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: email@example.com
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 ofphysical fitness and mental skills. Players may have to run quicklyto the ball or scene of play, perform maneuvers involving strength,and execute skills involving cognitive function and fine motorcontrol. Nutritional strategies could impact these physical andmental components of performance.
Exercise-science and sports-nutrition organizations have producedposition stands or recommendations about the intake of fluid andcarbohydrate during exercise. Typically these guidelines target therequirements of sports involving prolonged continuous exercise, suchas running or cycling, and are based on research of such exercise.How well the guidelines meet the needs of team-sport athletes is notclear, because the fluid and carbohydrate needs of team playersdiffer from those of endurance athletes in several ways. Table 1identifies some of the unique characteristics of team sports withregard to fluid balance.
I recently co-authored a review of the published data on sweatloss, fluid intake, and fluid balance during team games (Burkeand Hawley, 1997). We were surprised by the scarcity of data fromactual competitions, and by the failure of these data to cover therange of environmental conditions and levels of play that are ofinterest. Our impression is that fluid intake generally falls behindsweat loss during team games, and that moderate to severe dehydrationcan occur. We also noted that data on the use ofcarbohydrate-containing drinks to promote fuel replacement duringmatches are not available. Fuel requirements vary between teamsports: tournament play in particular must pose the greatestchallenge to the fuel status of players, especially when the matchschedule does not allow enough time for restoration of muscleglycogen between games.
Why is there so little performance-based research on nutrition inteam sports? The main reason is probably that performance isdifficult to measure in team sports. In most other sports, theathlete competes as an individual and achieves a certain time,distance or weight. Although there are problems of design andanalysis in research on these sports (Hopkins et al.,1999), finding a test that simulates a competitive event isrelatively straight forward. Team sports, on the other hand, involvecompetition between opponents; each game therefore develops in arelatively unique fashion, and performance depends on the relativeability of the opponent. Researchers have used three approaches totry to overcome this problem: they assay performance in isolatedtests, in simulated matches, or in real matches.
In the first approach, the researchers use performance tests thatmimic physical demands or skills involved in a game, for examplerepeated high-intensity running with brief recovery time, or a taskinvolving reaction time or decision-making. The researchers shoulduse well-trained team athletes as subjects and administer theintervention and placebo treatments in a double-blind fashion. If thetest involves a novel task, especially an isolated task of skill orfine motor control, the subjects should have familiarization trialsto reduce learning effects. A reliable test will increase theprecision of the estimate of change in performance, as will the useof a cross-over design. The major limitation of such studies is inthe validity of the performance measure: how well do changes in anisolated physical or cognitive task translate into on-fieldperformance? Although characteristics such as concentration, reactiontime, or the ability to recover between repeated sprints may beimportant features in a game, it is difficult to extrapolate from anisolated feature to the game. For example, a cognitive skill maydeteriorate with dehydration in a laboratory setting, butpsychological arousal in a competition may compensate for thedeficit. Alternatively, the overlay of a number of performancedemands, such as controlling a ball or withstanding tackles, may addto deterioration in the primary task.
The second approach involves simulating a game, either in thefield 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 ofwell-controlled studies should be applied. The simulation should alsobe as close to real play as possible, and involve reliableperformance tasks. The diet and training status of subjects beforeand during the study should be standardized between trials and shouldrepresent real-life conditions of competitive play. For example,subjects should be fed a standard pre-match meal and undertakesupervised work-outs on the days prior to the game. This type ofdesign allows a similar game to be played for the differenttreatments, but the major limitation is the validity of theperformance tasks: these tasks are not integrated into game play, sothey 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 inthe games provide measures of performance. These measures have bettervalidity than measures in the other types of study, but theirreliability may be low, owing to variability between matches. Toreduce this variability, researchers have arranged for two teams toplay each other on a number of occasions, and they have assigned halfof each team to the treatment and placebo. In other studiesresearchers have assigned athletes in similar playing positionswithin the same team to the treatment and placebo.
A small number of studies have used these different designs tomeasure the effects of hydration status and carbohydrate feedingduring a match. Not surprisingly, some studies provide evidence thatcarbohydrate and fluid intake enhances performance, whereas othersclaim no effect. These differences in outcome may reflect nothingmore than lack of precision in the estimates of change inperformance, but it is also possible that these strategies really dohave different effects in different situations. For example,hydration and refueling may be of more benefit in matches thatinvolve a longer duration of play, or for players who are involved inmost of the game activity. Similarly, the effects of dehydration andcarbohydrate depletion are likely to be more pronounced when athletesplay matches in hot conditions.
The challenge for sports scientists is to develop better researchtools to monitor the success of nutritional strategies. Meanwhile,those of us who work in team sports must continue to guide ourathletes with common-sense recommendations. Here is a summary of therecommendations in our review, based on intuition and personalexperience rather than objective evidence of performancebenefits.
Hopkins WG, Hawley JA, Burke LM (1999). Design and analysis ofresearch on sport performance enhancement. Medicine and Science inSports and Exercise 31, 472-485.