From Janet who teaches tango and the Alexander technique:
“Regarding what I’m calling red and white muscles: Think of a chicken—dark and white meat. Dark is the legs and thighs, chickens can walk around all day.
Those are the deep muscles that support our bones. The “white” is the wings and breast. Chickens can fly in spurts but not very far or for very long. Those are our larger muscles on the outside (generally) of our bodies that we use for larger movements. These muscle groups can be trained to take over the work of the other, but, generally we desire to enhance the strength of the red muscles because they have greater strength in the long run. We use all these groups all day. What gets us in trouble (one thing) is using the white muscles to support the bones instead of the letting the red muscles do that. Using the white muscles to do the work of the red causes the red to lose tone and, therefore, strength. The good news is that that is reversible. Over use of white muscles is tension and lack of flexibility. We are not able to move smoothly and easily.”