most sports travel insurance policies will cover amateurs for competing in events like marathons - they won't cover you if you are a professional athlete. and many exclude the most hazardous sports like parachuting, climbing Everest etc.
if you partake in a number of sports outside the UK that insurers deem "hazardous" - and I include here things like marathons, skiing, cycling, triathlon, mountain biking, mountaineering etc plus those that many do on holiday as a fun day like jet skiing, white water rafting,etc, then you really should consider an annual sports cover policy as it saves a huge amount of faffing come travel time. many of these polcies will also include general holiday cover for illness, repatriation, baggage loss etc.
we're with Dogtag and have previously used Snowcard but there are others such as the BMC (British Mountaineering Council who offer wider ranging insurance), Sports Cover Direct etc. our annual policy is about £200 for 2 of us and covers us for extreme conditions such as off piste helicopter rescue while skiing without a guide - that's about extreme a rescue as you would need! well worth the comfort factor of knowing it's there.
Edited: 25/09/2012 at 09:16