When the muscle activates or bunches up, it pulls on the tendon. Tendons attach muscles to bones. The tendon pulls the bone, making it move. To relax the muscle, your nervous system sends another message.
To generate a movement, agonist muscles must physically be arranged so that they cross a joint by way of the tendon. The contraction will move limbs associated with that joint. In this sense, the bone acts as a lever with the attached muscle fiber's contraction, driving movement.
