(The knee joint is like a hinge on a single hinged door; it works well if the hinge is strong and you don't habitually twist the door our of alignment when you use it).
#006 Mat class: hurdles stretches and advice…
(The knee joint is like a hinge on a single hinged door; it works well if the hinge is strong and you don't habitually twist the door our of alignment when you use it).