Hi - Katrina from WorldNomads.com here. World Nomads Travel Insurance policies do differ, depending on your country of residence (which you don't mention here), however, most of our policies do not cover you to take part in races or any sporting events as a professional.
You can take a look at all of the recreational adventure sports and activities World Nomads travel insurance covers here - http://worldnomads.com/a2z.aspx
Do contact our Customer Services team by phone or email if you'd like to clarify exactly which activities and sports you'd like to do while travelling and whether you are covered ( or not) - http://www.worldnomads.com/contactus.aspx about 7 years ago
Be careful to check the sports covered in the travel insurance you buy, even if it's a sports specific one.
I went on a rugby tour abroad and one of the guys realised that rugby wasn't one of the sports covered in his insurance - you had to pay extra.
The same goes skiing - you will need a winter sports coverage. about 7 years ago