But the USA Cycling test can't quantify an athlete's emotional readiness to re-enter the sport after a head injury.
Brain injury in sport is something most of us associate with boxing.
Last week, the Swiss Football Association told BBC Sport that Djourou's injury was not as bad as first feared and that the player was confident of returning to action this month.
Kevin Guskiewicz, director of the University of North Carolina's Matthew Gfeller Sport-Related Traumatic Brain Injury Research Center, said the "vast majority" of kids playing in youth football leagues aren't going to have the type of exposure to injury NFL players have.
However, two years out of the sport, coupled with a knee injury sustained on a skiing trip three months before her announcement, have left Johnson with an uphill struggle to regain her shape and her world-beating status in time for London 2012.
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Football is the collision sport that carries the highest risk of injury to every bodily joint.
However, specialists told him last week that he had to quit the sport because of the risk of future injury.
Alpine skiiers "hold the notorious distinction of having among the highest rates of ACL injury of any activity or sport, " study authors wrote.
What the injury proves for certain though is that professional football is a brutal sport where a promising career can come to a crashing halt because of a devastating injury caused by even a moment of indecision.
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Part of what makes dogfighting so repulsive is the understanding that violence and injury cannot be removed from the sport.
"I'm delighted to name Gavin in our 22, he's had a long road back again from injury, " Holley told BBC Sport Wales.
The return of Thompson, 31, is even more pertinent after he was initially forced to retire from the sport in April 2007 with a serious neck injury.
Boer returned to the club as a player in October 2009 to ease an injury after two years out of the sport and stayed for the rest of the season.
The striker is widely regarded as one of the greatest footballers the sport has ever seen and, after being hampered by injury during his country's 1962 World Cup win, he was a key figure in Brazil's 1970 success.
Harrison divides most sport injuries into two main area -- traumatic where a frank injury has occurred (i.e. a fall while skiing) or overuse injuries where over time there has been wear and tear on the body.
Knowing the types of injuries common in your child's sport(s) can help you observe the early warning signs of injury, and where to look for them.
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For what would seem to be obvious reasons, teams do not want their star players, whom they have so much invested in, risking injury in a recreational setting, especially when it involves playing a sport other than the one they are paid to perform.
South African Nel has other injury worries and has named a panel of 22 for the trip to the Stade des Sport et de L'Armitie.
Clijsters won her only grand slam title at Flushing Meadows in 2005 but injury ruled out her defense the following year and in May 2007 she surprisingly walked away from the sport, saying she was tired of the injuries and lifestyle.
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