Increased dietary carbohydrate and endurance during single‐leg cycling using a limb with normal muscle glycogen concentration

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 (VO₂max) 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 < 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 <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<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.     

Skeletal muscle glycogen concentration and metabolic responses following a high glycaemic carbohydrate breakfast

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 x 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 x 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 x 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 x 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.     

Influence of single-leg training on muscle metabolism and endurance during exercise with the trained limb and the untrained limb

We have previously shown that single-leg training results in improved endurance for exercise with the untrained leg (UTL) as well as for exercise with the trained leg (TL). The purpose of this study was to see whether the improved endurance of the untrained leg could be explained on the basis of changes in muscle metabolism. Exercise time to exhaustion at 80% of maximum oxygen uptake (VO2 max) was determined for each leg separately, pre- and post-training. Muscle metabolite concentrations were measured pre- and post-training in biopsy samples obtained immediately before this endurance test and at the pre-training point of exhaustion (END1). After six weeks of single-leg training endurance time was increased for both the UTL and the TL (UTL 34.0 +/- 16.4 min vs 97.9 +/- 26.3 min, P less than 0.01; TL 28.3 +/- 10.1 min vs 169.0 +/- 32.6 min, P less than 0.01). No changes in muscle metabolite concentrations were found in resting muscle. Training increased muscle ATP (P less than 0.05) and glycogen (P less than 0.01) concentrations and decreased muscle lactate concentration (P less than 0.05) in the TL at END1. No significant changes in muscle metabolite concentrations were found for the UTL. The improved endurance of the contralateral limb after single-leg training could not be explained on the basis of changes in muscle metabolism.     

Gross efficiency responses to exercise conditioning in adult males of various ages.

This study investigated gross efficiency changes in a group of 60 adult males (mean age 39.2 +/- 1.2 years) resulting from endurance training and age-related responses to such training in sub-groups (each n = 20) of younger (30.7 +/- 0.7 years), intermediate (38.3 +/- 0.5 years) and older (48.6 +/- 1.1 years) subjects. Gross efficiency (%) was calculated from work output, oxygen consumption and RER energy equivalents following 10 min standard cycle ergometry exercise at 100 W and 50 rev min-1. Measurements were made at pre-, mid- and post-8 months of training, which involved progressive walking/jogging activities designed to enhance endurance capacity. In the total group, VO2 decreased pre- to post-training from 2.15 +/- 0.02 to 1.93 +/- 0.01 1 min-1 (P less than 0.01). In the sub-groups, both the younger and older subjects showed a significantly reduced VO2, from 2.17 +/- 0.01 to 1.98 +/- 0.04 1 min-1 and 2.05 +/- 0.08 to 1.86 +/- 0.03 1 min-1 respectively (P less than 0.05), but no significant changes were noted at mid-training. In the intermediate age subjects, while there were trends towards a reduced VO2, none was significant. The ANOVA revealed increased mean gross efficiency in the total group from pre- (14.3 +/- 0.1%) to post- (15.5 +/- 0.2%) (P less than 0.05) but not at mid-training (14.8 +/- 0.2%). While similar trends were observed in the sub-groups, gross efficiency increases were not significant, although changes in gross efficiency were reflected in VO2. The findings suggest that during standardized exercise, oxygen cost may be reduced and gross efficiency increased in adult males following endurance training and that such changes may take place over a variety of age ranges.     

Endurance running performance in athletes with asthma

Laboratory assessment was made during maximal and submaximal exercise on 16 endurance trained male runners with asthma (aged 35 +/- 9 years) (mean +/- S.D.). Eleven of these asthmatic athletes had recent performance times over a half-marathon, which were examined in light of the results from the laboratory tests. The maximum oxygen uptake (VO2max) of the group was 61.8 +/- 6.3 ml kg-1 min-1 and the maximum ventilation (VEmax) was 138.7 +/- 24.7 l min-1. These maximum cardio-respiratory responses to exercise were positively correlated to the degree of airflow obstruction, defined as the forced expiratory volume in 1 s (expressed as a percentage of predicted normal). The half-marathon performance times of 11 of the athletes ranged from those of recreational to elite runners (82.4 +/- 8.8 min, range 69-94). Race pace was correlated with VO2max (r = 0.863, P less than 0.01) but the highest correlation was with the running velocity at a blood lactate concentration of 2 mmol l-1 (r = 0.971, P less than 0.01). The asthmatic athletes utilized 82 +/- 4% VO2max during the half-marathon, which was correlated with the %VO2max at 2 mmol l-1 blood lactate (r = 0.817, P less than 0.01). The results of this study suggest that athletes with mild to moderate asthma can possess high VO2max values and can develop a high degree of endurance fitness, as defined by their ability to sustain a high percentage of VO2max over an endurance race. In athletes with more severe airflow obstruction, the maximum ventilation rate may be reduced and so VO2max may be impaired. The athletes in the present study have adapted to this limitation by being able to sustain a higher %VO2max before the accumulation of blood lactate, which is an advantage during an endurance race. Therefore, with appropriate training and medication, asthmatics can successfully participate in endurance running at a competitive level.     

Effect of glucose polymer ingestion on energy and fluid balance during exercise

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.     

The effects of carbohydrate supplementation on immune responses to a soccer-specific exercise protocol

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.     

An anthropometric analysis of elite Australian track cyclists

An anthropometric analysis was conducted on 35 elite male Australian track cyclists having a mean age of 22.6 years and who had been competing on average for 9 years. The relationship of anthropometric parameters to both bicycle saddle height and cycling performance was also investigated. Subjects were allocated, for purposes of comparison, to an endurance or sprint group on the basis of their competitive event. The group members in total were ectomorphic mesomorphs of height 178 +/- 4.8 cm and weight 72.5 +/- 6.6 kg on average. Percentage of saddle height to lower limb length averaged 99 +/- 1.6%, and significant correlations existed between strength and both body mass (r = 0.57) and thigh girth (r = 0.55). No significant correlation was seen between any anthropometric parameter and performance in an individual event. Cyclists in the spint group were heavier (76.2 +/- 7.4 vs. 70.0 +/- 4.7 kg, P less than 0.01) and stronger (258 +/- 44.4 vs. 216 +/- 30.5 Nm, P less than 0.01), and had larger chest (98.2 +/- 6.2 vs. 92.4 +/- 2.9 cm, P less than 0.01), arm (33.0 +/- 2.2 vs. 30.7 +/- 1.6 cm, P less than 0.01), thigh (57.5 +/- 3.4 vs. 54.3 +/- 2.5 cm, P less than 0.01) and calf girths (37.8 +/- 1.7 vs. 36.2 +/- 1.9 cm, P less than 0.05) than cyclists in the endurance group. They were also more mesomorphic (5.3 +/- 0.7 vs. 4.7 +/- 0.8, P less than 0.05) and less ectomorphic (2.3 +/- 0.9 vs. 2.9 +/- 0.6, P less than 0.05) than the endurance cyclists.     

The effects of carbohydrate supplementation on immune responses to a soccer-specific exercise protocol

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.     

Skeletal muscle glycogen concentration and metabolic responses following a high glycaemic carbohydrate breakfast

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.     

The effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment

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.     

Nutrition for endurance sports: marathon, triathlon, and road cycling

Endurance sports are increasing in popularity and athletes at all levels are looking for ways to optimize their performance by training and nutrition. For endurance exercise lasting 30 min or more, the most likely contributors to fatigue are dehydration and carbohydrate depletion, whereas gastrointestinal problems, hyperthermia, and hyponatraemia can reduce endurance exercise performance and are potentially health threatening, especially in longer events (>4 h). Although high muscle glycogen concentrations at the start may be beneficial for endurance exercise, this does not necessarily have to be achieved by the traditional supercompensation protocol. An individualized nutritional strategy can be developed that aims to deliver carbohydrate to the working muscle at a rate that is dependent on the absolute exercise intensity as well as the duration of the event. Endurance athletes should attempt to minimize dehydration and limit body mass losses through sweating to 2-3% of body mass. Gastrointestinal problems occur frequently, especially in long-distance races. Problems seem to be highly individual and perhaps genetically determined but may also be related to the intake of highly concentrated carbohydrate solutions, hyperosmotic drinks, as well as the intake of fibre, fat, and protein. Hyponatraemia has occasionally been reported, especially among slower competitors with very high intakes of water or other low sodium drinks. Here I provide a comprehensive overview of recent research findings and suggest several new guidelines for the endurance athlete on the basis of this. These guidelines are more detailed and allow a more individualized approach.     

Assessment of the power performance of racing cyclists

A 30-s 'all-out' power protocol was studied in four groups of racing cyclists including internationals (n = 8), Category 1 (n = 10), Category 2 (n = 15) and Category 3 (n = 11). Following warm-up each subject completed five trials interspersed by 3 min of low intensity exercise on an ergowheel racing cycle ergometry system at a power output of 15 W kg-1 body weight, generated at 130 rev min-1. Temporal indices of performance included delay time (DT) to achieve the power criterion, total time (TT) of the maintenance of the power criterion and the ratio of TT/DT. 'Explosive' leg strength was assessed from a vertical jump. The results indicated that international and Category 1 cyclists had lower DT (2.2 +/- 0.1 s and 2.1 +/- 0.0 s, respectively; P less than 0.05), higher TT (28.1 +/- 0.7 s and 27.0 +/- 0.7 s, respectively; P less than 0.05) and elevated TT/DT (12.8 and 12.9, respectively; P less than 0.01). 'Explosive' leg strength was also higher (P less than 0.05) in the internationals than in the other groups of cyclists. The protocol provides a sport-related method for the assessment of short term endurance performance ability in racing cyclists which may be of value in identifying the anaerobic capability of individual cyclists.     

Influence of ingesting a carbohydrate‐electrolyte solution on endurance capacity during intermittent,high‐intensity shuttle running

The aim of this study was to examine the effects of ingesting a carbohydrate‐electrolyte solution on endurance capacity during a prolonged intermittent, high‐intensity shuttle running test (PIHSRT). Nine trained male games players performed two exercise trials, 7 days apart. On each occasion, they completed 75 min exercise, comprising of five 15‐min periods of intermittent running, consisting of sprinting, interspersed with periods of jogging and walking (Part A), followed by intermittent running to fatigue (Part B). The subjects were randomly allocated either a 6.9% carbohydrate‐electrolyte solution (CHO) or a non‐carbohydrate placebo (CON) immediately prior to exercise (5 ml kg^‐1 body mass) and every 15 min thereafter (2 ml kg^‐1 body mass). Venous blood samples were obtained at rest, during and after each PIHSRT for the determination of glucose, lactate, plasma free fatty acid, glycerol, ammonia, and serum insulin and electrolyte concentrations. During Part B, the subjects were able to continue running longer when fed CHO (CHO = 8.9 ± 1.5 min vs CON = 6.7 ± 1.0 min; P < 0.05) (mean ± s.e.m.). These results show that drinking a carbohydrate‐electrolyte solution improves endurance running capacity during prolonged intermittent exercise.     

Pre-exercise carbohydrate and fat ingestion: effects on metabolism and performance

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.     

Post-exercise ingestion of different amounts of protein affects plasma insulin concentration in humans

Abstract

The synergistic stimulating effect of combined intake of carbohydrate and protein on plasma insulin concentration has been reported previously. However, it remains unclear whether the amount of protein ingested after exercise affects the concentrations of plasma insulin and amino acids. This study of trained men compared the effects of post-exercise co-ingestion of carbohydrate plus different amounts of whey protein hydrolysates (WPHs) with carbohydrate alone on (1) blood biochemical parameters of carbohydrate metabolism during the post-exercise phase, and (2) endurance performance. Eight trained men exercised continuously for 70 min. Immediately after exercise and 30, 60, 90, and 120 min later, the participants received supplements containing: (1) 17.5 g carbohydrate, (2) 3.0 g WPHs and 17.5 g carbohydrate (L-WPH), or (3) 8.0 g WPHs and 17.5 g carbohydrate (H-WPH). After a 2-h recovery period, the participants performed an endurance performance test. The concentrations of blood glucose were lower and plasma insulin significantly higher in the H-WPH trial compared with the carbohydrate trial. The concentrations of plasma amino acids were increased in a dose-dependent manner following ingestion of different amounts of WPHs with carbohydrate. Endurance performance was not significantly different between the three trials. Co-ingestion of carbohydrate and H-WPH was more effective than ingestion of carbohydrate alone for stimulating insulin secretion and increasing the availability of plasma amino acids. These results suggest that plasma concentrations of amino acids during the recovery period are determined by the amount of dietary protein ingested, and that it is necessary to increase the concentration of plasma amino acids above a certain level to stimulate insulin secretion.     

An exercise protocol that simulates the activity patterns of elite junior squash

Squash is a popular racket sport that requires intermittent activity with frequent bursts of near maximal-intensity exercise. Consequently, effective physiological and thermoregulatory responses are important contributors to performance during squash match-play. Controlled field-based simulation protocols have been introduced in a growing number of sports, which allow sports scientists to investigate changes in physiology and the efficacy of various interventions in sport-specific contexts. This study aimed to develop an exercise protocol that simulates the physiological requirements of elite squash match-play. Eight elite junior squash players (age 16.2+/-0.8 years, height 1.76+/-0.06 m, body mass 61.3+/-5.9 kg; mean+/-s) completed the following in a randomized order: (1) a squash match against a player of similar standard and (2) a squash-specific incremental exercise protocol (multistage squash test [MST]) followed by the squash simulation protocol (SSP). The multistage squash test was continued for 18.0+/-1.0 min and elicited near maximal post-MST heart rates, blood lactate concentrations and ratings of perceived exertion (198+/-9 beats.min-1, 5.7+/-1.7 mmol.l-1 and 18+/-1, respectively). The SSP was 12.2 min in length compared with mean game length during competitive matches of 10.0+/-1.6 min (P=0.27). Peak heart rates were similar during the SSP and match-play (192+/-11 and 189+/-6 beats.min-1, respectively; P=0.44). Mean exercising heart rates were similar during the SSP (180+/-8 beats.min-1) and match-play (179+/-13 beats.min-1; P=0.73). Peak blood lactate concentrations during the SSP and match-play were 3.5+/-1.5 and 2.4+/-1.2 mmol.l-1 (P=0.07), respectively. Peak ratings of perceived exertion during the SSP and match-play were similar (17+/-2 and 17+/-2, respectively; P=0.64). It was concluded that the SSP closely replicated the demands of squash match-play in elite junior squash players. Furthermore, the SSP provides coaches and scientific support staff with a controlled squash-specific exercise protocol that has potential application in the objective investigation of a range of interventions such as training programmes, nutritional supplements and strategies to maintain core body temperature.     

Urea production during prolonged swimming

Male interscholastic swimmers (n = 8) completed a 4572 m training swim in in 62 +/- 1.1 min (means +/- S.E.) with terminal heart rate and blood lactate of 152 +/- 6 beats min-1 and 6.9 +/- 0.89 mM, respectively. Sweat rate (0.48 +/- 0.095 l. h-1) was lower than similar intensity cycling (1.5 +/- 0.13 l. h-1) or running (1.1 +/- 0.14 l. h-1). Post-swim serum urea N (11.6 +/- 0.71 mM) was elevated (P less than 0.05) vs pre-swim (4.6 +/- 0.39 mM). Post-swim urine volume (860 +/- 75 ml 24 h-1) was reduced (P less than 0.07) and resulted in an elevated (P less than 0.05), but delayed (24-84 h), post-exercise urea N excretion. Although the reduced urine and sweat production during the swim undoubtedly contributed to the elevated serum urea, there must be another explanation because together they could only account for 38% of the observed increase. On the basis of the magnitude of serum urea increase, it appears that the swim caused an increase in urea production (amino acid oxidation). The failure to observe larger increases in urinary urea during recovery indicates that either urea excretion following exercise continues for prolonged periods of time (greater than 48 h) or another significant mode of nitrogen excretion exists.     

补充糖对运动员训练和竞技能力的影响

运动员饮食中含糖低于“最适宜的”量易诱发过早疲劳。在进行长时间运动时疲劳常因肌糖元排空,其含量低于临界值(50mM/kg湿肌)或血糖浓度降至临界值(3.3mM/L)以下引起,这时运动强度必将显著降低甚或被中止。因此,摄食高糖饮食可增加肌糖元及改善耐力,维持高的训练质量。摄食糖的数量、糖的类型和摄取时间三者都是改善运动后恢复速率的营养策略的组成部分。     

The effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment

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 (VO 2max ) 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°C (mean - s ), with a relative humidity of 71 - 1% and an air speed of approximately 0.7 m.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.