If your friends are pressuring you frequently, put a stop to it by saying “no”. You don’t need to be aggressive or confrontational.
You can simply say: “I’m not really into that” or “I’d rather do something else”. If you’re scared of saying “no”, try practicing what you’re going to say at home first.
Good friends won’t ask you to explain or apologise for not wanting to do something. However, if you feel the need to have an excuse, think of something you can say before meeting them.
Something like, “No thanks, I’m training for an athletics competition next week” or “I’m trying to be really healthy this month” might work.