Effects of carbohydrate and chromium ingestion during intermittent high-intensity exercise to fatigue

Meta-Analysis of Carbohydrate Solution Intake during Prolonged Exercise in Adults: From the Last 45+ Years' Perspective

Carbohydrate (CHO) supplementation during prolonged exercise postpones fatigue. However, the optimum administration timing, dosage, type of CHO intake, and possible interaction of the ergogenic effect with athletes' cardiorespiratory fitness (CRF) are not clear. Ninety-six studies (from relevant databases based on predefined eligibility criteria) were selected for meta-analysis to investigate the acute effect of ≤20% CHO solutions on prolonged exercise performance. The between-subject standardized mean difference [SMD = ([mean post-value treatment group-mean post-value control group]/pooled variance)] was assessed. Overall, SMD [95% CI] of 0.43 [0.35, 0.51] was significant (p < 0.001). Subgroup analysis showed that SMD was reduced as the subjects' CRF level increased, with a 6-8% CHO solution composed of GL:FRU improving performance (exercise: 1-4 h); administration during the event led to a superior performance compared to administration before the exercise, with a 6-8% single-source CHO solution increasing performance in intermittent and 'stop and start' sports and an ~6% CHO solution appearing beneficial for 45-60 min exercises, but there were no significant differences between subjects' gender and age groups, varied CHO concentrations, doses, or types in the effect measurement. The evidence found was sound enough to support the hypothesis that CHO solutions, when ingested during endurance exercise, have ergogenic action and a possible crossover interaction with the subject's CRF.

The Comparison of the Effects between Continuous and Intermittent Energy Restriction in Short-Term Bodyweight Loss for Sedentary Population: A Randomized, Double-Blind, Controlled Trial

Objective: To compare the effects of continuous energy restriction (CER) and intermittent energy restriction (IER) in bodyweight loss plan in sedentary individuals with normal bodyweight and explore the influence factors of effect and individual retention. Methods: 26 participants were recruited in this randomized controlled and double-blinded trial and allocated to CER and IER groups. Bodyweight (BW), body mass index (BMI), and resting metabolic rate (RMR) would be collected before and after a 4-week (28 days) plan which included energy restriction (CER or IER) and moderate-intensity exercise. Daily intake of three major nutrients (protein, carbohydrate, fat) and calories were recorded. Results: A significant decrease in BW and BMI were reported within each group. No statistically significant difference in the change of RMR in CERG. No statistically significant difference was reported in the effect between groups, neither as well the intake of total calories, three major nutrients, and individual plan retention. The influence factors of IER and CER are different. Conclusion: Both CER and IER are effective and safe energy restriction strategies in the short term. Daily energy intake and physical exercise are important to both IER and CER.

Carbohydrate Drink Use During 30 Minutes of Variable-Intensity Exercise Has No Effect on Exercise Performance in Premenarchal Girls

PURPOSE

This study examined the physiological, perceptual, and performance effects of a 6% carbohydrate (CHO) drink during variable-intensity exercise (VIE) and a postexercise test in premenarchal girls.

METHODS

A total of 10 girls (10.4 [0.7] y) participated in the study. VO2peak was assessed, and the girls were familiarized with VIE and performance during the first visit. The trial order (CHO and placebo) was randomly assigned for subsequent visits. The drinks were given before VIE bouts and 1-minute performance (9 mL/kg total). Two 15-minute bouts of VIE were completed (10 repeated sequences of 20%, 55%, and 95% power at VO2peak and maximal sprints) before a 1-minute performance sprint.

RESULTS

The mean power, peak power, heart rate (HR), %HRpeak, and rating of perceived exertion during VIE did not differ between trials. However, the peak power decreased, and the rating of perceived exertion increased from the first to the second bout. During the 1-minute performance, there were no differences between the trial (CHO vs placebo) for HR (190 [9] vs 189 [9] bpm), %HRpeak (97.0% [3.2%] vs 96.6% [3.0%]), rating of perceived exertion (7.8 [2.3] vs 8.1 [1.9]), peak power (238 [70] vs 235 [60] W), fatigue index (54.7% [10.0%] vs 55.9% [12.8%]), or total work (9.4 [2.6] vs 9.4 [2.1] kJ).

CONCLUSION

CHO supplementation did not alter physiological, perceptual, or performance responses during 30 minutes of VIE or postexercise sprint performance in premenarchal girls.

Energy Balance Coexists With Disproportionate Macronutrient Consumption Across Pretraining, During Training, and Posttraining Among Indian Junior Soccer Players

PURPOSE

To evaluate energy expenditure, energy intake, and nutrient adequacy of Indian junior soccer players.

METHOD

Forty junior national-level soccer players (Under-12 and Under-16 age groups) were assessed for 3-day weighed food records and 3-day energy expenditure. Energy and nutrient intake was analyzed from food records, and energy expenditure was measured using a portable metabolic analyzer and activity records. Nutrient adequacy was determined by comparing intake with prevailing recommendations.

RESULTS

Players exhibited no significant difference between energy intake (boys = 3062 [340.9] and girls = 2243 [320.3] kcal·d^-1) and expenditure (boys = 2875 [717.3] and girls = 2442 [350.3] kcal·d^-1). Across age groups, the Under-12 boys showed positive energy balance as against energy deficits in Under-16. Girls showed energy deficits, although not significant. There were 58% of girls showing energy availability <30 kcal·kg^-1 fat-free mass, of which 37% were Under-16 players. Carbohydrates contributed to >60% of energy expenditure among 95.2% boys and 73.7% girls. Among 52.4% boys and 47.4% girls, <25% of energy expenditure was contributed by fat. More than 95% players consumed <1 g·kg^-1 carbohydrates pretraining and 100% of them consumed >1.2 g·kg^-1 carbohydrates posttraining.

CONCLUSION

Junior soccer players consumed more than recommended carbohydrates in the diet, although not aligning with the pretraining, during training, and posttraining meal requirements. Considering the energy deficits observed among Under-16 players, a suitable dietary modification is warranted.

Ecologically Valid Carbohydrate Intake during Soccer-Specific Exercise Does Not Affect Running Performance in a Fed State

This study assessed the effect of carbohydrate intake on self-selected soccer-specific running performance. Sixteen male soccer players (age 23 ± 4 years; body mass 76.9 ± 7.2 kg; predicted VO_2max = 54.2 ± 2.9 mL∙kg⁻¹∙min⁻¹; soccer experience 13 ± 4 years) completed a progressive multistage fitness test, familiarisation trial and two experimental trials, involving a modified version of the Loughborough Intermittent Shuttle Test (LIST) to simulate a soccer match in a fed state. Subjects completed six 15 min blocks (two halves of 45 min) of intermittent shuttle running, with a 15-min half-time. Blocks 3 and 6, allowed self-selection of running speeds and sprint times, were assessed throughout. Subjects consumed 250 mL of either a 12% carbohydrate solution (CHO) or a non-caloric taste matched placebo (PLA) before and at half-time of the LIST. Sprint times were not different between trials (CHO 2.71 ± 0.15 s, PLA 2.70 ± 0.14 s; p = 0.202). Total distance covered in self-selected blocks (block 3: CHO 2.07 ± 0.06 km; PLA 2.09 ± 0.08 km; block 6: CHO 2.04 ± 0.09 km; PLA 2.06 ± 0.08 km; p = 0.122) was not different between trials. There was no difference between trials for distance covered (p ≥ 0.297) or mean speed (p ≥ 0.172) for jogging or cruising. Blood glucose concentration was greater (p < 0.001) at the end of half-time during the CHO trial. In conclusion, consumption of 250 mL of 12% CHO solution before and at half-time of a simulated soccer match does not affect self-selected running or sprint performance in a fed state.

Carbohydrate Nutrition and Team Sport Performance

The common pattern of play in 'team sports' is 'stop and go', i.e. where players perform repeated bouts of brief high-intensity exercise punctuated by lower intensity activity. Sprints are generally 2-4 s long and recovery between sprints is of variable length. Energy production during brief sprints is derived from the degradation of intra-muscular phosphocreatine and glycogen (anaerobic metabolism). Prolonged periods of multiple sprints drain muscle glycogen stores, leading to a decrease in power output and a reduction in general work rate during training and competition. The impact of dietary carbohydrate interventions on team sport performance have been typically assessed using intermittent variable-speed shuttle running over a distance of 20 m. This method has evolved to include specific work to rest ratios and skills specific to team sports such as soccer, rugby and basketball. Increasing liver and muscle carbohydrate stores before sports helps delay the onset of fatigue during prolonged intermittent variable-speed running. Carbohydrate intake during exercise, typically ingested as carbohydrate-electrolyte solutions, is also associated with improved performance. The mechanisms responsible are likely to be the availability of carbohydrate as a substrate for central and peripheral functions. Variable-speed running in hot environments is limited by the degree of hyperthermia before muscle glycogen availability becomes a significant contributor to the onset of fatigue. Finally, ingesting carbohydrate immediately after training and competition will rapidly recover liver and muscle glycogen stores.

Acute Effects of Carbohydrate Supplementation on Intermittent Sports Performance

Intermittent sports (e.g., team sports) are diverse in their rules and regulations but similar in the pattern of play; that is, intermittent high-intensity movements and the execution of sport-specific skills over a prolonged period of time (~1–2 h). Performance during intermittent sports is dependent upon a combination of anaerobic and aerobic energy systems, both of which rely on muscle glycogen and/or blood glucose as an important substrate for energy production. The aims of this paper are to review: (1) potential biological mechanisms by which carbohydrate may impact intermittent sport performance; (2) the acute effects of carbohydrate ingestion on intermittent sport performance, including intermittent high-intensity exercise capacity, sprinting, jumping, skill, change of direction speed, and cognition; and (3) what recommendations can be derived for carbohydrate intake before/during exercise in intermittent sports based on the available evidence. The most researched intermittent sport is soccer but some sport-specific studies have also been conducted in other sports (e.g., rugby, field hockey, basketball, American football, and racquet sports). Carbohydrate ingestion before/during exercise has been shown in most studies to enhance intermittent high-intensity exercise capacity. However, studies have shown mixed results with regards to the acute effects of carbohydrate intake on sprinting, jumping, skill, change of direction speed, and cognition. In most of these studies the amount of carbohydrate consumed was ~30–60 g/h in the form of a 6%–7% carbohydrate solution comprised of sucrose, glucose, and/or maltodextrin. The magnitude of the impact that carbohydrate ingestion has on intermittent sport performance is likely dependent on the carbohydrate status of the individual; that is, carbohydrate ingestion has the greatest impact on performance under circumstances eliciting fatigue and/or hypoglycemia. Accordingly, carbohydrate ingestion before and during a game seems to have the greatest impact on intermittent sports performance towards the end of the game.

The effect of carbohydrate ingestion on performance during a simulated soccer match

Aim: This study investigated how performance was affected after soccer players, in a postprandial state, ingested a 7% carbohydrate (CHO) solution compared to a placebo (0% CHO) during a simulated soccer match. Methods: Using a double-blind placebo-controlled design, 22 trained male league soccer players (age: 24 ± 7 years, wt: 73.4 ± 12.0 kg, VO₂max: 51.8 ± 4.3 mL O₂/kg/min) completed two trials, separated by 7 days, during which they ingested, in random order, 700 mL of either a 7% CHO or placebo drink during a simulated soccer match. Ratings of perceived exertion (RPE), agility, timed and run to fatigue were measured during the trials. Results: Change in agility times was not altered by CHO vs. placebo ingestion (0.57 ± 1.48 vs. 0.66 ± 1.00, p = 0.81). Timed runs to fatigue were 381 ± 267 s vs. 294 ± 159 s for the CHO and placebo drinks, respectively (p = 0.11). Body mass modified the relationship between time to fatigue and drink ingestion (p = 0.02 for drink × body mass), such that lower body mass was associated with increased time to fatigue when the players ingested CHO, but not placebo. RPE values for the final stage of the simulated soccer match were 8.5 ± 1.7 and 8.6 ± 1.5 for the CHO and placebo drinks respectively (p = 0.87). Conclusions: The group data showed that the 7% CHO solution (49 g CHO) did not significantly improve performance during a simulated soccer match in league soccer players who had normal pre-match nutrition. However, when adjusting for body mass, increasing CHO intake was associated with improved time to fatigue during the simulated soccer match.

Carbohydrate supplementation and prolonged intermittent high-intensity exercise in adolescents: research findings, ethical issues and suggestions for the future

In the last decade, research has begun to investigate the efficacy of carbohydrate supplementation for improving aspects of physical capacity and skill performance during sport-specific exercise in adolescent team games players. This research remains in its infancy, and further study would be beneficial considering the large youth population actively involved in team games. Literature on the influence of carbohydrate supplementation on skill performance is scarce, limited to shooting accuracy in adolescent basketball players and conflicting in its findings. Between-study differences in the exercise protocol, volume of fluid and carbohydrate consumed, use of prior fatiguing exercise and timing of skill tests may contribute to the different findings. Conversely, initial data supports carbohydrate supplementation in solution and gel form for improving intermittent endurance running capacity following soccer-specific shuttle running. These studies produced reliable data, but were subject to limitations including lack of quantification of the metabolic response of participants, limited generalization of data due to narrow participant age and maturation ranges, use of males and females within the same sample and non-standardized pre-exercise nutritional status between participants. There is a lack of consensus regarding the influence of frequently consuming carbohydrate-containing products on tooth enamel erosion and the development of obesity or being overweight in adolescent athletes and non-athletes. These discrepancies mean that the initiation or exacerbation of health issues due to frequent consumption of carbohydrate-containing products by adolescents cannot be conclusively refuted. Coupled with the knowledge that consuming a natural, high-carbohydrate diet -3-8 hours before exercise can significantly alter substrate use and improve exercise performance in adults, a moral and ethical concern is raised regarding the direction of future research in order to further knowledge while safeguarding the health and well-being of young participants. It could be deemed unethical to continue study into carbohydrate supplementation while ignoring the potential health concerns and the possibility of generating similar performance enhancements using natural dietary interventions. Therefore, future work should investigate the influence of pre-exercise dietary intake on the prolonged intermittent, high-intensity exercise performance of adolescents. This would enable quantification of whether pre-exercise nutrition can modulate exercise performance and, if so, the optimum dietary composition to achieve this. Research could then combine this knowledge with ingestion of carbohydrate-containing products during exercise to facilitate ethical and healthy nutritional guidelines for enhancing the exercise performance of adolescents. This article addresses the available evidence regarding carbohydrate supplementation and prolonged intermittent, high-intensity exercise in adolescent team games players. It discusses the potential health concerns associated with the frequent use of carbohydrate-containing products by adolescents and how this affects the research ethics of the field, and considers directions for future work.

Prevalence of hyponatremia, renal dysfunction, and other electrolyte abnormalities among runners before and after completing a marathon or half marathon

Background:

Prior reports on metabolic derangements observed in distance running frequently have small sample sizes, lack prerace laboratory measures, and report sodium as the sole measure.

Hypothesis:

Metabolic abnormalities—hyponatremia, hypokalemia, renal dysfunction, hemoconcentration—are frequent after completing a full or half marathon. Clinically significant changes occur in these laboratory values after race completion.

Study Design:

Observational, cross-sectional study.

Methods:

Consenting marathon and half marathon racers completed a survey as well as finger stick blood sampling on race day of the National Marathon to Fight Breast Cancer (Jacksonville, Florida, February 2008). Parallel blood measures were obtained before and after race completion (prerace, n = 161; postrace, n = 195).

Results:

The prevalence of prerace and postrace hyponatremia was 8 of 161 (5.0%) and 16 of 195 (8.2%), respectively. Hypokalemia was not present prerace but was present in 1 runner postrace (1 of 195). Renal dysfunction occurred prerace in 14 of 161 (8.7%) and postrace in 83 of 195 (42.6%). Among those with postrace renal dysfunction, 45.8% (38 of 83) were classified as moderate or severe. Hemoconcentration was present in 2 of 161 (1.2%) prerace and 6 of 195 (3.1%) postrace. The mean changes in laboratory values were (postrace minus prerace): sodium, 1.6 mmol/L; potassium, −0.2 mmol/L; blood urea nitrogen, 2.8 mg/dL; creatinine, 0.2 mg/dL; and hemoglobin, 0.3 g/dL for 149 pairs (except blood urea nitrogen, n = 147 pairs). Changes were significant for all comparisons (P < 0.01) except potassium (P = 0.08) and hemoglobin (P = 0.01).

Conclusions:

Metabolic abnormalities are common among endurance racers, and they may be present prerace, including hyponatremia. The clinical significance of these findings is unknown.

Clinical relevance:

It is unclear which runners are at risk for developing clinically important metabolic derangements. Participating in prolonged endurance exercise appears to be safe in the majority of racers.

Carbohydrate ingestion during team games exercise: current knowledge and areas for future investigation

There is a growing body of research on the influence of ingesting carbohydrate-electrolyte solutions immediately prior to and during prolonged intermittent, high-intensity exercise (team games exercise) designed to replicate field-based team games. This review presents the current body of knowledge in this area, and identifies avenues of further research. Almost all early work supported the ingestion of carbohydrate-electrolyte solutions during prolonged intermittent exercise, but was subject to methodological limitations. A key concern was the use of exercise protocols characterized by prolonged periods at the same exercise intensity, the lack of maximal- or high-intensity work components and long periods of seated recovery, which failed to replicate the activity pattern or physiological demand of team games exercise. The advent of protocols specifically designed to replicate the demands of field-based team games enabled a more externally valid assessment of the influence of carbohydrate ingestion during this form of exercise. Once again, the research overwhelmingly supports carbohydrate ingestion immediately prior to and during team games exercise for improving time to exhaustion during intermittent running. While the external validity of exhaustive exercise at fixed prescribed intensities as an assessment of exercise capacity during team games may appear questionable, these assessments should perhaps not be viewed as exhaustive exercise tests per se, but as indicators of the ability to maintain high-intensity exercise, which is a recognized marker of performance and fatigue during field-based team games. Possible mechanisms of exercise capacity enhancement include sparing of muscle glycogen, glycogen resynthesis during low-intensity exercise periods and attenuated effort perception during exercise. Most research fails to show improvements in sprint performance during team games exercise with carbohydrate ingestion, perhaps due to the lack of influence of carbohydrate on sprint performance when endogenous muscle glycogen concentration remains above a critical threshold of ∼200  mmol/kg dry weight. Despite the increasing number of publications in this area, few studies have attempted to drive the research base forward by investigating potential modulators of carbohydrate efficacy during team games exercise, preventing the formulation of optimal carbohydrate intake guidelines. Potential modulators may be different from those during prolonged steady-state exercise due to the constantly changing exercise intensity and frequency, duration and intensity of rest intervals, potential for team games exercise to slow the rate of gastric emptying and the restricted access to carbohydrate-electrolyte solutions during many team games. This review highlights fluid volume, carbohydrate concentration, carbohydrate composition and solution osmolality; the glycaemic index of pre-exercise meals; fluid and carbohydrate ingestion patterns; fluid temperature; carbohydrate mouthwashes; carbohydrate supplementation in different ambient temperatures; and investigation of all of these areas in different subject populations as important avenues for future research to enable a more comprehensive understanding of carbohydrate ingestion during team games exercise.

Influence of exercise on skill proficiency in soccer

The ability to maintain technical performances (i.e. skills) throughout soccer match-play is considered to be crucial in determining the outcome of competitive fixtures. Consequently, coaches dedicate a large proportion of time to practicing isolated skills, such as passing, shooting and dribbling. Unlike other elements that contribute to team-sport performances, it is unusual for coaches to use methods other than observations to assess changes resulting from technical training. Researchers have employed various tests to measure isolated soccer skills; however, reliance on outcome measures that include number of contacts (ball juggling tasks), time (dribbling tasks) and points scored (criterion-based passing and shooting tests) means that the outcomes are difficult for coaches to interpret. Skill tests that use video-analysis techniques to measure ball speed, precision and success of soccer skills offer valid and reliable alternatives. Although equivocal results are published, skill performances can be affected by assorted factors that threaten homeostasis, including match-related fatigue, dehydration and reductions in blood glucose concentrations. While acknowledging methodological constraints associated with using skill tests with limited ecological validity and cognitive demands, the effects of these homeostatic disturbances might vary according to the type of skill being performed. Shooting performances appear most susceptible to deterioration after exercise. Strategies such as aerobic training, fluid-electrolyte provision and acute carbohydrate supplementation have been found to improve proficiency in technical actions performed after soccer-specific exercise. However, mechanisms that cause deterioration in skill during soccer-specific exercise remain to be fully elucidated and strategies to optimize technical performance throughout match-play are warranted.

Ingesting a 6% carbohydrate-electrolyte solution improves endurance capacity, but not sprint performance, during intermittent, high-intensity shuttle running in adolescent team games players aged 12-14 years

The main aim of this study was to investigate the influence of consuming a 6% carbohydrate-electrolyte (CHO-E) solution on the intermittent, high-intensity endurance performance and capacity of adolescent team games players. Fifteen participants (mean age 12.7 +/- 0.8 years) performed two trials separated by 3-7 days. In each trial, they completed 60 min of exercise composed of four 15-min periods of part A of the Loughborough Intermittent Shuttle Test, followed by an intermittent run to exhaustion (part B). In a double-blind, randomised, counterbalanced fashion participants consumed either the 6% CHO-E solution or a non-carbohydrate (CHO) placebo (5 ml kg(-1) BM) during the 5 min pre-trial and after each 15-min period of part A (2 ml kg(-1) BM). Time to fatigue was increased by 24.4% during part B when CHO was ingested (5.1 +/- 1.8 vs. 4.1 +/- 1.6 min, P < 0.05), with distance covered in part B also significantly greater in the CHO trial (851 +/- 365 vs. 694 +/- 278 m, P < 0.05). No significant between-trials differences were observed for mean 15-m sprint time (P = 0.35), peak sprint time (P = 0.77), or heart rate (P = 0.08) during part A. These results demonstrate, for the first time, that ingestion of a CHO-E solution significantly improves the intermittent, high-intensity endurance running capacity of adolescent team games players during an exercise protocol designed to simulate the physiological demands of team games.

Exercise-induced homeostatic perturbations provoked by singles tennis match play with reference to development of fatigue

This review addresses metabolic, neural, mechanical and thermal alterations during tennis match play with special focus on associations with fatigue. Several studies have provided a link between fatigue and the impairment of tennis skills proficiency. A tennis player's ability to maintain skilled on-court performance and/or optimal muscle function during a demanding match can be compromised as a result of several homeostatic perturbations, for example hypoglycaemia, muscle damage and hyperthermia. Accordingly, an important physiological requirement to succeed at competitive level might be the player's ability to resist fatigue. However, research evidence on this topic is limited and it is unclear to what extent players experience fatigue during high-level tennis match play and what the physiological mechanisms are that are likely to contribute to the deterioration in performance.

The influence of carbohydrate-electrolyte ingestion on soccer skill performance

PURPOSE

To investigate the effect of ingesting a carbohydrate-electrolyte solution (CHO-E), in subjects with reduced carbohydrate stores, during an intermittent shuttle running test (LIST) on soccer passing (LSPT) and shooting (LSST) performance.

METHODS

Sixteen healthy male university soccer players ingested either a 6.4% CHO-E or placebo (PLA) solution during 90 min of the LIST (5 mL x kg(-1) BM before and 2 mL x kg(-1) BM every 15 min of exercise), in a double-blind, randomized, crossover design, with each trial separated by at least 7 d. On the evening before the main trial (17:00 h), subjects performed the glycogen-reducing cycling exercise (approximately 80 min at 70% VO2max). They were then fed a low-carbohydrate evening meal and reported to the laboratory the following morning after a 10-h fast. Blood was collected at rest and after every 30 min of exercise; skill tests were performed before and after the LIST.

RESULTS

The change in mean LSST performance from pre- to post-LIST was better in the CHO-E trial (11 +/- 45 vs -16 +/- 42%; P < 0.01) but not significantly different for the LSPT performance (-1 +/- 10% (CHO-E) vs -6 +/- 13% (PLA), P = 0.13). Sprint performance during the LIST was quicker in the CHO-E trial (2.50 +/- 0.13 vs 2.53 +/- 0.13 s, P < 0.01). Plasma glucose was higher in the CHO-E trial after 90 min of exercise (5.2 +/- 0.3 vs 3.9 +/- 0.4 mM, P < 0.01).

CONCLUSIONS

Ingestion of a carbohydrate-electrolyte solution during exercise enabled subjects with compromised glycogen stores to better maintain skill and sprint performance than when ingesting fluid alone.

Fluid and fuel intake during exercise

The amounts of water, carbohydrate and salt that athletes are advised to ingest during exercise are based upon their effectiveness in attenuating both fatigue as well as illness due to hyperthermia, dehydration or hyperhydration. When possible, fluid should be ingested at rates that most closely match sweating rate. When that is not possible or practical or sufficiently ergogenic, some athletes might tolerate body water losses amounting to 2% of body weight without significant risk to physical well-being or performance when the environment is cold (e.g. 5-10 degrees C) or temperate (e.g. 21-22 degrees C). However, when exercising in a hot environment ( > 30 degrees C), dehydration by 2% of body weight impairs absolute power production and predisposes individuals to heat injury. Fluid should not be ingested at rates in excess of sweating rate and thus body water and weight should not increase during exercise. Fatigue can be reduced by adding carbohydrate to the fluids consumed so that 30-60 g of rapidly absorbed carbohydrate are ingested throughout each hour of an athletic event. Furthermore, sodium should be included in fluids consumed during exercise lasting longer than 2 h or by individuals during any event that stimulates heavy sodium loss (more than 3-4 g of sodium). Athletes do not benefit by ingesting glycerol, amino acids or alleged precursors of neurotransmitter. Ingestion of other substances during exercise, with the possible exception of caffeine, is discouraged. Athletes will benefit the most by tailoring their individual needs for water, carbohydrate and salt to the specific challenges of their sport, especially considering the environment's impact on sweating and heat stress.

Nutrition on match day

What players should eat on match day is a frequently asked question in sports nutrition. The recommendation from the available evidence is that players should eat a high-carbohydrate meal about 3 h before the match. This may be breakfast when the matches are played around midday, lunch for late afternoon matches, and an early dinner when matches are played late in the evening. The combination of a high-carbohydrate pre-match meal and a sports drink, ingested during the match, results in a greater exercise capacity than a high-carbohydrate meal alone. There is evidence to suggest that there are benefits to a pre-match meal that is composed of low-glycaemic index (GI) carbohydrate foods rather than high-GI foods. A low-GI pre-match meal results in feelings of satiety for longer and produces a more stable blood glucose concentration than after a high-GI meal. There are also some reports of improved endurance capacity after low-GI carbohydrate pre-exercise meals. The physical demands of soccer training and match-play draw heavily on players' carbohydrate stores and so the benefits of good nutritional practices for performance and health should be an essential part of the education of players, coaches, and in particular the parents of young players.

Dietary supplements and sports performance: minerals

Minerals are essential for a wide variety of metabolic and physiologic processes in the human body. Some of the physiologic roles of minerals important to athletes are their involvement in: muscle contraction, normal hearth rhythm, nerve impulse conduction, oxygen transport, oxidative phosphorylation, enzyme activation, immune functions, antioxidant activity, bone health, and acid-base balance of the blood. The two major classes of minerals are the macrominerals and the trace elements. The scope of this article will focus on the ergogenic theory and the efficacy of such mineral supplementation.

Effects of Acute Chromium Supplementation on Postprandial Metabolism in Healthy Young Men

BACKGROUND

Chromium (Cr) potentiates the action of insulin in the cell and improves glucose tolerance after long-term supplementation.

OBJECTIVE

We hypothesized that Cr may also have acute effects and might be beneficial in lowering the glycemic index of a meal.

METHODS

We studied the effects of short-term Cr supplementation using a randomized crossover design. Thirteen apparently healthy, non-smoking young men of normal body mass index performed three trials each separated by one week. Test meals, providing 75 g of available carbohydrates, consisted of white bread with added Cr (400 or 800 microg as Cr picolinate) or placebo.

RESULTS

After addition of 400 and 800 microg Cr incremental area under the curve (AUC) for capillary glucose was 23% (p = 0.053) and 20% (p = 0.054), respectively, lower than after the white bread meal. These differences reached significance if the subjects were divided into responders (n = 10) and non-responders (n = 3). For the responders AUC after 400 and 800 microg Cr was reduced by 36% and 30%, respectively (Placebo 175 +/- 22, Cr400 111 +/- 14 (p < 0.01), Cr800 122 +/- 15 mmol. min/L (p < 0.01)). Glycemia was unchanged after addition of Cr in the non-responders. Responders and non-responders differed significantly in their nutrient intake and eating pattern, and total serum iron concentration tended to be lower in the responder group (p = 0.07).

CONCLUSIONS

Acute chromium supplementation showed an effect on postprandial glucose metabolism in most but not all subjects. The response to Cr may be influenced by dietary patterns.

Effects of a Commercial Herbal-Based Formula on Exercise Performance in Cyclists

INTRODUCTION/PURPOSE

We examined the effects of a commercially marketed herbal-based formula purported to increase endurance on oxygen consumption (VO2) in 17 competitive category III/IV amateur cyclists [mean (SEM) age: 31.1 (1.8) yr; height: 178.5 (1.8) cm; weight: 77.1 (1.6) kg].

METHODS

Each cyclist participated in two (pre/post) cycling tests progressing 25 W.4 min(-1) starting at 100 W administered in a randomized, placebo-controlled, double-blind fashion. The second trial was performed 14 d after the ingestion of a manufacturer recommended loading phase (4 d x 6 caps.d(-1)) and a maintenance phase (11 d x 3 caps.d(-1)). Three treatment capsules contained 1000 mg of Cordyceps sinensis (CS-4) and 300 mg Rhodiola rosea root extract as the primary ingredients; 800 mg of other ingredients included calcium pyruvate, sodium phosphate, potassium phosphate, ribose, and adenosine and 200 mcg of chromium.

RESULTS

Using a 2 x 2 ANOVA, we observed no significant treatment effect for any between or within group variables including peak VO2 [treatment 4.14 (0.2) L.min(-1); placebo 4.10 (0.2) L.min(-1)], time to exhaustion [treatment 38.47 (1.7) min; placebo 36.95 (1.8) min], peak power output (PO) [treatment 300.00 (12.1) W; placebo 290.63 (12.9) W], or peak heart rate. We also observed no differences for any subpeak exercise variable including the PO eliciting 2 mmol.L(-1) blood lactate (BLa) [treatment 201.00 (18.1) W; placebo 167.50 (19.2) W] and 4 mmol.L(-1) BLa [treatment 235.88 (15.8) W; placebo 244.78 (14.9) W], ventilatory threshold, respiratory compensation point, or Vo2 L.min(-1) gross efficiency at each stage.

CONCLUSION

A 2-wk ingestion schema of a commercial herbal-based formula is insufficient to elicit positive changes in cycling performance.

The potential value and toxicity of chromium picolinate as a nutritional supplement, weight loss agent and muscle development agent

The element chromium apparently has a role in maintaining proper carbohydrate and lipid metabolism in mammals. As this role probably involves potentiation of insulin signalling, chromium dietary supplementation has been postulated to potentially have effects on body composition, including reducing fat mass and increasing lean body mass. Because the supplement is absorbed better than dietary chromium, most studies have focused on the use of chromium picolinate [Cr(pic)(3)]. Cr(pic)(3) has been amazingly popular with the general public, especially with athletes who may have exercise-induced increased urinary chromium loss; however, its effectiveness in manifesting body composition changes has been an area of intense debate in the last decade. Additionally, claims have appeared that the supplement might give rise to deleterious effects. However, over a decade of human studies with Cr(pic)(3) indicate that the supplement has not demonstrated effects on the body composition of healthy individuals, even when taken in combination with an exercise training programme. Recent cell culture and in vivo rat studies have indicated that Cr(pic)(3) probably generates oxidative damage of DNA and lipids and is mutagenic, although the significance of these results on humans taking the supplement for prolonged periods of time is unknown and should be a focus for future investigations. Given that in vitro studies suggest that other forms of chromium used as nutritional supplements, such as chromium chloride, are unlikely to be susceptible to generating this type of oxidative damage, the use of these compounds, rather than Cr(pic)(3), would appear warranted. Potential neurological effects (both beneficial and deleterious) from Cr(pic)(3) supplementation require further study.

Chromium picolinate for reducing body weight: meta-analysis of randomized trials

The aim of this meta-analysis was to assess the evidence of chromium picolinate for reducing body weight. Literature searches were conducted on Medline, Embase, The Cochrane Library, Amed and Ciscom. Nine experts and four manufacturers of commercial preparations containing chromium picolinate were asked to contribute published and unpublished studies. There were no restrictions regarding the language of publication. The screening of studies, selection, data extraction, validation and the assessment of methodological quality were performed independently by two reviewers. To be included, studies were required to state that they were randomized, double-blind and placebo-controlled, and report on body weight. Ten trials met all inclusion criteria and provided data, which were suitable for statistical pooling. For body weight a significant differential effect was found in favour of chromium picolinate (weighted mean difference: -1.1 kg; 95% confidence interval (CI): -1.8 to -0.4 kg, n=489). Sensitivity analysis suggests that this effect is largely dependent on the results of a single trial (weighted mean difference: -0.9 kg; 95% CI: -2.0 to 0.2 kg, n=335). Three of the reviewed trials reported on adverse events, indicating their absence in the treatment groups. In conclusion, our meta-analysis suggests a relatively small effect of chromium picolinate compared with placebo for reducing body weight. The clinical relevance of the effect is debatable and the lack of robustness means that the result has to be interpreted with caution.

Magnesium, zinc, and chromium nutrition and athletic performance

Magnesium, zinc and chromium are mineral elements required in modest amounts for health and optimal performance. Accumulating evidence supports the hypothesis that magnesium and zinc play significant roles in promoting strength and cardiorespiratory function in healthy persons and athletes. Differences in study designs, however, limit conclusions about recommendations for intakes of magnesium and zinc needed for optimal performance and function. The role of chromium in supporting performance is not well established. There is a compelling need to confirm and extend findings of beneficial effects of magnesium and zinc function and performance of humans. Suggestions for an experimental model and specific topics for research to advance knowledge of mineral nutrition to promote attainment of genetic potential for optimal performance are provided.