Video: World Cup
Editorial: Soccer hits the heights
Online game: Score goals at different altitudes, if you can, with Haake and Choppin's shot simulator (requires Microsoft Silverlight)
FEBRUARY 2007. Brazilian football team Flamengo are playing a South American cup match in Bolivia. Their opponents, Real Potosi, are based in the high Andes and the stadium is nearly 4000 metres above sea level. In lashing rain, Flamengo fall 2-0 behind. Many of their players need bottled oxygen to alleviate the effects of altitude. Though they eventually fight back for a 2-2 draw, Flamengo announce after the game that they will no longer play matches at altitude.
So began football's "high altitude controversy". Flamengo's case was taken up by the Brazilian Football Confederation, which complained to the world governing body FIFA that venues in the high Andes were not suitable for football. In May 2007, FIFA ruled that "in the interests of player health", international matches could no longer be played above 2500 metres.
If Brazil thought that meant victory, they were not reckoning on a comeback by Bolivia, Ecuador and Colombia, who complained to FIFA that this would put a stop to international matches in their national stadiums. In response, FIFA suspended the ban pending further studies.
Fast-forward to June 2010 and altitude is again an issue in football. The World Cup in South Africa will be the first for 24 years to stage games at venues significantly above sea level. The main stadium, Soccer City in Johannesburg, is at 1701 metres. That's not quite the high Andes, but it is still high enough to have an effect. Six other venues are at altitude (see map). Will it have a bearing on the tournament?
In the wake of the South American controversy, FIFA invited leading medical scientists to a conference in its home city of Zurich, Switzerland, in October 2007 to discuss what was known about the effects of altitude on football. The delegates quickly established that there are few well-controlled studies on football at altitude, so they would have to make inferences from research on other sports, including running, skiing and climbing.
The first thing they looked at was physical performance. They concluded that below 500 metres there are no effects. Above 500 metres, negative effects such as increased heart rate, breathlessness and reduced stamina become noticeable and get progressively worse the higher you go - though some people are more badly affected than others. At 2000 metres altitude sickness becomes a problem and acclimatisation is essential. Above 3000 metres there are substantial hits on performance.
The physiological effects of altitude are mainly caused by a reduction in the amount of oxygen in the air, which in turn limits oxygen levels in the blood. The resulting decrease in an individual's physical performance can be quantified by a measure called VO2max - the maximum rate of oxygen uptake in litres per minute per kilogram.
Research on endurance athletes has shown that above 300 metres, VO2max falls by around 6 per cent for each 1000 metres in elevation, while the time before exhaustion sets in drops by around 14 per cent per 1000 metres (European Journal of Applied Physiology, vol 96, p 404).
The standard way of minimising this decline in performance is a few days of acclimatisation. The FIFA team recommends spending three to five days at altitude, although it is never possible to recover full sea-level fitness levels in this way. Even Bolivian footballers who live at altitudes of 3600 metres have a VO2max around 12 per cent lower than footballers living at sea level (Journal of Exercise Physiology, vol 3, p 29).
So are the physiological effects of altitude likely to skew the results of matches at the World Cup? Probably not. None of the venues is above 2000 metres, and most of the 32 teams will be living at altitude during the tournament. Those that are not are certain to use altitude chambers to prepare.
Flight of the ball
There is, however, a wild card. Some researchers at the meeting noted that there are reports of athletes who are acclimatised to altitude suffering a decline in performance after suddenly descending to sea level. This effect may put them at a corresponding disadvantage when they come down to play a team acclimatised to sea level (Scandinavian Journal of Medicine & Science in Sports, vol 18 (supplement 1), p 85). This could influence the latter stages of the tournament, as both semi-finals will be played at sea level between a team that won its quarter final at altitude and a team that won at sea level.
Athletes acclimatised to altitude can suffer a drop in performance after suddenly descending to sea levelIt's not just physical performance that is affected. The FIFA team also concluded that altitude is likely to alter the aerodynamics of the ball in a way that could catch players out.
The key to this is the reduced density of the atmosphere, which affects how fast the ball moves through the air and also the bend of a spinning ball. Every 1000 metres increase in altitude reduces atmospheric pressure - and hence the density of the air - by about 11 per cent (though the precise formula is more complicated than this). Other things being equal, Johannesburg has an atmospheric pressure around 81 per cent that of Cape Town.
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Sunday, 6 June 2010
Feeling the pressure: The World Cup's altitude factor
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