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1.
The purpose of this study was to examine the influence of a carbohydrate-rich meal on post-prandial metabolic responses and skeletal muscle glycogen concentration. After an overnight fast, eight male recreational/club endurance runners ingested a carbohydrate (CHO) meal (2.5 g CHO?·?kg?1 body mass) and biopsies were obtained from the vastus lateralis muscle before and 3 h after the meal. Ingestion of the meal resulted in a 10.6?±?2.5% (P?<?0.05) increase in muscle glycogen concentration (pre-meal vs post-meal: 314.0?±?33.9 vs 347.3?±?31.3 mmol?·?kg?1 dry weight). Three hours after ingestion, mean serum insulin concentrations had not returned to pre-feeding values (0 min vs 180 min: 45?±?4 vs 143?±?21 pmol?·?l?1). On a separate occasion, six similar individuals ingested the meal or fasted for a further 3 h during which time expired air samples were collected to estimate the amount of carbohydrate oxidized over the 3 h post-prandial period. It was estimated that about 20% of the carbohydrate consumed was converted into muscle glycogen, and about 12 % was oxidized. We conclude that a meal providing 2.5 g CHO?·?kg?1 body mass can increase muscle glycogen stores 3 h after ingestion. However, an estimated 67% of the carbohydrate ingested was unaccounted for and this may have been stored as liver glycogen and/or still be in the gastrointestinal tract.  相似文献   

2.
Ingesting carbohydrate plus protein following prolonged exercise may restore exercise capacity more effectively than ingestion of carbohydrate alone. The objective of the present study was to determine whether this potential benefit is a consequence of the protein fraction per se or simply due to the additional energy it provides. Six active males participated in three trials, each involving a 90-min treadmill run at 70% maximal oxygen uptake (run 1) followed by a 4-h recovery. At 30-min intervals during recovery, participants ingested solutions containing: (1) 0.8 g carbohydrate x kg body mass (BM)(-1) h(-1) plus 0.3 g kg(-1) h(-1) of whey protein isolate (CHO-PRO); (2) 0.8 g carbohydrate x kg BM(-1) h(-1) (CHO); or (3) 1.1 g carbohydrate x kg BM(-1) h(-1) (CHO-CHO). The latter two solutions matched the CHO-PRO solution for carbohydrate and for energy, respectively. Following recovery, participants ran to exhaustion at 70% maximal oxygen uptake (run 2). Exercise capacity during run 2 was greater following ingestion of CHO-PRO and CHO-CHO than following ingestion of CHO (P< or = 0.05) with no significant difference between the CHO-PRO and CHO-CHO treatments. In conclusion, increasing the energy content of these recovery solutions extended run time to exhaustion, irrespective of whether the additional energy originated from sucrose or whey protein isolate.  相似文献   

3.
Abstract

Both carbohydrate depletion and dehydration have been shown to decrease performance whilst severe dehydration can also cause adverse health effects. Therefore carbohydrate and fluid requirements are increased with exercise. Ingestion of 200–300?g of CHO 3–4?h prior to exercise is an effective strategy in order to meet daily CHO demands and increase CHO availability during the subsequent exercise period. There is little evidence that CHO during the hour immediately prior to exercise has adverse effects such as rebound hypoglycaemia. CHO ingestion during exercise has been shown to improve performance as measured by enhanced work output or decreased exercise time to complete a fixed amount of work. Recent studies have demonstrated that exogenous CHO oxidation rates can be increased by ingesting combinations of CHO that use different intestinal CHO transporters. After exercise maximal muscle glycogen re-synthesis rates can be achieved by ingesting CHO at a rate of ～1.2?g/kg/h, in relatively frequent (e.g., 15–30?min) intervals for up to 5?h following exercise. Protein amino acid mixtures may increase glycogen synthesis further but only if relatively small amounts of CHO are ingested.

Hypohydration and hyperthermia alone have negative effects on performance but their combination is particularly serious, both in terms of performance and health. Dehydration can be prevented by fluid ingestion pre exercise and during exercise. Because of large individual differences it is difficult to individualise the advice. Perhaps the best guidance for athletes is to weigh themselves to assess fluid losses during training and racing and limit weight losses to 1% during exercise lasting longer than 1.5?h. Excessive fluid intake has been associated with hyponatremia. Post exercise the volume of fluid ingested and sodium intake are important determinants of rehydration.  相似文献   

4.
The aim of the present study was to examine the effect of ingesting 75 g of glucose 45 min before the start of a graded exercise test to exhaustion on the determination of the intensity that elicits maximal fat oxidation (Fatmax). Eleven moderately trained individuals (VO2max: 58.9 +/- 1.0 ml x kg(-1) x min(-1); mean +/- sx), who had fasted overnight, performed two graded exercise tests to exhaustion, one 45 min after ingesting a placebo drink and one 45 min after ingesting 75 g of carbohydrate in the form of glucose. The tests started at 95 W and the workload was increased by 35 W every 3 min. Gas exchange measures and heart rate were recorded throughout exercise. Fat oxidation rates were calculated using stoichiometric equations. Blood samples were collected at rest and at the end of each stage of the test. Maximal fat oxidation rates decreased from 0.46 +/- 0.06 to 0.33 +/- 0.06 g min(-1) when carbohydrate was ingested before the start of exercise (P < 0.01). There was also a decrease in the intensity which elicited maximal fat oxidation (60.1 +/- 1.9% vs 52.0+3.4% VO2max) after carbohydrate ingestion (P < 0.05). Maximal power output was higher in the carbohydrate than in the placebo trial (346 +/- 12 vs 332 +/- 12 W) (P < 0.05). In conclusion, the ingestion of 75 g of carbohydrate 45 min before the onset of exercise decreased Fatmax by 14%, while the maximal rate of fat oxidation decreased by 28%.  相似文献   

5.
The aim of this study was to determine the effect of carbohydrate (CHO) versus placebo (PLA) beverage consumption on the immune and plasma cortisol responses to a soccer-specific exercise protocol in 8 university team soccer players. In a randomized, counterbalanced design, the players received carbohydrate or placebo beverages before, during and after two 90 min soccer-specific exercise bouts (3 days apart) designed to mimic the activities performed and the distance covered in a typical soccer match. Blood and saliva samples were collected before, during and after the exercise protocol. Plasma lactate concentration increased to approximately 4 mmol x l(-1) at 45 and 90 min of exercise in both treatments (P<0.01). Plasma glucose concentration was significantly lower after 90 min of exercise with ingestion of the placebo than the carbohydrate (PLA: 4.57+/-0.12 mmol x l(-1); CHO: 5.49+/-0.11 mmol x l(-1); P<0.01). The pattern of change in plasma cortisol, circulating lymphocyte count and saliva immunoglobulin A secretion did not differ between the carbohydrate and placebo trials. Blood neutrophil counts were 14% higher 1 h after the placebo trial than the carbohydrate trial (PLA: 4.8+/-0.5x10(9) cells x l(-1); CHO: 4.2+/-0.5x10(9) cells x l(-1); P = 0.06), but the treatment had no effect on the degranulation response of blood neutrophils stimulated by bacterial lipopolysaccharide. We conclude that, although previous studies have shown that carbohydrate feeding is effective in attenuating immune responses to prolonged continuous strenuous exercise, the same cannot be said for a soccer-specific intermittent exercise protocol. When overall exercise intensity is moderate, and changes in plasma glucose, cortisol and immune variables are relatively small, it would appear that carbohydrate ingestion has only a minimal influence on the immune response to exercise.  相似文献   

6.
The purpose of this study was to test the hypothesis that increased availability of blood-borne glucose would improve endurance after carbohydrate loading. A single-leg exercise model was employed, taking advantage of the fact that supercompensation of muscle glycogen occurs only in a previously exercised limb. Endurance time to exhaustion at 70% of maximal oxygen uptake (VO2 max) was determined for 11 males and three females who were then allocated to a control group or a high-carbohydrate (CHO) group. For 3 days following Test 1 the control group maintained a prescribed normal diet whilst the CHO group increased the proportion of energy derived from carbohydrate (62.1 +/- 4.3% cf. 43.9 +/- 2.0%, P less than 0.01). The endurance test was then repeated using the leg that was inactive during Test 1. Endurance time was increased on Test 2 (123.7 +/- 43.2 min cf. 98.5 +/- 21.9 min, P less than 0.05 one-tailed test) for the CHO group but not for the control group (101.8 +/- 21.7 min cf. 107.5 +/- 9.1 min, NS). There was no indication of enhanced carbohydrate metabolism during Test 2 for the CHO group but mean heart rate was lower during Test 2 than during Test 1 (145 +/- 14 beat min-1 cf. 152 +/- 12 beat min-1, P less than 0.05). These results suggest that the prior consumption of a high-carbohydrate diet improves endurance during high-intensity cycling with a limb with normal muscle glycogen concentration.  相似文献   

7.
In this study, we investigated the effect of ingesting carbohydrate alone or carbohydrate with protein on functional and metabolic markers of recovery from a rugby union-specific shuttle running protocol. On three occasions, at least one week apart in a counterbalanced order, nine experienced male rugby union forwards ingested placebo, carbohydrate (1.2 g · kg body mass(-1) · h(-1)) or carbohydrate with protein (0.4 g · kg body mass(-1) · h(-1)) before, during, and after a rugby union-specific protocol. Markers of muscle damage (creatine kinase: before, 258 ± 171 U · L(-1) vs. 24 h after, 574 ± 285 U · L(-1); myoglobin: pre, 50 ± 18 vs. immediately after, 210 ± 84 nmol · L(-1); P < 0.05) and muscle soreness (1, 2, and 3 [maximum soreness = 8] for before, immediately after, and 24 h after exercise, respectively) increased. Leg strength and repeated 6-s cycle sprint mean power were slightly reduced after exercise (93% and 95% of pre-exercise values, respectively; P < 0.05), but were almost fully recovered after 24 h (97% and 99% of pre-exercise values, respectively). There were no differences between trials for any measure. These results indicate that in experienced rugby players, the small degree of muscle damage and reduction in function induced by the exercise protocol were not attenuated by the ingestion of carbohydrate and protein.  相似文献   

8.
Nine male student games players consumed either flavoured water (0.1 g carbohydrate, Na+ 6 mmol x l(-1)), a solution containing 6.5% carbohydrate-electrolytes (6.5 g carbohydrate, Na+ 21 mmol x l(-1)) or a taste placebo (Na+ 2 mmol x l(-1)) during an intermittent shuttle test performed on three separate occasions at an ambient temperature of 30 degrees C (dry bulb). The test involved five 15-min sets of repeated cycles of walking and variable speed running, each separated by a 4-min rest (part A of the test), followed by 60 s run/60 s rest until exhaustion (part B of the test). The participants drank 6.5 ml x kg(-1) of fluid as a bolus just before exercise and thereafter 4.5 ml x kg(-1) during every exercise set and rest period (19 min). There was a trial order effect. The total distance completed by the participants was greater in trial 3 (8441 +/- 873 m) than in trial 1 (6839 +/- 512, P < 0.05). This represented a 19% improvement in exercise capacity. However, the trials were performed in a random counterbalanced order and the participants completed 8634 +/- 653 m, 7786 +/- 741 m and 7099 +/- 647 m in the flavoured water (FW), placebo (P) and carbohydrate-electrolyte (CE) trials, respectively (P = 0.08). Sprint performance was not different between the trials but was impaired over time (FW vs P vs CE: set 1, 2.41 +/- 0.02 vs 2.39 +/- 0.03 vs 2.39 +/- 0.03 s; end set, 2.46 +/- 0.03 vs 2.47 +/- 0.03 vs 2.47 +/- 0.02 s; main effect time, P < 0.01). The rate of rise in rectal temperature was greater in the carbohydrate-electrolyte trial (rise in rectal temperature/duration of trial, degrees C x h(-1); FW vs CE, P < 0.05; P vs CE, N.S.). Blood glucose concentrations were higher in the carbohydrate-electrolyte than in the other two trials (FW vs P vs CE:rest, 4.4 +/- 0.1 vs 4.3 +/- 0.1 vs 4.2 +/- 0.1 mmol x l(-1); end of exercise, 5.4 +/- 0.3 vs 6.4 +/- 0.6 vs 7.2 +/- 0.5 mmol x l(-1); main effect trial, P < 0.05; main effect time, P < 0.01). Plasma free fatty acid concentrations at the end of exercise were lower in the carbohydrate-electrolyte trial than in the other two trials (FW vs P vs CE: 0.57 +/- 0.08 vs 0.53 +/- 0.11 vs 0.29 +/- 0.04 mmol x l(-1); interaction, P < 0.01). The correlation between the rate of rise in rectal temperature (degrees C x h(-1)) and the distance completed was -0.91, -0.92 and -0.96 in the flavoured water, placebo and carbohydrate-electrolyte conditions, respectively (P < 0.01). Heart rate, blood pressure, plasma ammonia, blood lactate, plasma volume and rate of perceived exertion were not different between the three fluid trials. Although drinking the carbohydrate-electrolyte solution induced greater metabolic changes than the flavoured water and placebo solutions, it is unlikely that in these unacclimated males carbohydrate availability was a limiting factor in the performance of intermittent running in hot environmental conditions.  相似文献   

9.
The aim of this study was to determine the effect of carbohydrate (CHO) versus placebo (PLA) beverage consumption on the immune and plasma cortisol responses to a soccer-specific exercise protocol in 8 university team soccer players. In a randomized, counterbalanced design, the players received carbohydrate or placebo beverages before, during and after two 90min soccer-specific exercise bouts (3 days apart) designed to mimic the activities performed and the distance covered in a typical soccer match. Blood and saliva samples were collected before, during and after the exercise protocol. Plasma lactate concentration increased to ~4 mmol.l-1 at 45 and 90 min of exercise in both treatments (P? 0.01). Plasma glucose concentration was significantly lower after 90 min of exercise with ingestion of the placebo than the carbohydrate (PLA: 4.57 +/- 0.12 mmol.l-1; CHO: 5.49 +/- 0.11 mmol.l-1; P? 0.01). The pattern of change in plasma cortisol, circulating lymphocyte count and saliva immunoglobulin A secretion did not differ between the carbohydrate and placebo trials. Blood neutrophil counts were 14% higher 1 h after the placebo trial than the carbohydrate trial (PLA: 4.8 =/- 0.5 x 10 9 cells.l-1; CHO:4.2 +/- 0.5 x 10 9 cells.l-1; P=0.06),but the treatment had no effect on the degranulation response of blood neutrophils stimulated by bacterial lipopolysaccharide. We conclude that, although previous studies have shown that carbohydrate feeding is effective in attenuating immune responses to prolonged continuous strenuous exercise, the same cannot be said for a soccer-specific intermittent exercise protocol. When overall exercise intensity is moderate,and changes in plasma glucose, cortisol and immune variables are relatively small, it would appear that carbohydrate ingestion has only a minimal influence on the immune response to exercise.  相似文献   

10.
This study investigated the effect of a single session of resistance exercise on postprandial lipaemia. Eleven healthy normolipidaemic men with a mean age of 23 (standard error = 1.4) years performed two trials at least 1 week apart in a counterbalanced randomized design. In each trial, participants consumed a test meal (1.2 g fat, 1.1 g carbohydrate, 0.2 g protein and 68 kJ x kg(-1) body mass) between 08.00 and 09.00 h following a 12 h fast. The afternoon before one trial, the participants performed an 88 min bout of resistance exercise. Before the other trial, the participants were inactive (control trial). Resistance exercise was performed using free weights and included four sets of 10 repetitions of each of 11 exercises. Sets were performed at 80% of 10-repetition maximum with a 2 min work and rest interval. Venous blood samples were obtained in the fasted state and at intervals for 6 h postprandially. Fasting plasma triacylglycerol (TAG) concentration did not differ significantly between control (1.03 +/- 0.13 mmol x l(-1)) and exercise (0.94 +/- 0.09 mmol x l(-1)) trials (mean +/- standard error). Similarly, the 6 h total area under the plasma TAG concentration versus time curve did not differ significantly between the control (9.84 +/- 1.40 mmol l(-1) x 6 h(-1)) and exercise (9.38 +/- 1.12 mmol x l(-1) x 6 h(-1)) trials. These findings suggest that a single session of resistance exercise does not reduce postprandial lipaemia.  相似文献   

11.
Abstract

The aim of this study was to determine whether the ingestion of a carbohydrate-electrolyte solution would improve 1-h running performance in runners who had consumed a meal 3 h before exercise. Ten endurance-trained male runners completed two trials that required them to run as far as possible in 1 h on an automated treadmill that allowed changes in running speed without manual input. Following the consumption of the pre-exercise meal, which provided 2.5 g carbohydrate per kilogram body mass (BM), runners ingested either a 6.4% carbohydrate-electrolyte solution or placebo solution (i.e. 8 ml · kg BM?1) 30 min before and 2 ml · kg BM?1 at 15-min intervals throughout the 1-h run. There were no differences in total distance covered (placebo: 13,680 m, s = 1525; carbohydrate: 13,589 m, s = 1635) (P > 0.05). Blood glucose and lactate concentration, respiratory exchange ratio, and carbohydrate oxidation during exercise were not different between trials (P > 0.05). There were also no differences in ratings of perceived exertion, felt arousal or pleasure–displeasure between trials (P > 0.05). In conclusion, the ingestion of a 6.4% carbohydrate-electrolyte solution did not improve 1-h running performance when a high carbohydrate meal was consumed 3 h before exercise.  相似文献   

12.
A high ambient temperature reduces the capacity to perform prolonged exercise. Total carbohydrate oxidation is less, and thus glycogen depletion is not limiting. Fluid ingestion in the heat should, therefore, focus on maintenance of hydration status rather than on substrate provision. Six healthy males cycled to exhaustion at 60% of maximum oxygen consumption (VO2max) with no drink, ingestion of a 15% carbohydrate-electrolyte drink (1.45+/-0.29 litres) or ingestion of a 2% carbohydrate-electrolyte drink (3.12+/-0.47 litres). The ambient temperature was 30.2+/-0.6 degrees C (mean +/- s), with a relative humidity of 71+/-1% and an air speed of approximately 0.7 m x s(-1) on all trials. Weighted mean skin temperature, rectal temperature and heart rate were recorded and venous samples drawn for determination of plasma volume changes, blood metabolites, serum electrolytes and osmolality. Expired gas was collected to estimate rates of fuel oxidation. Exercise capacity was significantly (P < 0.05) different in all trials. The median (range) time to exhaustion was 70.9 min (39.4-97.4 min) in the no-drink trial, 84.0 min (62.7-145 min) in the 15% carbohydrate trial and 118 min (82.6-168 min) in the 2% carbohydrate trial. The 15% carbohydrate drink resulted in significantly (P < 0.05) elevated blood glucose and total carbohydrate oxidation compared with the no-drink trial. The 2% carbohydrate drink restored plasma volume to pre-exercise values by the end of exercise. No differences were observed in other thermoregulatory or cardiorespiratory responses between trials. These results suggest that fluid replacement with a large volume of a dilute carbohydrate drink is beneficial during exercise in the heat, but the precise mechanisms for the improved exercise capacity are unclear.  相似文献   

13.
The aim of this study was to assess the influence of ad libitum water ingestion, using a back-mounted hydration system (BMHS), on fluid balance during alpine skiing. Fourteen skiers skied on two different days. On one day, seven skiers ingested water during skiing via the BMHS and the other seven skiers refrained from fluid ingestion during skiing until the midday break (NW trial). On the second day, the trials were reversed. Results indicated that when skiers used the BMHS they drank significantly more water than during the NW trials (2.0 +/- 0.9 vs. 0.78 +/- 0.4 litres). However, skiers drank significantly more at the midday break during the NW trials than during the BMHS trials (0.78 +/- 0.4 vs. 0.4 +/- 0.2 litres). Percent change in plasma volume was less during the BMHS trials than during the NW trials (-0.1 +/- 5.3 vs. -4.9 +/- 5.2%), urine osmolality was maintained in the BMHS trials but rose from 295 +/- 80 to 818 +/- 168 mOsm . kg(-1) at midday during the NW trials, and body mass loss was minimized during the BMHS trials compared with the NW trials (0.4 +/- 0.4 vs. 1.1 +/- 0.2 kg). Skiers reported that they felt significantly better when they ingested water during the BMHS trials. In conclusion, a back-mounted hydration system allowed the skiers to maintain hydration status.  相似文献   

14.
Nine male triathletes were studied during 160 min of exercise at 65% VO2 max on two occasions to examine the effect of glucose polymer ingestion on energy and fluid balance. During one trial they received 200 ml of a 10% glucose polymer solution at 20 min intervals during exercise (CHO), while in the other they received an equal volume of a sweet placebo (CON). On average, blood glucose levels (CON = 4.2 +/- 0.2 mmol l-1, CHO = 4.8 +/- 0.1, mean +/- S.E.) and respiratory exchange ratios (CON = 0.84 +/- 0.01, CHO = 0.87 +/- 0.01) during exercise were higher (P less than 0.05) as a result of the glucose polymer ingestion. There were no differences between trials, however, in the estimated plasma volume changes during exercise. Exercise time to exhaustion at an intensity corresponding to 110% VO2 max, performed 5 min after the submaximal exercise, was not influenced by glucose polymer ingestion. Relative to a control exercise bout conducted without prior exercise, however, sprint performance and postexercise blood lactate accumulation were impaired in both trials. It is concluded that glucose polymer ingestion maintains blood glucose levels and a high rate of carbohydrate oxidation during prolonged exercise, without compromising fluid balance.  相似文献   

15.
补充糖和/或肌酸对赛后血清肌酸激酶活性的影响   总被引：2，自引：0，他引：2  
夏强  曹建民 《山东体育科技》2002,24(3):38-39,42
8名男性足球运动员，按正交表L4(23)进行实验设计，进行关于糖、肌酸补充对足球运动员血清肌酸激酶活性影响的效果观察实验。A组仅补充空白饮料；B组每天补充20克肌酸；C组每天仅补充100克以低聚糖为主的饮料；D组同时补充肌酸和低聚糖饮料，补充方法同B、C组。连续补充5天。补充前后进行血清肌酸激酶浓度的测试。补充前测试时均喝空白饮料，补充后测试时补充相应饮料。测试前进行模拟现场比赛。模拟现场比赛分为两个半场，各45分钟，间隔15分钟。每个半场包15个3分钟的循环，测量每个半场后的血清肌酸激酶的浓度。结果表明：单独补充糖或肌酸，同时补充糖和肌酸均可使运动员赛后的即刻血清肌酸激酶活性显著下降，而且糖和肌酸同时补充效果好。提示同时补充糖、肌酸有利于足球运动员提高赛场竞技能力。  相似文献   

16.
This study was designed to investigate the effect of ingesting a glucose plus fructose solution on the metabolic responses to soccer-specific exercise in the heat and the impact on subsequent exercise capacity. Eleven male soccer players performed a 90 min soccer-specific protocol on three occasions. Either 3 ml · kg(-1) body mass of a solution containing glucose (1 g · min(-1) glucose) (GLU), or glucose (0.66 g · min(-1)) plus fructose (0.33 g · min(-1)) (MIX) or placebo (PLA) was consumed every 15 minutes. Respiratory measures were undertaken at 15-min intervals, blood samples were drawn at rest, half-time and on completion of the protocol, and muscle glycogen concentration was assessed pre- and post-exercise. Following the soccer-specific protocol the Cunningham and Faulkner test was performed. No significant differences in post-exercise muscle glycogen concentration (PLA, 62.99 ± 8.39 mmol · kg wet weight(-1); GLU 68.62 ± 2.70; mmol · kg wet weight(-1) and MIX 76.63 ± 6.92 mmol · kg wet weight(-1)) or exercise capacity (PLA, 73.62 ± 8.61 s; GLU, 77.11 ± 7.17 s; MIX, 83.04 ± 9.65 s) were observed between treatments (P > 0.05). However, total carbohydrate oxidation was significantly increased during MIX compared with PLA (P < 0.05). These results suggest that when ingested in moderate amounts, the type of carbohydrate does not influence metabolism during soccer-specific intermittent exercise or affect performance capacity after exercise in the heat.  相似文献   

17.
Ingesting carbohydrate beverages during prolonged exercise is associated with fewer numbers of circulating neutrophils and attenuated neutrophil functional responses, yet there is little information about the effect of fluid intake alone on immune responses to prolonged exercise. The aim of this study was to examine the influence of regular fluid ingestion compared with no fluid ingestion on plasma cortisol, circulating neutrophil and lipopolysaccharide (LPS)-stimulated neutrophil degranulation responses to prolonged cycling. In a randomized design, nine recreationally active males cycled for 2 h at 65% VO2max on two occasions with either fluid ingestion (lemon-flavoured water, fluid trial) before and during the exercise, or with no fluid intake at all (no fluid trial). Venous blood samples were obtained at rest, immediately after exercise and 1 h after exercise. Immediately after exercise, the plasma cortisol concentration was significantly higher in the no fluid trial than in the fluid trial (592 +/- 62 vs 670 +/- 63 nmol x l(-1), P < 0.05). Circulating numbers of neutrophils increased 4.5-fold (P < 0.01) and LPS-stimulated elastase release per neutrophil decreased 34 +/- 7% (P < 0.01) immediately after exercise; there were no differences between trials. These results suggest that in ambient environmental conditions, fluid ingestion alone has a negligible effect on circulating neutrophil and LPS-stimulated neutrophil degranulation responses to prolonged exercise.  相似文献   

18.
A key goal of pre-exercise nutritional strategies is to maximize carbohydrate stores, thereby minimizing the ergolytic effects of carbohydrate depletion. Increased dietary carbohydrate intake in the days before competition increases muscle glycogen levels and enhances exercise performance in endurance events lasting 90 min or more. Ingestion of carbohydrate 3-4 h before exercise increases liver and muscle glycogen and enhances subsequent endurance exercise performance. The effects of carbohydrate ingestion on blood glucose and free fatty acid concentrations and carbohydrate oxidation during exercise persist for at least 6 h. Although an increase in plasma insulin following carbohydrate ingestion in the hour before exercise inhibits lipolysis and liver glucose output, and can lead to transient hypoglycaemia during subsequent exercise in susceptible individuals, there is no convincing evidence that this is always associated with impaired exercise performance. However, individual experience should inform individual practice. Interventions to increase fat availability before exercise have been shown to reduce carbohydrate utilization during exercise, but do not appear to have ergogenic benefits.  相似文献   

19.
There is little published data in relation to the effects of caffeine upon cycling performance, speed and power in trained cyclists, especially during cycling of approximately 60 s duration. To address this, eight trained cyclists performed a 1 km time-trial on an electronically braked cycle ergometer under three conditions: after ingestion of 5 mg x kg-1 caffeine, after ingestion of a placebo, or a control condition. The three time-trials were performed in a randomized order and performance time, mean speed, mean power and peak power were determined. Caffeine ingestion resulted in improved performance time (caffeine vs. placebo vs. control: 71.1 +/- 2.0 vs. 73.4 +/- 2.3 vs. 73.3 +/- 2.7 s; P = 0.02; mean +/- s). This change represented a 3.1% (95% confidence interval: 0.7-5.6) improvement compared with the placebo condition. Mean speed was also higher in the caffeine than placebo and control conditions (caffeine vs. placebo vs. control: 50.7 +/- 1.4 vs. 49.1 +/- 1.5 vs. 49.2 +/- 1.7 km x h-1; P = 0.0005). Mean power increased after caffeine ingestion (caffeine vs. placebo vs. control: 523 +/- 43 vs. 505 +/- 46 vs. 504 +/- 38 W; P = 0.007). Peak power also increased from 864 +/- 107 W (placebo) and 830 +/- 87 W (control) to 940 +/- 83 W after caffeine ingestion (P = 0.027). These results provide support for previous research that found improved performance after caffeine ingestion during short-duration high-intensity exercise. The magnitude of the improvements observed in our study could be due to our use of sport-specific ergometry, a tablet form and trained participants.  相似文献   

20.
Carbohydrate ingestion before and during endurance exercise delays the onset of fatigue (reduced power output). Therefore, endurance athletes are recommended to ingest diets high in carbohydrate (70% of total energy) during competition and training. However, increasing the availability of plasma free fatty acids has been shown to slow the rate of muscle and liver glycogen depletion by promoting the utilization of fat. Ingested fat, in the form of long-chain (C 16-22 ) triacylglycerols, is largely unavailable during acute exercise, but medium-chain (C 8-10 ) triacylglycerols are rapidly absorbed and oxidized. We have shown that the ingestion of medium-chain triacylglycerols in combination with carbohydrate spares muscle carbohydrate stores during 2 h of submaximal (< 70% VO 2 peak) cycling exercise, and improves 40 km time-trial performance. These data suggest that by combining carbohydrate and medium-chain triacylglycerols as a pre-exercise supplement and as a nutritional supplement during exercise, fat oxidation will be enhanced, and endogenous carbohydrate will be spared. We have also examined the chronic metabolic adaptations and effects on substrate utilization and endurance performance when athletes ingest a diet that is high in fat (> 70% by energy). Dietary fat adaptation for a period of at least 2-4 weeks has resulted in a nearly two-fold increase in resistance to fatigue during prolonged, low- to moderate-intensity cycling (< 70% VO 2 peak). Moreover, preliminary studies suggest that mean cycling 20 km time-trial performance following prolonged submaximal exercise is enhanced by 80 s after dietary fat adaptation and 3 days of carbohydrate loading. Thus the relative contribution of fuel substrate to prolonged endurance activity may be modified by training, pre-exercise feeding, habitual diet, or by artificially altering the hormonal milieu or the availability of circulating fuels. The time course and dose-response of these effects on maximizing the oxidative contribution of fat for exercise metabolism and in exercise performance have not been systematically studied during moderate- to high-intensity exercise in humans.  相似文献   

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