Instructions
Load "GMod" and enter a private game or a hosted game server.
Press "Q" to open the creation menu and select to spawn a ragdoll, or any other item you want, from the list of available props.
Place the ragdoll down somewhere in the game. Open the creation menu again and select the Muscle tool, under the Constraint tools list, and choose a keypad number to activate the muscle.
Shoot the Muscle tool on the ragdoll's body part that you want to animate. Then shoot the Muscle tool again to a different part of the ragdoll. This will link the two spots together.
Press the keypad number you selected in step three to activate the ragdoll's animation. The two tethered locations will expand and contract to simulate a muscle. Press the keypad number again to deactivate the muscle.