I compete in Endurance and my one mare who is 13 has been using a running martingale since she was 4. My other horses use regular martingales. We use them to help keep them traveling straight and not all strung out. A horse moving down the trail all strung out for 50 to 100 miles is bound to come up sore at some point. I think you should make the decision. If you think he needs the martingale then use it on trail if you just want to use it while training then use it like that. You know the horse best so at the end of the day it's your call. Have fun and be safe!