"It would be a mistake, however, to conclude that such muscles play no part whatsoever. Every muscle plays a part, in the correct proportion, of course."

At the correct time.

There is an important difference between using opposing muscles in proportional opposition to position a joint, and release the joint completely to allow it to respond to body inertia.

Both have their time and place in dancing. But the free movements can be both the hardest to learn and the most rewarding in the capability they deliver when achieved in their proper context.

Muscle activation is something that can be electrically measured with a trio of taped on electrodes - most dramatically with equipment which converts motor nerve activation to sound. A person moving a limb with intention can easily be distinguished from a person relaxing their limb and allowing it to be moved by a force external to its musculature.

That is a great question! As a dance coach and judge , I can certainly answer such a question.

Steps taken with heal leads are typically ballroom ( International Standard) and smooth ( American/social style). Latin dances are not typically danced with heal leads, with the exception of Paso.
What is a heal lead?? It is when a dancer takes a forward step and the first part of the foot that so.mes in contact with the floor is the heal. This means the ball of the foot has to be lifted off the floor at some point.
A side step or back step can not be taken with a heal lead, since on side steps they are either taken on the inside edge of foot, or ball/toe of foot. In dancers where there is elevation changes, then the first forward step coming out of a the lowest elevation would be taken with a heal lead. Eg. In waltz there are 3 beats, where the 1st beat is the lowest in elevation and that woul dbe taken with a heal lead , the second and third steps have elevations, and a dancer to create elevation to the max have to have their weight on their toes.It is very incorrect to have an elevated position with weight on toes and then take the next forward step with heal....very common mistake with beginners, since you would have to lower your elevation first with the supporting foot BEFORE you can take a step forward with a heal . Latin dancing typically involves having the balls of the feet in contact with the floor at all times with very few exceptions, meaning that you can not take a heal lead, since to do so, it would require you to lift the ball of the foot from contact with the floor.

Hope this helps, happy dancing ! Giorgio Argentini