Hi
I have never travelled with gels and just get them at the Expo. HMRC website should answer your query if you are worried about your gels of choice.
However when travelling from the UK I have never had my checked-in luggage opened. On three occasions travelling from USA I have had my checked-in luggage opened and searched. If searched on arrival in USA I doubt there would be much interest in your gels.
Providing you use the padlocks with a red motif and white cross the worst that would happen is the gels could be removed and the padlocks reinstated. Lets face it many people will put shaving gel, shampoo, cream or vaseline in their case. None of these items were removed from my checked-in luggage on leaving USA.
Best of luck with your race (NYC Marathon?).