This is probably one of the more sciency editions of The Art of Movement, and I hope I am able to convey the message of this law to you in an effective way - however if you finish reading with more questions than answers please get in touch and ‘fire away’ (hopefully you get the pun by the end). Before we discuss the ‘all or none’ law, you must first understand what a motor unit is. A motor unit is composed of a single motor neuron that innervates all of the muscle fibres connected to it. Don’t let the terminology scare you, essentially we are just talking about a pathway which sends messages to your muscles and tells them to switch on!