Half-time nutrition – what’s best for maximising fulltime performance?

Half-Time Training for Team Sports

Half-time nutrition – what’s best for maximising fulltime performance?

The days of sliced oranges and a cup tea at half-time are long gone. As Tim Lawson explains, optimum half-time nutrition is a complex science in which a number of factors need to be considered

The half-time nutritional strategies employed by many sports teams often rely as much on tradition, fashion and even sponsorship deals as they do on sound science. But with sports like football becoming so high profile, nutritional strategies are becoming increasingly sophisticated, with many teams employing full-time nutritionists and sport scientists. Increasingly, top teams are using specialist sports drinks and other products with an emphasis on different priorities for different positions and individuals.

The traditional approach to half-time nutrition usually involves a cup of tea and a slice of orange, and like many nutritional practices that have stood the test of time, this almost certainly has some merit. Similarly, other foods such as high-carbohydrate cakes, confectionery and even jelly babies have been advocated because they contain useful energy. Some scientific papers have even recommended snacks like pretzels because they contain high levels of sodium(1).

However, these kinds of products may also contain other ingredients that are not entirely beneficial for sports performance. For instance, it may not be possible to measure the performance detriments of hydrogenated vegetable oils or trans-fats in a single game but their negative effects on health are well documented, which is why they’re banned in several countries. Similarly, colourings and other additives are often contained in these kinds of products, which have at least been associated with disruptive behaviour and poor concentration in school children, if not some of the crazy on- and off-ball fouls often seen on TV(2)!

So what are the main factors to consider when planning nutrition in the half-time interval? Since the first World Congress on the Science of Football was held at Liverpool in 1987, there has been much published research on the physical demands of football and other team sports, and the nutritional status of participants. Fluid, electrolyte and carbohydrate needs have been studied during training and in match simulations, as well as the effects of dietary manipulations on sport-specific skills. Fatigue has been observed as a transient phenomenon during matches and general performance declines towards the end of matches. However, the underlying factors responsible for fatigue during football are still not fully understood(3,4).

There have been very few studies that have looked specifically at a nutritional intervention at half-time and its effect on performance in the second half. An as yet unpublished study, presented at the 2006 American College of Sports Medicine annual meeting, showed that players who had been fed a mixture of protein and carbohydrates at half-time performed worse in the second half than those given a carbohydrate drink. However, the principles for effective nutritional strategies need to be deduced from the research based on the demands of the game and the factors known to limit physical performance. Case studies are therefore important.

Physical demands of team sports

There are significant differences in the physical demands of team sports like soccer, American football and rugby, with soccer being more physically demanding in terms of distance covered per minute than rugby, for instance(5). However, most team sports show activity patterns that would be expected to have a considerable energy cost, with typical values for distance covered per match at around 8-11km.

The energy cost of competing in a match is much higher than an even-paced run of the same distance, as there are numerous changes of pace with many periods of intense activity, which is typically associated with heavy demands on carbohydrate energy supply(4). Within the same sport, different league standards are often associated with different activity levels, with top-class sport clearly differentiated from lower levels by the increased volume of high-intensity play(3).

Outcomes in team sports are highly influenced by skill, so it is also important to consider factors that may influence skill and concentration when considering strategies to optimise performance. Often these factors go hand in hand with carbohydrate depletion, associated with reduced exercise capacity and poor concentration – effects that may be compounded by dehydration. Both dehydration and muscle glycogen depletion have been associated with injury and accidents, so efforts to prevent these affecting performances could have repercussions well beyond the immediate match.

One of the main difficulties in discussing nutritional strategies for the half-time interval in order to optimise performance in the second half is that the factors may vary according to the state that players are in prior to the match. In the early 1990s, scientific publications commenting on nutrition for football tended to suggest that even when players were consuming sufficient calories to meet their energy needs, they should consume more carbohydrate in order to recover between training sessions and to maximise muscle glycogen stores prior to a match(6,7).

More recent publications, whilst stressing the importance of replenishing muscle glycogen stores between training sessions and the potential benefits of carbohydrate loading for matches, have also warned about the over-consumption of carbohydrate if optimal body composition is to be achieved(8).

However, studies using dietary analysis continue to suggest that many soccer players are failing to consume sufficient carbohydrate to optimise carbohydrate stores(9) and two Spanish studies published in 2005 suggested that the eating habits of young players were so poor that nutritional intervention and education was necessary in order to improve general healthy dietary practices(6,7).

The impact of carbohydrate supplementation during the half-time interval could well depend upon the prior eating habits of the player. Similarly, the rehydration needs, and therefore the efficacy of half-time rehydration strategies, will depend on the pre-game hydration status as much as the playing conditions and player work rates. Researchers from Pennsylvania State University recently investigated the effect of dehydration and rehydration on basketball skill. Urine tests showed that some subjects taking part in the experiment were already dehydrated when they arrived at the experiment venue, even though they had been encouraged to stay well hydrated the day before each trial(10).

This situation is probably reflected in real game situations, especially where squads are not monitored closely in their build-up to games. Sport nutritionists working with Premier League football clubs have noted that players often turn up to training less optimally hydrated during cold weather than in the hotter months. This may be because players give hydration less priority when the sun is not shining and are unaware of the increased water vapour losses in cold conditions.

The growing use of under-pitch heating also means that more games can be played in very cold air temperatures, where water vapour losses are significant. If well-monitored players at high levels of sport are often sub-optimally hydrated, there’s a good chance that players in other leagues are starting matches in a sub-optimal state and will therefore be in a worse state at half-time than necessary.

Just enough and no more

Scientific studies of sub-elite sportsmen and women show there is much to be gained by replacing fatty, energy-dense foods with more carbohydrate(11,12). However, at the very elite end of sport, nutritionists are fine-tuning energy and hydration provision to provide just enough.

This is to maximise power-to-weight ratio; each gram of carbohydrate stored as muscle glycogen is bound to 3g of water, so if a player starts with 500g of muscle glycogen and this is used during the game it will release 1.5kg of water. This released water is important when considering the fluid and energy requirements at half-time.

While dehydration resulting in a loss of body mass of 2% or greater can result in reduced endurance exercise capacity, and sprinting and sport-specific skills can be adversely affected by losses of 3% or more(3,10), players are able to tolerate a level of dehydration. There’s no merit in encouraging players to consume more fluid than required to maintain performance, because this would be the equivalent of sending players out with a weight vest! However, any change in body mass should not be calculated by the difference between that immediately prior to the match and half-time, but instead baseline body mass should be established by early morning measurements taken before any carbohydrate loading has taken place(13).

Although there are some reports of soccer players losing up to four or five litres per hour of sweat in very hot and humid environments and up to three litres in temperate climates, sweat losses closer to two litres per hour are probably more typical(1, 3,13). In such cases, a half-time fluid consumption of between 500 and 800mls should be sufficient to prevent a decrease in body mass greater than 1% during the second half.

Individual differences

Recent publications studying the sweat response and water and electrolyte needs of footballers have noted that there are wide individual differences amongst the same teams that were not position dependant(1,13). In an ideal world each individual would have a specific fine-tuned nutritional strategy, but this can be almost impossible in the squad culture that tends to exist in everyday training situations.

Nutrients, especially electrolytes, may prevent fatigue and reduce muscle cramps in the second half. The most important electrolyte lost in sweat is sodium and research has shown a wide individual variation in sodium losses – as low as the equivalent of 1g of salt to over 6g in 90 minutes. Assuming that players start a match with reasonable sodium stores, most players are unlikely to become performance limited due to sodium depletion during one match; the main role of sodium in a half-time situation is to encourage fluid uptake in situations where large fluid volumes need to be consumed at half-time (because sodium stimulates thirst).

However, 6g is the suggested total maximum daily salt allowance recommended by the UK Food Standards Agency and there has been considerable pressure from the government for food producers to reduce the amount of sodium in food(14). It is not clear if ‘high sodium sweaters’ are so because they consume a high-sodium diet or for other reasons. It is clear, however, that sweat losses of 6g in 90 minutes cannot be sustained unless consumption is increased beyond the current recommended daily maximum. Unseasonably hot weather and reduced sodium foods may combine to leave players potentially short of this important electrolyte.

Research on many games players suggests that the status of other nutrients is often poor(9,12,15), and minerals such as zinc, magnesium and calcium (found as electrolytes in sweat) and other minerals such as iron(16) may be sub-optimal prior to matches. Whilst a player suffering from fatigue or cramps due to poor nutrition prior to the match may benefit from carbohydrate/electrolyte supplementation at half-time, it’s probably better to improve diet between matches rather than try to patch up poor general nutrition with a half-time fix.

Half-time carbohydrate

In players starting with an adequate nutritional status, fluid or electrolyte losses are not usually a limiting factor in performance towards the end of games. However, carbohydrate shortfalls are almost certainly responsible for fatigue in games, irrespective of player position or standard. Low carbohydrate levels can compromise mental skills as well as physical performance, and there is consensus that carbohydrate supplementation can improve performance. Muscle glycogen stores are generally quite low at the end of games, and even when overall stores are not depleted, carbohydrate may be depleted in specific limiting muscle fibres(3).

Carbohydrate supplementation to replace lost muscle glycogen makes sense and has been shown to help prevent deterioration in the performance of soccer players in simulated matches(15) and to improve performance in soccer- and basketball-specific tests(10,17). However, gastric-emptying studies have shown that the activity levels in competitive games are such that they are likely to delay gastric emptying and possibly reduce the effectiveness of carbohydrate drinks given immediately prior to or during matches(18).

To counteract slow gastric emptying, glucose polymers (maltodextrins) have been recommended for many years; they have a lower osmolality than simple sugars, can improve gastric emptying and are relatively light on the stomach(19). Recent research from Birmingham University suggests that energy drinks using multiple energy substrates may result in improved energy delivery to the muscles(20). Combinations of maltodextrin and fructose would therefore seem to be a sensible combination to form the basis of a half-time nutritional strategy, combining good gastric emptying with the benefits of multiple energy substrate transport across the small intestine.

Half-time is, however, relatively short and care should be taken to maximise the opportunity to refuel when gastric emptying is not limited by intense match activity. Isotonic energy gels can be a practical solution, providing players with a bolus dose of carbohydrate as they leave the field, gaining valuable recovery time over a team waiting until they reach the changing rooms to get drinks. Although this article is about half-time nutritional strategies, it also makes sense to use any natural breaks in the game to take on carbohydrate, and fluid/electrolytes in hot conditions.

It’s worth cautioning against a ‘one size fits all’ policy with regard to player nutrition. A strategy of ensuring that each player consumes at least 400-500mls of 10-12% glucose polymer/fructose solution is a good baseline for half-time refuelling. In hot conditions, and for players with very high sweat rates, more fluid may be needed to prevent dehydration reaching detrimental levels. Fluid requirements can be checked by comparing half-time weights to baseline measures in training matches, and players should be encouraged to fine-tune their thirst perception using this feedback. When 800mls or more of fluid needs to be drunk at half-time, it is possibly useful to consume solutions containing at least some electrolyte, especially sodium.

References
1. Int J Sports Med 2005 Mar; 26(2):90-95
2. Arch Dis Child 2004; 89:506-511
3. J Sports Sci 2006 Jul; 24(7):665-74
4. Sports Med 2005; 35(6):501-36
5. Science and Football: Proceedings of the Second World Congress of Science and Football, 1991, Spon Press (Oct 1992)
6. Med Sci Sports Exerc 1993 Dec; 25(12):1370-4
7. J Sports Sci 1994 Summer; 12 Spec No:S43-50
8. J Sports Sci 2006 Jul; 24(7):675-85
9. Int J Sport Nutr Exerc Metab 2003 Sep; 13(3): 303-19
10. Med Sci Sports Exerc 2006; 38(9):1650-1658
11. Can J Appl Physiol 2005 Feb; 30(1):18-32
12. J Sports Sci 2005 Mar; 23(3):235-42
13. J Sports Sci 2006 Jul; 24(7):699-707
14. UK FSA (www.salt.gov.uk)
15. J Sports Sci Med 2004; 3, 198-202
16. J Sports Sci Med 2006; 5, 130-137
17. J Sports Sci Med 2002; 1, 47-53
18. Med Sci Sports Exerc 2001; 33(11): 1932-1938
19. Sports Med 1987 May-Jun; 4 (3):164-76
20. Med Sci Sports Exerc 2004; 36(9):1551-1558

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