SPORTSCIENCE

sportsci.org

Perspectives: Nutrition

FLUID AND CARBOHYDRATE INTAKE DURING TEAM GAMES: Research and Recommendations

Louise M Burke PhD

Department of Sports Nutrition, Australian Institute of Sport, Belconnen 2616, Australia. Email: lburke=AT=ausport.gov.au

Sportscience 3(1), sportsci.org/jour/9901/lmb.html, 1999 (1733 words)

Reviewed by Mark Hargreaves PhD, School of Health Sciences, Deakin University, Burwood 3125, Australia

Performance in team sports is determined by a complex mixture of physical fitness and mental skills. Players may have to run quickly to the ball or scene of play, perform maneuvers involving strength, and execute skills involving cognitive function and fine motor control. Nutritional strategies could impact these physical and mental components of performance.

Exercise-science and sports-nutrition organizations have produced position stands or recommendations about the intake of fluid and carbohydrate during exercise. Typically these guidelines target the requirements of sports involving prolonged continuous exercise, such as running or cycling, and are based on research of such exercise. How well the guidelines meet the needs of team-sport athletes is not clear, because the fluid and carbohydrate needs of team players differ from those of endurance athletes in several ways. Table 1 identifies some of the unique characteristics of team sports with regard to fluid balance.

I recently co-authored a review of the published data on sweat loss, fluid intake, and fluid balance during team games (Burke and Hawley, 1997). We were surprised by the scarcity of data from actual competitions, and by the failure of these data to cover the range of environmental conditions and levels of play that are of interest. Our impression is that fluid intake generally falls behind sweat loss during team games, and that moderate to severe dehydration can occur. We also noted that data on the use of carbohydrate-containing drinks to promote fuel replacement during matches are not available. Fuel requirements vary between team sports: tournament play in particular must pose the greatest challenge to the fuel status of players, especially when the match schedule does not allow enough time for restoration of muscle glycogen between games.

Why is there so little performance-based research on nutrition in team sports? The main reason is probably that performance is difficult to measure in team sports. In most other sports, the athlete competes as an individual and achieves a certain time, distance or weight. Although there are problems of design and analysis in research on these sports (Hopkins et al., 1999), finding a test that simulates a competitive event is relatively straight forward. Team sports, on the other hand, involve competition between opponents; each game therefore develops in a relatively unique fashion, and performance depends on the relative ability of the opponent. Researchers have used three approaches to try to overcome this problem: they assay performance in isolated tests, in simulated matches, or in real matches.

In the first approach, the researchers use performance tests that mimic physical demands or skills involved in a game, for example repeated high-intensity running with brief recovery time, or a task involving reaction time or decision-making. The researchers should use well-trained team athletes as subjects and administer the intervention and placebo treatments in a double-blind fashion. If the test involves a novel task, especially an isolated task of skill or fine motor control, the subjects should have familiarization trials to reduce learning effects. A reliable test will increase the precision of the estimate of change in performance, as will the use of a cross-over design. The major limitation of such studies is in the validity of the performance measure: how well do changes in an isolated physical or cognitive task translate into on-field performance? Although characteristics such as concentration, reaction time, or the ability to recover between repeated sprints may be important features in a game, it is difficult to extrapolate from an isolated feature to the game. For example, a cognitive skill may deteriorate with dehydration in a laboratory setting, but psychological arousal in a competition may compensate for the deficit. Alternatively, the overlay of a number of performance demands, such as controlling a ball or withstanding tackles, may add to deterioration in the primary task.

The second approach involves simulating a game, either in the field or on ergometers or custom-built equipment in the lab. Different types of performance measurement may be taken before, during, and after the game. Again, the characteristics of well-controlled studies should be applied. The simulation should also be as close to real play as possible, and involve reliable performance tasks. The diet and training status of subjects before and during the study should be standardized between trials and should represent real-life conditions of competitive play. For example, subjects should be fed a standard pre-match meal and undertake supervised work-outs on the days prior to the game. This type of design allows a similar game to be played for the different treatments, but the major limitation is the validity of the performance tasks: these tasks are not integrated into game play, so they may not reflect on-field competitive performance.

The third approach involves real matches, staged for the study. Time-and-motion analyses or scores of errors and successful plays in the games provide measures of performance. These measures have better validity than measures in the other types of study, but their reliability may be low, owing to variability between matches. To reduce this variability, researchers have arranged for two teams to play each other on a number of occasions, and they have assigned half of each team to the treatment and placebo. In other studies researchers have assigned athletes in similar playing positions within the same team to the treatment and placebo.

A small number of studies have used these different designs to measure the effects of hydration status and carbohydrate feeding during a match. Not surprisingly, some studies provide evidence that carbohydrate and fluid intake enhances performance, whereas others claim no effect. These differences in outcome may reflect nothing more than lack of precision in the estimates of change in performance, but it is also possible that these strategies really do have different effects in different situations. For example, hydration and refueling may be of more benefit in matches that involve a longer duration of play, or for players who are involved in most of the game activity. Similarly, the effects of dehydration and carbohydrate depletion are likely to be more pronounced when athletes play matches in hot conditions.

The challenge for sports scientists is to develop better research tools to monitor the success of nutritional strategies. Meanwhile, those of us who work in team sports must continue to guide our athletes with common-sense recommendations. Here is a summary of the recommendations in our review, based on intuition and personal experience rather than objective evidence of performance benefits.

• In hot environments, be aware of factors that can affect heat accumulation during training or competition: time of day, length of play, conditions in indoor venues, and suitability of uniforms or protective gear.
• Players should track sweat losses in different environments by weighing themselves regularly before and after training sessions. Use the data to identify individuals at risk of dehydration and to implement a team fluid-intake plan.
• Players must begin each match properly hydrated. Fluid losses from previous matches or training need to be restored. It is also useful to drink immediately before a game. Players can learn to tolerate up to 5 ml per kg during the warm-up.
• Opportunities to consume fluid during the game should be optimized. Ideally, players should consume fluid every 10-15 minutes. If rules of the game prevent this practice, players may be able to find ways that work within the regulations.
• Players drink more pleasant-tasting sports drinks than plain water. Sports drinks have the extra advantage of providing energy in situations where liver and muscle glycogen stores are likely to be depleted.
• Post-match rehydration is an important part of recovery. Use drinks containing substantial amounts of carbohydrate and salts. Avoid excessive intake of alcohol.
• Players should practice the strategies in training so they can implement them successfully in competition.

Burke LM, Hawley JA (1997). Fluid balance in team sports: guidelines for optimal practices. Sports Medicine 24, 38-54

Hopkins WG, Hawley JA, Burke LM (1999). Design and analysis of research on sport performance enhancement. Medicine and Science in Sports and Exercise 31, 472-485.