At the Champions League final there is likely to be evidence of faith, with players making the sign of the cross and other religious gestures. But does belief really boost sporting performance, asks Matthew Syed.
All eyes will be on Lionel Messi, the world's greatest footballer, when he walks out with Barcelona in the Champions League final. If you watch carefully, you may see him crossing himself as he strides onto the pitch.
On the opposing side, Manchester United striker Javier Hernandez has been known to pray on the pitch.
Messi and Hernandez are not the only footballers to reveal their beliefs during the pursuit of their sport. Real Madrid star Kaka has often talked about his faith, praying on the pitch and thanking God for his rapid recovery from a broken back.
Other sportsmen, from Muhammad Ali to Jonathan Edwards, the triple jumper, have also spoken about the power of faith. They believe in different theologies, but all would assert they have benefited from their convictions. As Ali put it in the build-up to his clash with George Foreman in 1974: "How can I lose with Allah on my side?"
Atheists will regard the idea that religion can make a difference to outcomes in sport as fanciful. But it is possible to put aside the issue of whether or not God exists and just examine the impact of faith on performance.
This is what Jeong-Keun Park of Seoul University did in 2000 by studying the performances of Korean athletes. He found that prayer was not only a key factor in coping with anxiety but also in attaining peak performance.
A quote from a participant in Park's study encapsulates the findings: "I always prepared my game with prayer. I committed all things to God, without worry. These prayers make me calmer and more secure and I forget the fear of losing. It resulted in good play."
This echoes extraordinary research about the power of faith from the world of medicine. In the 1960s, a series of studies found that heart disease is far less common among the religious than in the general population, even after controlling for different lifestyles. Later studies extended this finding, including a paper in 1996 which found that mortality rates in secular kibbutzim are nearly twice that of their religious counterparts.
It seemed that religious beliefs conferred real health benefits.
How is this possible? You can look for answers in one of the most perplexing of all psychological mysteries - the placebo effect, a phenomenon that has transfixed doctors since Theodor Kocker, a Swiss surgeon, performed 1,600 operations without anaesthesia in Berne in the 1890s.
Kocker's patients were told that anaesthesia had been administered and were able to endure surgery without even clenching their teeth, despite the fact that they had nothing beyond saltwater running through their veins.
In recent years, the placebo effect has been found to extend way beyond pain relief. It can cure ulcers, combat nausea and much else besides. It can also boost concentration, so long as the pill is dispensed in the right colour. Pink placebos, it turns out, have better concentration-boosting qualities than blue ones.
All of which hints at how the placebo effect works. Its power has nothing to do with the pharmacology of the drug (which is, by definition, non-existent); rather, its effect derives from the power of belief in the drug.
But this belief is not created out of nowhere, it is manufactured within a context. Anything that imbues the treatment with greater authenticity will strengthen belief. Colour, for example, is strongly connected in certain cultures with certain types of effect: red is buzzy, white is soothing. Drug companies play on these meanings. Stimulant medication tends to come in red or orange, antidepressants in white, and so on.
The placebo effect provides one possible explanation as to why those with religious beliefs have better health outcomes. Instead of a belief in the efficacy of sugar pills, patients have a belief in the healing power of God. And it is not just Christians who have better outcomes, but also those who hold different beliefs, such as Muslims. It would seem that it is not the content, but the strength of belief that matters.
As Anne Harrington, Professor of Medical History at Harvard University, puts it: "There is an innate capacity for our bodies to bring into being, to the best of their ability, the optimistic scenarios in which we fervently believe".
The results from the study of South Korean athletes have been replicated again and again, and across religious boundaries. The belief that a higher power is guiding one's performance seems to boost performance and remove doubt, something which can help sports people just as much as it helps patients.
Even away from faith, there are examples where belief can appear to change outcomes in sport. England midfielder Paul Ince used to leave it until the last moment to put his shirt on. Goalkeeper Mark Schwarzer has worn the same shin pads since he was 16. Nani, the Manchester United winger, plays with his socks the wrong way round.
Of course, these superstitions have little relevance to performance - unless you really believe they do. As Edwards, who lost his faith after retirement, put it: "Any belief can have powerful effects, so long as it is held with sufficient conviction".
All of which suggests that religious conviction really can boost performance, but only if you truly believe.
Matthew Syed is the author of Bounce: The Myth of Talent and the Power of Practice