运动前进食不同血糖指数和血糖负荷膳食对男子长跑运动员运动耐力和免疫机能的影响

目的:探讨运动前2小时进食不同血糖指数(glycemic index,GI)和血糖负荷(glycemic load,GL)的含碳水化合物食物对运动耐力以及免疫机能的影响。方法:8名男子长跑耐力运动员(年龄24.3±2.2岁;体重66.7±2.0公斤;最大摄氧量55.9±1.9毫升.公斤-1体重.分钟-1),采用不完全随机的平衡重复测试方法随机完成三次耐力测试,每次测试间隔不少于7天。每次运动实验前两小时,受试者需进食等热量(每公斤体重约9千卡热量)的三种配餐之一,即高血糖指数高血糖负荷(H-H)、低血糖指数低血糖负荷(L-L)和高血糖指数低血糖负荷(H-L),其碳水化合物含量、GI和GL分别为65%、79.5、82.4(H-H);65%、40.2、42.1(L-L);15%、79.5、42.1(H-L)。每次测试中,受试者先在跑台上以70%VO2max强度、跑完1小时,接着以最短时间完成随后的10公里耐力跑。分别于运动前、70%VO2max运动1小时后即刻、完成10公里跑即刻,以及恢复期第1和第2小时末取静脉血测试免疫指标。结果:进食不同配餐后受试者的耐力表现无明显差异,完成10公里跑的时间分别为52.6±2.0分钟(H-H)、51.2±2.0分钟(L-L)和52.7±2.0分钟(H-L);运动后即刻和2小时恢复期中,与H-L膳食相比,H-H和L-L两种条件下受试者的外周血中淋巴细胞及中性粒细胞均减少,且运动结束后两小时的血浆白介素6、10和皮质醇浓度较低;运动60分钟后淋巴细胞增殖反应受抑制,并于运动结束后两小时恢复至基础水平,三种实验条件之间无明显差异。结果提示:运动前2小时进食不同血糖指数和血糖负荷碳水化合物饮食对之后的运动耐力表现无明显影响;与食物的血糖指数和血糖负荷相比,运动前饮食中的碳水化合物含量可能是影响耐力运动中免疫反应的更重要因子。     

Influence of high and low glycemic index meals on endurance running capacity

PURPOSE: The purpose of this study was to examine the effect of high and low glycemic index (GI) carbohydrate (CHO) pre-exercise meals on endurance running capacity. METHODS: Eight active subjects (five male and three female) ran on a treadmill at approximately 70% VO2max to exhaustion on two occasions separated by 7 d. Three hours before the run after an overnight fast, each subject was given in a single-blind, random order, isoenergetic meal of 850+/-21 kcal (mean+/-SEM; 67% carbohydrate, 30% protein, and 3% fat) containing either high (HGI) or low (LGI) GI carbohydrate foods providing 2.0 g CHO.kg(-1) body weight. RESULTS: Ingestion of the HGI meal resulted in a 580% and 330% greater incremental area under the 3-h blood glucose and serum insulin response curves, respectively. Performance times were not different between the HGI and LGI trials (113+/-4 min and 111+/-5 min, respectively). During the first 80 min of exercise in the LGI trial, CHO oxidation was 12% lower and fat oxidation was 118% higher than in the HGI trial. Although serum insulin concentrations did not differ between trials, blood glucose at 20 min into exercise in the HGI trial was lower than that during the LGI trial at the same time (3.6+/-0.3 mmol.L(-1) vs 4.3+/-0.3 mmol.L(-1); P < 0.05). During exercise, plasma glycerol and serum free fatty acid concentrations were lower in the HGI trial than in the LGI trial. CONCLUSIONS: This results demonstrate that although there is a relative shift in substrate utilization from CHO to fat when a low GI meal is ingested before exercise compared with that for a high GI meal, there is no difference in endurance running capacity.     

运动前进食不同血糖指数食物对长跑能力的影响

目的 :探讨运动前进食不同血糖指数食物对长跑能力的影响。方法 :实验设计采用平衡重复测试法 ,8名男子耐力长跑运动员在间隔期不少于 7天内 ,在隔夜空腹情况下分别进食含相等热量的低血糖指数 [Glycemicindex (GI) ](GI =37)或高GI(GI =77)的碳水化合物 (CHO)食物 (CHO∶1 5g/kg体重 )。 2小时后 ,受试者在水平跑台上进行 2 1km的长跑能力测试。首 5km中 ,受试者以其 70 %VO2 max的速度跑步 ,而其后的 16km ,则可随意选择速度以最短时间完成。结果 :与高GI试验相比 ,所有受试者在进食低GI食物后的跑步时间明显缩短 (98 7± 2 0vs 10 1 5± 2 1min ,P<0 0 1)。整个跑步全程中 ,低GI试验的血糖及血清游离脂肪酸 (FFA)的水平较高GI试验为高。虽然进食高GI食物后两小时的血清胰岛素较高 ,但在运动过程中 ,血清胰岛素、皮质醇、血乳酸水平与低GI试验相比均无显著差异。与高GI试验相比 ,低GI试验中CHO氧化在能量供应上的依赖低 9 5 % ,而脂肪氧化则高 17 9%。结论 :在运动前 2小时进食低血糖指数的CHO食物 ,比提供同等热量的高血糖指数食物能更有效地提高长跑运动的能力。     

Effect of frequency of carbohydrate feedings on recovery and subsequent endurance run

PURPOSE: This study examined the effect of feeding pattern of a high glycemic index (GI) meal during a short-term recovery on subsequent endurance capacity. METHODS: Eight men ran at 70% .VO2max on a level treadmill for 90 min (T1) on two occasions, followed by 4-h recovery (R) and a further exhaustive run at the same speed (T2). During the R, subjects consumed a prescribed meal with a GI of 77 in either a "gorging" (GOR) or "nibbling" (NIB) intake pattern, providing 1.5 g carbohydrate (CHO) per kilogram body mass. In the GOR trial, the foods were consumed in a single bolus, 20 min after the end of T1. In the NIB trial, the same quantity of food was ingested in three equal portions; the first consumed 20 min after the end of T1 and the remainder at hourly intervals thereafter. RESULTS: The run time during T2 was similar between trials (GOR vs NIB: 68.1 +/- 8.2 vs 66.8 +/- 8.7 min, P > 0.05). However, CHO utilization was lower and fat utilization higher during T2 in the GOR trial compared with the NIB trial (GOR vs NIB: CHO: 94.4 +/- 11.4 vs 117.6 +/- 10.6 g, P < 0.05; FAT: 55.9 +/- 8.0 vs 44 +/- 8.6 g, P < 0.01). CONCLUSIONS: These results suggest that serial consumption of a high GI meal during a 4-h recovery increased the reliance on CHO oxidation for energy provision during a subsequent run when compared with a single feeding. However, there was no difference in the duration of the exhaustive run after the recovery between the GOR and NIB trials.     

Effects of GI Meals on Intermittent Exercise

Pre-exercise meals or single foods containing low glycaemic index (LGI) carbohydrates (CHO) have been shown to enhance performance prior to prolonged steady state exercise compared to high glycaemic index (HGI) CHO. This study investigated the impact of HGI and LGI pre-exercise meals on intermittent high intensity exercise. Nine male recreational football players performed a football specific protocol followed by a 1 km time trial 3.5 h after ingesting 1 of 2 isoenergetic test meals (HGI: 870.3 kcal, LGI: 889.5 kcal), which were either HGI (GI: 80) or LGI (GI: 44). Blood glucose, fatty acids (FA), glycerol, β-hydroxybutyrate, lactate and insulin were assessed before, during, and after the exercise bout, whilst rates of CHO and fat oxidation were determined at 4 time points during the protocol. No significant differences were found for the 1 km time trial (LGI: 210.2±19.1 s: HGI: 215.8±22.6 s) (mean±SD), nor for any of the other variables measured (P>0.05) apart from a significant condition effect with FA and significant interaction effects observed for glucose, β-hydroxybutyrate and lactate (P<0.05). These findings suggest that the type of CHO ingested in a pre-match meal has no significant impact on performance or metabolic responses during 90 min of intermittent high intensity exercise.     

Increased fat availability enhances the capacity of trained individuals to perform prolonged exercise

METHODS: After a familiarization period, six well-trained males participated in a diet and exercise regimen lasting 9 d and comprising three cycling tests to exhaustion. A work rate was selected during the familiarization period that would result in fatigue after approximately 90-100 min at an ambient temperature of 10 degrees C (i.e., approximately 75% of VO2max). The first exercise test was a depletion trial and was preceded by a period during which the subjects' normal diet was consumed. A prescribed 70% carbohydrate (CHO) diet was then consumed for 3.5 d. After this diet, a second exercise test was performed; one of two isoenergetic experimental meals was consumed 4 h before this test (70% CHO meal, CHO trial; or 90% fat meal, fat trial). The second exercise test was followed by a further 3.5-d period on the high CHO diet. Four hours before the third test, subjects consumed the other meal. Heparin was administered intravenously 30 min (1000 U), 15 min (500 U), and 0 min (500 U) before exercise on the fat trial. Subjects were assigned to the two meals in randomized order. RESULTS: Time to exhaustion increased from 118.2 (12.4) min on the CHO trial to 127.9 (12.1) min on the fat trial (P = 0.001). Although no difference in VO2, RER, HR or RPE was found between trials, there was an earlier reduction in RER and an earlier rise in RPE on the fat trial. No difference in total CHO oxidation was found between trials (383 +/- 70 g on the CHO trial and 362 +/- 59 g on the fat trial). CONCLUSIONS: These results suggest that increasing fat availability immediately before exercise by acute fat feeding and heparin infusion can improve endurance exercise in a cool environment in well-trained individuals. This study was not intended to have immediate application to the sports performance field but rather to contribute to our understanding of the factors that may limit endurance performance. Heparin injection to elevate plasma fatty acid concentration would not represent sound medical practice.     

Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability.

PURPOSE: Five days of a high-fat diet produce metabolic adaptations that increase the rate of fat oxidation during prolonged exercise. We investigated whether enhanced rates of fat oxidation during submaximal exercise after 5 d of a high-fat diet would persist in the face of increased carbohydrate (CHO) availability before and during exercise. METHODS: Eight well-trained subjects consumed either a high-CHO (9.3 g x kg(-1) x d(-1) CHO, 1.1 g x kg(-1) x d(-1) fat; HCHO) or an isoenergetic high-fat diet (2.5 g x kg(-1) x d(-1) CHO, 4.3 g x kg(-1) x d(-1) fat; FAT-adapt) for 5 d followed by a high-CHO diet and rest on day 6. On day 7, performance testing (2 h steady-state (SS) cycling at 70% peak O(2) uptake [VO(2peak)] + time trial [TT]) of 7 kJ x kg(-1)) was undertaken after a CHO breakfast (CHO 2 g x kg(-1)) and intake of CHO during cycling (0.8 g x kg(-1) x h(-1)). RESULTS: FAT-adapt reduced respiratory exchange ratio (RER) values before and during cycling at 70% VO(2peak); RER was restored by 1 d CHO and CHO intake during cycling (0.90 +/- 0.01, 0.80 +/- 0.01, 0.91 +/- 0.01, for days 1, 6, and 7, respectively). RER values were higher with HCHO (0.90 +/- 0.01, 0.88 +/- 0.01 (HCHO > FAT-adapt, P < 0.05), 0.95 +/- 0.01 (HCHO > FAT-adapt, P < 0.05)). On day 7, fat oxidation remained elevated (73 +/- 4 g vs 45 +/- 3 g, P < 0.05), whereas CHO oxidation was reduced (354 +/- 11 g vs 419 +/- 13 g, P < 0.05) throughout SS in FAT-adapt versus HCHO. TT performance was similar for both trials (25.53 +/- 0.67 min vs 25.45 +/- 0.96 min, NS). CONCLUSION: Adaptations to a short-term high-fat diet persisted in the face of high CHO availability before and during exercise, but failed to confer a performance advantage during a TT lasting approximately 25 min undertaken after 2 h of submaximal cycling.     

The effect of two sports drinks and water on GI complaints and performance during an 18-km run

Gastrointestinal (GI) complaints are frequently experienced during running. Sports drinks to prevent dehydration and hypoglycemia during exercise are generally used. The aim was to investigate the effect of 3 different drinks on GI complaints and performance during competitive running in a controlled field study. Ninety-eight well-trained subjects (90 M, 8 F, age 41 +/- 8 y) performed a competitive 18-km run three times within 8 days. The study was a controlled, standardized field experiment following a randomized, crossover design. Three different drinks were compared: water, a sports drink (CES), and a sports drink with added 150 mg/l caffeine (CAF). The incidence of GI complaints and the effect of the drinks on performance was studied. Each subject consumed 4 times 150 ml as follows: at the start, after 4.5 km, 9 km, and 13.5 km. Fluid intake was controlled. Incidence and intensity of GI complaints during the run were determined using a 10 points scale questionnaire. There were no significant differences in performance between the 3 drinks. Run time (18 km, mean +/- SD): WAT 1 : 18 : 03 +/- 08 : 30, CES 1 : 18 : 23 +/- 08 : 47, CAF 1 : 18 : 03 +/- 08 : 42. The use of carbohydrate-containing sports drinks led to higher incidences of all types of GI complaints compared to water. Significant differences (p < 0.05) were reached for flatulence; incidence: WAT 17.9 %, CES 28.6 %, CAF 30.6 %, and reflux; incidence: WAT 55.7 %, CES 78.6 %, CAF 72.5 %. There were no significant differences in intensity of the GI complaints. Addition of caffeine to CES had no effect on GI complaints, compared to CES alone. We conclude that sports drinks used during an 18-km run in cool environmental conditions do not support the performance better than mineral water. The use of sports drinks during an 18-km run leads to a higher incidence of both upper and lower GI complaints compared to water. Addition of caffeine to the sports drink has no effect on either running performance or GI complaints.     

Failure of protein to improve time trial performance when added to a sports drink

INTRODUCTION: Recent studies have reported that adding approximately 2% protein to a carbohydrate sports drink increased cycle endurance capacity compared with carbohydrate alone. However, the practical implications of these studies work are hampered by the following limitations: (a) the rate of carbohydrate ingestion was less than what is considered optimal for endurance performance, and (b) the performance test (exercise time to fatigue) did not mimic the way in which athletes typically compete (i.e., a race in which a fixed distance or set amount of work is performed as quickly as possible). PURPOSE: We tested the hypothesis that adding 2% protein to a 6% carbohydrate drink (CHO-PRO) would improve 80-km cycling time trial performance, as compared with a 6% carbohydrate drink (CHO) and a nonenergetic sweetened placebo (PLAC). METHODS: Ten trained male cyclists (24 +/- 2 yr; VO2peak = 63 +/- 2 mL.kg(-1).min(-1); mean +/- SE) performed an 80-km laboratory time trial (TT) on three occasions separated by 7 d. In a double-blind crossover manner, subjects ingested CHO-PRO, CHO, or PLAC at a rate of 250 mL every 15 min with no temporal, verbal, or physiological feedback. RESULTS: Time to complete the TT was 4.4% lower (P < 0.002) during CHO (135 +/- 9 min) and CHO-PRO (135 +/- 9) compared with PLAC (141 +/- 10), with no difference between CHO and CHO-PRO (P = 0.92). CONCLUSION: Ingesting 6% carbohydrate at a rate of 1 L.h(-1) (60 g.h(-1)) improved an 80-km TT performance in trained male cyclists. However, adding 2% protein to a 6% carbohydrate drink provided no additional performance benefit during a task that closely simulated the manner in which athletes typically compete.     

Effect of dietary fat on serum and intramyocellular lipids and running performance

PURPOSE: This study evaluated whether lowering IMCL stores via 3-d consumption of very-low-fat (LFAT) diet impairs endurance performance relative to a moderate-fat diet (MFAT), and whether such a diet unfavorably alters lipid profiles. METHODS: Twenty-one male and female endurance-trained runners followed a controlled diet and training regimen for 3 d prior to consuming either a LFAT (10% fat) or MFAT (35% fat) isoenergetic diet for another 3 d in random crossover fashion. On day 7, runners followed a glycogen normalization protocol (to equalize glycogen stores) and then underwent performance testing (90-min preload run at 62 +/- 1% VO2max followed by a 10-km time trial) on the morning of day 8. Muscle biopsies obtained from vastus lateralis before and after performance testing were analyzed for IMCL (via electron microscopy) and glycogen content (via enzymatic methodology). RESULTS: Despite approximately 30% lower IMCL (0.220 +/- 0.032% LFAT, 0.316 +/- 0.049% MFAT; P = 0.045) and approximately 22% higher muscle glycogen stores at the start of performance testing (P = 0.10), 10-km performance time was not significantly different following the two diet treatments (43.5 +/- 1.4 min LFAT vs 43.7 +/- 1.2 min MFAT). However, LFAT produced less favorable lipid profiles (P < 0.01) by increasing fasting triglycerides (baseline = 84.9 +/- 8.6; LFAT = 118.7 +/- 10.0 mg.dL(-1)) and the total cholesterol:HDL cholesterol ratio (baseline = 3.42 +/- 0.13:1; LFAT = 3.75 +/- 0.20:1), whereas MFAT lowered triglycerides (baseline = 97.5 +/- 12.2; MFAT = 70.9 +/- 7.1 mg.dL(-1)) and the total cholesterol:HDL cholesterol ratio (baseline = 3.47 +/- 0.18:1; MFAT = 3.33 +/- 0.14:1). CONCLUSION: The results suggest that reducing IMCL via 3-d consumption of a LFAT diet does not impair running performance lasting a little over 2 h (compared with 3-d consumption of a MFAT diet plus 1-d glycogen normalization), but that even short-term consumption of a LFAT diet may unfavorably alter serum lipids, even in healthy, endurance-trained runners.     

The effect of glucose infusion on glucose kinetics during a 1-h time trial

PURPOSE AND METHODS: To investigate the effect of glucose infusion on glucose kinetics and performance, six endurance cyclists (VO2max = 61.7 +/- 2.0 (mean +/- SE) mL x kg(-1) x min(-1)) completed two performance trials in which they had to accomplish a set amount of work as quickly as possible (991 +/- 41 kJ). Subjects were infused with either glucose (20% in saline; carbohydrate (CHO)) at a rate of 1 g x min(-1) or saline (0.9% saline; placebo (PLA)). It was hypothesized that time trial performance would be unaffected by the infusion of glucose, as endogenous stores of CHO would not be limiting in the PLA trial. RESULTS: Plasma glucose concentration increased from 4.8 +/- 0.1 mmol x L(-1) to 5.9 +/- 0.3 mmol x L(-1) during the PLA trial and from 4.9 +/- 0.1 mmol x L(-1) at rest to 12.4 +/- 1.1 mmol x L(-1) during the CHO trial. These values were significantly higher at all time points during the CHO trial compared with PLA (P < 0.001). In the final stages of the time trial, Rd in the PLA trial was 49 +/- 5 micromol x kg(-1) x min(-1) compared with 88 +/- 7 micromol x kg(-1) x min(-1) in the CHO trial (P < 0.05). Despite these differences, there was no difference in performance time between PLA and CHO (60.04 +/- 1.47 min, PLA, vs 59.90 +/- 1.49 min, CHO, respectively). Infused carbohydrate oxidation in the last 25% of the CHO trial was at least 675 +/- 120 micromol x kg(-1) and contributed 17 +/- 4% to total carbohydrate oxidation. CONCLUSION: The results demonstrate that glucose infusion had no effect on 1-h cycle time-trial performance, despite an increased availability of plasma glucose for oxidation and evidence of increased glucose uptake into the tissues.     

Reproducibility of endurance performance on a treadmill using a preloaded time trial

PURPOSE: The purpose of this study was to establish a highly reproducible test to measure endurance performance in runners. METHODS: We evaluated the reproducibility of endurance performance during a 10-km time trial performed on a treadmill after a 90-min preload run at 65% of maximal oxygen uptake VO2max). After screening and a practice test, eight endurance runners (4 men, 4 women, 33.4 +/- 10.1 yr, VO2max = 60.3 +/- 6.3 mL x kg(-1) x min(-1) in men and 51.8 +/- 2.2 mL x kg(-1) x min(-1) in women, mean +/- SD) completed two preloaded time trial tests spaced 3-4 wk apart in men and one menstrual cycle apart in women. A high-carbohydrate diet (15% protein, 10% fat, 75% carbohydrate) was provided the day before both tests. RESULTS: Runners completed time trial 1 and time trial 2 in 45:41 +/- 4:45 and 45:24 +/- 5:03 min:s, respectively (43:29 +/- 5:02 and 43:12 +/- 5:14 min:s for men and 47:53 +/- 3:47 and 47:35 +/- 4:23 min:s for women, trials 1 and 2, respectively). The within-subject coefficient of variation for 10-km time was 1.00% +/- 0.25% (point estimate +/- estimated standard error) (0.54% +/- 0.19% for men and 1.26% +/- 0.45% for women). CONCLUSION: These results suggest that performance measured as time to complete a 10-km time trial on a treadmill after a 90-min preload is extremely reliable and may be useful for future research assessing the effect of diet, ergogenic substances, or training methods on endurance running performance.     

Effect of an isocaloric carbohydrate-protein-antioxidant drink on cycling performance

PURPOSE: Fourteen male cyclists were studied to compare the effect of carbohydrate-protein-antioxidant beverage (CHOPA) to an isocaloric carbohydrate-only (CHO) beverage on time to fatigue and muscle damage. METHODS: Subjects performed two sets of rides to exhaustion on a cycle ergometer. In each set, the first ride was performed at 70% VO2peak, and the second was performed 24 h later at 80%. CHO or CHOPA was consumed every 15 min during exercise and immediately afterward. Plasma CK and LDH and muscle soreness were measured pre- and postexercise. RESULTS: Time to fatigue was not different between CHO and CHOPA at 70% VO2peak (95.8 +/- 29.7 vs 98.1 +/- 28.7 min), 80% VO2peak (42.3 +/- 18.6 vs 42.9 +/- 21.8 min), or total performance time (138.1 +/- 39.3 vs 140.9 +/- 43.7 min). Postexercise CK was increased (P < 0.05) from baseline in CHO (203 +/- 120 vs 582 +/- 475 U.L(-1)) but not with CHOPA (188 +/- 119 vs 273 +/- 169 U.L(-1)). Similarly, LDH values increased over baseline in CHO (437 +/- 46 vs 495 +/- 64 U.L(-1)) but not with CHOPA (432 +/- 40 vs 451 +/- 43 U.L(-1)). Postexercise CPK and LDH were higher after the CHO trial than after the CHOPA trial. Median postexercise muscle soreness was higher in CHO (3.0 +/- 5.0) than with CHOPA (1.0 +/- 3.0). CONCLUSION: No differences in time to fatigue were observed between the beverages, despite lower total carbohydrate content in the CHOPA beverage. The CHOPA beverage attenuated postexercise muscle damage, as evidenced by CK and LDH values, compared with an isocaloric CHO beverage.     

Branched-chain amino acids supplementation attenuates the accumulation of blood lactate dehydrogenase during distance running

AIM: We investigated the effect of branched-chain amino acids (BCAA) supplementation on tissue damage during distance running. METHODS: Eight male distance runners (mean +/- standard deviation; age: 20.4+/-1.2 years, body weight: 58.4+/-4.2 kg) participated in a double blinded cross over designed study conducted during training camp. During each intervention period, the subjects were asked to participate in a 25-km run, and the blood BCAA and lactate dehydrogenase (LDH) level, an index of tissue damage, were measured pre- and post-run. Either a drink containing BCAA (0.4% BCAA in a 4% carbohydrate solution) or an iso-calorie placebo drink was provided to the subjects 5 times during the run without any restriction in the volume. RESULTS: The total volume of the drink consumed by the subjects did not differ substantially between the trials: 591+/-188 (2.36 g BCAA) vs 516+/-169 mL in BCAA and placebo trial, respectively. During the run, the blood BCAA concentration was maintained in the BCAA trial. However, the blood BCAA concentration level tended to decrease in the placebo trial (P<0.1). The extent of the blood LDH increase in the BCAA trial was significantly less than that of the placebo trail (48% vs 58%, P<0.05). CONCLUSION: Maintaining the blood BCAA level throughout a long distance run contributes to a reduction in the LDH release and, therefore, the effect of BCAA supplementation is suggested to reduce the degree of muscle damage.     

Effects of ingesting a sports bar versus glucose polymer on substrate utilisation and ultra-endurance performance.

The purpose of this study was to determine whether the ingestion of a sports bar (BAR) containing a mixture of fat (7 g), protein (14 ) and carbohydrate (CHO; 19 ) improved ulta-endurance cycling performance compared to when an equicaloric amount of CHO was consumed. On two occasions separated by a minimum of 7 days, six highly trained (peak power output [PPO] 414 +/- 8 W) endurance cyclists rode for 330 min at approximately 50% of PPO (203 +/- 8 W) while ingesting either the BAR or just CHO, before performing a 400 k] time trial as fast as possible. Rates of fat oxidation were significantly greater at the end of the submaximal ride when subjects ingested the BAR compared to CHO (1.09 +/- 0.08 vs 0.73 +/- 0.08g x min(-1); P<0.05), and accordingly total fat oxidation was significantly higher (280 +/- 24 vs 203 +/- 25 g, P < 0.05). However, two subjects failed to complete the time trial after they consumed the BAR during the prolonged, submaximal ride, whereas all subjects managed to finish the time trial when ingesting CHO. In conclusion, ingestion of the sports bar enhanced fat metabolism during prolonged, submaximal exercise, but impaired subsequent high-intensity time-trial performance.     

The effect of carbohydrate mouth rinse on 1-h cycle time trial performance

PURPOSE AND METHOD: To investigate the possible role of carbohydrate (CHO) receptors in the mouth in influencing exercise performance, seven male and two female endurance cyclists (VO(2max) 63.2 +/- 2.7 (mean +/- SE) mL.kg*(-1).min(-1)) completed two performance trials in which they had to accomplish a set amount of work as quickly as possible (914 +/- 40 kJ). On one occasion a 6.4% maltodextrin solution (CHO) was rinsed around the mouth for every 12.5% of the trial completed. On the other occasion, water (PLA) was rinsed. Subjects were not allowed to swallow either the CHO solution or water, and each mouthful was spat out after a 5-s rinse. RESULTS: Performance time was significantly improved with CHO compared with PLA (59.57 +/- 1.50 min vs 61.37 +/- 1.56 min, respectively, P = 0.011). This improvement resulted in a significantly higher average power output during the CHO compared with the PLA trial (259 +/- 16 W and 252 +/- 16 W, respectively, P = 0.003). There were no differences in heart rate or rating of perceived exertion (RPE) between the two trials (P > 0.05). CONCLUSION: The results demonstrate that carbohydrate mouth rinse has a positive effect on 1-h time trial performance. The mechanism responsible for the improvement in high-intensity exercise performance with exogenous carbohydrate appears to involve an increase in central drive or motivation rather than having any metabolic cause. The nature and role of putative CHO receptors in the mouth warrants further investigation.     

Effects of respiratory muscle endurance training on wheelchair racing performance in athletes with paraplegia: a pilot study.

OBJECTIVE: Respiratory muscle endurance training (RMET) has been shown to improve both respiratory muscle and cycling exercise endurance in able-bodied subjects. Since effects of RMET on upper extremity exercise performance have not yet been investigated, we evaluated the effects of RMET on 10-km time-trial performance in wheelchair racing athletes. DESIGN: Pilot study, controlled before and after trial. SETTING: Spinal cord injury research center. PARTICIPANTS: 12 competitive wheelchair racing athletes. INTERVENTIONS: The training group performed 30 sessions of RMET for 30 min each. The control group did no respiratory muscle training. MAIN OUTCOME MEASUREMENTS: Differences in 10-km time-trial performance pre- versus postintervention. RESULTS: In the training group, the time of the 10-km time-trial decreased significantly from before versus after intervention (27.1 +/- 9.0 vs. 24.1 +/- 6.6 min); this did not occur in the control group (23.3 +/- 2.8 vs. 23.2 +/- 2.4 min). No between groups difference was present (P = 0.150). Respiratory muscle endurance increased significantly within the training group (9.1 +/- 7.2 vs. 39.9 +/- 17.8 min) and between groups, but not within the control group (4.3 +/- 2.9 vs. 6.6 +/- 7.0 min) before versus after intervention. CONCLUSION: There was a strong trend, with a large observed effect size of d = 0.87, towards improved performance in the 10-km time-trial after 6 weeks of RMET.     

Pre-exercise carbohydrate and fluid ingestion: influence of glycemic response on 10-km treadmill running performance in the heat

BACKGROUND: The purpose of this study was to determine the influence of ingesting solutions containing mixtures of carbohydrate (CHO) types on pre-exercise glycemic response, exercise-induced hypoglycemia, metabolic responses, and 10-km treadmill running performance in a warm environment. METHODS: Ten trained runners completed 6, self-paced 10-km treadmill runs one hour after ingesting 900 ml of one of the following test solutions: a water placebo (WP), an 8 g 100 ml-1 high fructose corn syrup solution (HFG; 72 g CHO), a 6 g 100 ml-1 glucose solution (GLU; 54 g CHO), a 6 g.100 ml-1 sucrose/glucose mixture (SUG; 54 g CHO), or banana with water to equal 900 ml (BAN; approx. 54 g CHO). The sixth condition was 675 ml of an 8 g.100 ml-1 HFCS solution (LFG; 54 g CHO). Blood samples were taken prior to ingestion and every 15 min during rest and at 15 and 30 min, and at the end of the 10-km run. Blood was analyzed for glucose (BG) insulin (IN), glycerol, lactate, and percent change in plasma volume. Urine volume during the 1 hour of rest and change in body mass during exercise were also determined. RESULTS: A significant (p < 0.05) correlation (r = -0.684) was seen between the pre-exercise glycemic response (PEGR = area under the resting BG curve) and the change in BG from pre-EX to 15 min of exercise. BG at 15 min of exercise was significantly higher in the WP (5.22 mM) versus the other conditions (HFG = 3.32, LFG = 3.91, GLU = 3.38, BAN = 3.74 & SUG = 3.63 mM). Pre-exercise IN was lower in the WP (6.54 U ml-1) condition versus the other conditions (HFG = 22.1, LFG = 16.2, GLU = 23.3, BAN = 18.8 & SUG = 12.8 U.ml-1). Ten km performance times were not different (WP = 41.87, HFG = 41.66, LFG = 41.79, GLU = 41.65, BAN = 41.53, and SUG = 41.75 min). A significantly greater body mass loss occurred due to urine production during the 60 min of rest in the WP compared to the other conditions. The degree of exercise-induced decline in blood glucose was related to the PEGR; however, the decline in BG did not affect 10-km running performance. In addition, there were no differences in the metabolic responses during exercise between the different CHO types, nor did the type of CHO influence running performance. Finally, the presence of CHO and/or electrolytes in the hydration solutions produced a better fluid retention during the 60-min pre-exercise rest period compared to water. CONCLUSIONS: The results confirmed that if a competitive athlete consumed a breakfast prior to ingesting a CHO-electrolyte beverage, a practice that is common, the glycemic responses may be different.     

Physical and training characteristics of top-class marathon runners.

PURPOSE: This study compares the physical and training characteristics of top-class marathon runners (TC), i.e., runners having a personal best of less than 2 h 11 min for males and 2 h 32 min for females, respectively, versus high-level (HL) (< 2 h 16 min and < 2 h 38 min). METHODS: Twenty marathon runners (five TC and HL in each gender) ran 10 km at their best marathon performance velocity (vMarathon) on a level road. This velocity was the target velocity for the Olympic trials they performed 8 wk later. After a rest of 6 min, they ran an all-out 1000-m run to determine the peak oxygen consumption on flat road (.VO(2peak)). RESULTS: Marathon performance time (MPT) was inversely correlated with .VO(2peak). (r = -0.73, P < 0.01) and predicted 59% of the variance of MPT. Moreover, TC male marathon runners were less economical because their energy cost of running (Cr) at marathon velocity was significantly higher than that of their counterparts (212 +/- 17 vs 195 +/- 14 mL.km(-1).kg(-1), P = 0.03). For females, no difference was observed for the energetic characteristics between TC and HL marathon runners. However, the velocity reached during the 1000-m run performed after the 10-km run at vMarathon was highly correlated with MPT (r = -0.85, P < 0.001). Concerning training differences, independent of the gender, TC marathon runners trained for more total kilometers per week and at a higher velocity (velocity over 3000 m and 10,000 m). CONCLUSION: The high energy output seems to be the discriminating factor for top-class male marathon runners who trained at higher relative intensities.     

Effect of carbohydrate feedings on muscle glycogen utilization and exercise performance

Ten men were studied during 4 h of cycling to determine the effect of solid carbohydrate (CHO) feedings on muscle glycogen utilization and exercise performance. In the experimental trial (E) the subjects ingested 43 g of sucrose in solid form along with 400 ml of water at 0, 1, 2 and 3 h of exercise. During the control trial (C) they received 400 ml of an artificially sweetened drink without solid CHO. No differences in VO2, heart rate, or total energy expenditure were observed between trials; however, respiratory exchange ratios were significantly (P less than 0.05) higher during E. Blood glucose was significantly (P less than 0.05) elevated 20 min post-feeding in E; however, by 50 min no differences were observed between trials until 230 min (E = 4.5 +/- 0.2 mmol X l-1 vs C = 3.9 +/- 0.2, means +/- SE; P less than 0.05). Muscle glycogen utilization was significantly (P less than 0.05) lower during E (100.7 +/- 10.2 mmol X kg-1 w.w.) than C (126.2 +/- 5.5). During a sprint (100% VO2max) ride to exhaustion at the end of each trial, subjects performed 45% longer when fed CHO (E = 126.8 +/- 24.7 s vs C = 87.2 +/- 17.5; P less than 0.05). It was concluded that repeated solid CHO feedings maintain blood glucose levels, reduce muscle glycogen depletion during prolonged exercise, and enhance sprint performance at the end of such activity.