ± 0.2 vs. 3.54 ± 0.2 sec; P = 0.63). Despite a significantly higher within group RPE during the 3rd and 4th sections of the LIST (< 0.05), no between group differences were otherwise noted. No differences were noted for blood glucose concentrations throughout the testing protocol. Lastly, from a psychological perspective, we observed no differences in pleasure-displeasure or perceived activation. CONCLUSIONS: The results of our current study suggest that CMR does not improve exercise performance, RPE or perceived pleasure-displeasure during high intensity activity requiring repeated, intermittent, sprint efforts

Effects of severity of long-standing congestive heart failure on pulmonary function

To investigate the effects of severity of long-standing congestive heart failure (CHF) on pulmonary function, we studied 53 (47 men) consecutive patients, all heart transplant candidates. Their mean (+/- SD) age and ejection fraction were 47 +/- 12 years and 23 +/- 7%, respectively. All patients underwent spirometry, lung volume, diffusion capacity (DLCO), maximum inspiratory (PImax) and expiratory pressure (PEmax) measurement. Maximum cardiopulmonary exercise test on a treadmill was also performed to determine maximum oxygen consumption ((V) over dot O(2)max). On the basis of (V) over dot O(2)max, the patients were then divided into those with a (V) over dot O(2)max 214 ml min(-1) kg(-1) (group 1, n = 30) and those with a (V) over dot O(2)max less than or equal to 14 mi min(-1) kg(-1) (group 2, n = 23). In comparison with group 1, group 2 patients had lower FEV1/FVC (70 +/- 8% vs 75 +/- 7%, P = 0.008), lower FEF25-75 (46 +/- 21 vs 70 +/- 26%pred, P &lt; 0.001), lower TLC (76 +/- 15 vs 85 +/- 13%pred, P = 0.02) and lower PImax (68 +/- 20 vs 87 +/- 22 cmH(2)O, P = 0.003), but comparable DLCO (84 +/- 15 vs 88 +/- 20%pred, P = N.S.), and PEmax (99 +/- 25 vs 96 +/- 22 cmH(2)O, P = N.S.). In conclusion, our data suggest that respiratory abnormalities, such as restrictive defects, airway obstruction, and inspiratory muscle weakness, are more pronounced in patients with severe CHF than in those with mild-to-moderate disease. Further studies are required to investigate the extent to which these abnormalities contribute to dyspnoea during daily activities in patients with heart failure

Contribution of lung function to exercise capacity in patients with chronic heart failure

Background: The importance of exercise capacity as an indicator of prognosis in patients with heart disease is well recognized. However, factors contributing to exercise limitation in such patients have not been fully characterized and in particular, the role of lung function in determining exercise capacity has not been extensively investigated. Objective: To examine the extent to which pulmonary function and respiratory muscle strength indices predict exercise performance in patients with moderate to severe heart failure. Methods: Fifty stable heart failure patients underwent a maximal symptom-limited cardiopulmonary exercise test on a treadmill to determine maximum oxygen consumption (VO2max), pulmonary function tests and maximum inspiratory (PImax) and expiratory (PEmax) pressure measurement. Results: In univariate analysis, VO2max correlated with forced vital capacity (r = 0.35, p = 0.01), forced expiratory volume in 1 s (r = 0.45, p = 0.001), FEV1/FVC ratio (r = 0.37, p = 0.009), maximal midexpiratory flow rate (FEF25-75, r = 0.47, p &lt; 0.001), and PImax (r = 0.46, p = 0.001), but not with total lung capacity, diffusion capacity or PEmax. In stepwise linear regression analysis, FEF25-75 and PImax were shown to be independently related to VO2max, with a combined r and r(2) value of 0.56 and 0.32, respectively. Conclusions: Lung function indices overall accounted for only approximately 30% of the variance in maximum exercise capacity observed in heart failure patients. The mechanism(s) by which these variables could set exercise limitation in heart failure awaits further investigation

Suplementação de carboidrato não reverte o efeito deletério do exercício de endurance sobre o subseqüente desempenho de força Suministrar carbohidratos no revierte el efecto destructivo del ejercicio de endurance sobre el subsiguiente desempeño de fuerza Carbohydrate supplementation fails to revert the deleterious effects of endurance exercise upon subsequent strength performance

Estudos disponíveis na literatura demonstram que a realização prévia de um exercício de endurance afeta de modo adverso o desempenho no exercício de força subseqüente. Tal ocorrência pode estar relacionada a mudanças metabólicas induzidas pelo exercício de endurance. O objetivo deste trabalho foi verificar se a ingestão de carboidrato (CHO) pode atenuar os efeitos de uma sessão aguda de exercício de endurance sobre o desempenho de força. A fim de testar essa hipótese, seis estudantes universitárias (164 ± 5,9cm; 64,9 ± 7,2kg), com experiência em treinamento de força, foram submetidas a um teste para a determinação do VO2pico (44 ± 4,3ml.min-1) e um teste de 1-RM para o leg press (186 ± 22,5kg) seguido de um teste de repetições máximas (duas séries de leg press realizado a 70% de 1-RM até exaustão 1ª série 21 ± 2,6 e 2ª série 11 ± 1,9 repetições) em dias diferentes. Seguindo um protocolo duplo-cego, os sujeitos foram submetidos a duas condições experimentais, recebendo uma bebida placebo (P) ou outra contendo carboidrato (6% - maltodextrina), antes (500ml) e durante (500ml) a realização de uma sessão de exercício de endurance (corrida em esteira 70% do VO2pico por 45 minutos). Em seguida ao exercício de endurance, os indivíduos realizaram um teste de 1-RM seguido pelo teste de repetições máximas. Não foram observadas mudanças no teste de 1-RM e na concentração plasmática de glicose entre as condições experimentais (P x CHO). O número de repetições máximas a 70%-1RM apresentou decréscimo nas duas situações (P 1ª série 13 ± 2,9 repetições e 2ª série 6 ± 2,1 repetições; CHO 1ª série 15 ± 2,5 repetições e 2ª série 7 ± 1,7 repetições, p < 0,05), não havendo diferença entre ambas. Uma sessão de exercício de endurance (intensidade moderada e longa duração) realizada previamente afeta de modo negativo a capacidade de realizar repetições máximas. Independente do mecanismo envolvido na redução do número de repetições máximas, o consumo de carboidrato foi incapaz de reverter esse efeito prejudicial.<br>Los estudios disponibles en la literatura demuestran que la realización previa de un ejercicio de endurance afecta de modo adverso el desempeño en el ejercicio de fuerza subsiguiente. Tal ocurrencia puede estar relacionada a cambios metabólicos inducidos por el ejercicio de endurance. Nuestro objetivo fue verificar si el ingerir carbohidratos (CHO) puede atenuar los efectos de una sesión aguda de ejercicio de endurance sobre el desempeño de fuerza. Con el fin de verificar esta hipótesis, 6 estudiantes universitarias (164 ± 5,9cm; 64,9 ± 7,2kg), con experiencia en entrenamiento de fuerza, fueron sometidas a un test para determinar el VO2pico (44 ± 4,3ml.min-1) y a un test de 1-RM para leg press (186 ± 22,5kg) seguido de un test de repeticiones máximas (2 series de leg press realizado a 70% de 1-RM hasta el cansancio 1ª serie 21 ± 2,6 y 2ª serie 11 ± 1,9 repeticiones) en días diferentes. Siguiendo un procedimiento doble-ciego los voluntarios fueron sometidos a dos condiciones experimentales, recibiendo una bebida placebo (P) u otra conteniendo carbohidratos (6% - maltodextrina), antes (500ml) y durante (500ml) la realización de una sesión de ejercicio de endurance (carrera en trotadores, 70% de VO2pico por 45 minutos). Después del ejercicio de endurance, los voluntarios realizaron un test de 1-RM seguido del test de repeticiones máximas. No se observaron cambios en el test de 1-RM o en la concentración plasmática de glicosis entre las condiciones experimentales (P x CHO). El número de repeticiones máximas a 70%-1RM presentó disminución en ambas situaciones (P 1ª serie 13 ± 2,9 reps y 2ª serie 6 ± 2,1 reps; CHO 1ª serie 15 ± 2,5 reps y 2ª serie 7 ± 1,7 reps, p < 0,05), no habiendo diferencia entre ellas. Una sesión de ejercicio de endurance (intensidad moderada) realizada previamente afecta de modo negativo la capacidad de repeticiones máximas. Independiente del mecanismo, el consumo de carbohidratos fue incapaz de revertir ese efecto perjudicial.<br>Previous studies indicated that endurance exercise might have an adverse effect on subsequent strength performance. The decrease in strength performance might be related to the changes promoted by endurance exercise in energy metabolism. Authors' aim was verify if carbohydrate (CHO) feeding can attenuate the effects of endurance exercise on strength development. To verify that hypothesis, six female university students (164 ± 5.9 cm; 64.9 ± 7.2 kg) with strength training experience were submitted to a VO2peak test (44 ± 4.3 ml.min-1) and an 1-RM test in the leg press (186 ± 22.5 kg) followed by a maximum repetitions test (2 sets of leg press exercise performed at 70% of 1-RM value until exhaustion, 1st set 21 ± 2.6 reps and 2nd set 11 ± 1.9 reps) in different days. In a double-blind design, the subjects were submitted to two different trials, receiving placebo (P) or CHO beverages (1 L of P or 6% maltodextrin solutions), 60 min before (500 ml) and during (500 ml) endurance exercise bout. These bouts were performed in a treadmill at 70% of VO2peak for 45 minutes. Subsequently, the subjects performed an 1-RM test followed by a maximum repetitions test. No changes were observed in 1-RM test. There was a similar decline in maximum repetitions test (an index of muscular endurance) in both trials (P - 1st set 13 ± 2.9 reps and 2nd set 6 ± 2.1 reps; CHO - 1st set 15 ± 2.5 reps and 2nd set 7 ± 1.7 reps, p < 0.05). Previous endurance exercise bout promoted deleterious effect upon muscular endurance task (maximum repetitions test - 70%-1-RM). CHO supplementation was inefficient to revert the effect of endurance exercise upon maximum repetitions test