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The science of football: Refuelling during exercise

Let me set the scene. We’re 60 minutes into a football match, a player goes down injured, the referee halts the game and medical staff dash onto the pitch to treat the injured player.

As a result, the players on the pitch typically display one of two behaviours; 1. Surround the injured player or 2. Run to the sideline where the coach provides some form of nutritional intervention i.e. the provision of fluid or a gel bar.

But why is this the first port of call by players during a break in play and specifically, what is the science behind this type of behaviour?

Athletes and coaches alike are well aware that performance improvements can result from the ingestion of carbohydrate sources during the latter phases of soccer competition which is a crucial period of match play when most goals are scored (Jinshen, Xioke, Yamonakak, & Matsumo, 1991).

The food and fluid consumed during this time forms a specific, short-term strategy aimed at maximising performance at that particular time.

There have been several mechanisms postulated in the scientific literature which pronounce how carbohydrate intake during exercise may delay fatigue, these include:
• Maintain blood glucose
• Glycogen sparing
• Promote glycogen synthesis
• Enhancement of motor skills
• Central nervous system effects

Research finding ‘23% of goals scored in 2010-2011 Premier League season were scored between 76 and 90 minutes.’

Practical strategies

Amount of carbohydrate needed - Ideally players want the amount that gives the maximum carbohydrate oxidation rate and least amount of GI* discomfort. Whilst a topic of debate within the scientific literature, current guidelines promote the ingestion of 70g/hour (1.2g/min) – any higher may cause GI distress i.e. gas, bloating, nausea or stomach upset (Jeukendrup, 2010).

*GI (Glycemic Index) - a method of ranking carbohydrates based on their blood glucose and insulin responses.

Form of carbohydrate (solid or liquid) - In a classic study by Mason et al (1993) it was found when comparing solid vs liquid, that both forms of carbohydrate intake increased glucose and insulin to similar levels and there was no difference in respiratory exchange ratio, heart rate, or oxygen uptake.

In terms of practicality I would therefore suggest football players consume liquid as oppose to solid forms of carbohydrate as this will help avoid stomach upset and promote hydration. Should a player complain of hunger, a gel bar may be an adequate source.

Timing - If possible, feed every 10-20 minutes during competition. This allows for a steady flow of carbs from the gut to the bloodstream. Avoid a large bolus dose (30-60g) at the beginning and then stop as this may incur a hypoglycaemic rebound*.

*Hypoglycaemic rebound – a sudden rise in insulin levels found to reduce lipolysis and fat oxidation. As a result carbohydrate utilisation increases and time to fatigue is markedly reduced due to a paucity of readily available energy.

A supporting football-specific research study - Currell et al. (2009) evaluated the effect of carbohydrate intake on football performance. Eleven University footballers were recruited and asked to perform three football-specific trials in a randomised order.

A carbohydrate beverage (a 7.5% maltodextrin solution) or placebo was ingested throughout exercise. Results revealed a significant improvement in various performance parameters (dribbling, agility, and shooting) when a carbohydrate beverage was consumed during exercise performance compared with placebo.

Caffeine intake: A contemporary approach – Foskett et al. (2009) examined the influence of caffeine on performance during simulated football activity.

Twelve male footballers were recruited and asked to consume 6mg of caffeine per kg of body mass or placebo 60 minutes prior to exercise on two separate occasions.

Each trial comprised of a 90 minute football-specific intermittent running protocol interspersed with tests of football skill. It was reported that caffeine ingestion prior to exercise improved passing accuracy and jump performance without any detrimental effects on other performance parameters.

Summary – The intake of fluid and carbohydrate during exercise is well documented to improve football performance, particularly in the latter phases of competition when most goals are scored.

Evidence on the beneficial effects of carbohydrate intake during exercise performance has existed for several decades, yet sports scientists are still to unearth the optimal dose, form and combinations (i.e. carbohydrate + caffeine) of intake and explain the mechanisms involved.

By Scott Robinson - scottr38@hotmail.co.uk

Scott Robinson is a First Class Honours Sport Science graduate from the only five star rated Sports Science Research Institute in the UK; Liverpool John Moores University. He has acquired a wide range of experience in both playing and coaching sport with a career high of representing Stoke City at youth level and coaching football at the International Youth Games.
Scott has previously been responsible for leading five sports scientists on placement with Blackburn Rovers' nutrition department. He has completed sports science work for FIFA, where he travelled across Europe performing a multitude of sports science tests, and has also worked as a physical education teaching assistant at a high school in Cheshire.
Scott is currently undertaking a Masters of Science in Sports Physiology, also at LJMU, specialising in sports nutrition where his research focuses on assessing and enhancing the nutritional knowledge of elite level footballers.


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