1. The problem statement, all variables and given/known data When I push my belly forward, a force is exerted on my belly by my muscles. So there will be a reaction force acting on the muscles right? But eventually it has a net forward force. So if we treat the belly as one object (muscle fat everything in the belly) then where is the reaction force from my belly swinging forward. 2. Relevant equations None 3. The attempt at a solution I'm thinking it should be the air behind it. Since my force is forwards, so the object directly behind my forward force is air? But I'm not very sure about this though. Thanks for the help physicsforums!