Although athletes can be studied under controlled conditions, this isn't quite the same as measuring them 'in vivo', when competing under pressure in tournament conditions. In the third film of his Engineering Sport series, Professor Steve Haake investigates how motion capture technologies, are being used to provide accurate measurements of athletes in the field. The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter