If the insurer offers several different policy levels you will usually be able to see which adventure sports are included at which level.
The policy will also have sections listing the activities insured if you pay for add-ons. For example, a winter sports travel insurance add-on might include skiing, snowboarding and so on. Other activity packs would include other sports – perhaps surfing and paintballing at the lower levels and bobsleigh and sledging at the higher ones. Insurers lists are usually very specific and cover all kinds of activities from abseiling, banana boating and camel riding to zorbing and zip lining.
Make sure everything you plan to do is on one of those lists, and look out for any exclusions. Insurance provider's activity lists should make clear what activities are and aren't included, and any limitations and conditions, for example, if it has to be done under the supervision of a qualified instructor, or there might be a maximum altitude for trekking, distance from shore for sailing or depth for diving.. With some providers, a variety of activities might be included if you do them once or twice, but excluded if they’re the main purpose of your trip.
Most travel insurance policies cover you as an amateur on a casual basis but won't cover professionals.
If you’re not sure, don’t just hope for the best. Contact the insurance provider and ask.