Broudly speaking, extensibility refers to the ability of muscles to lengthen. Flexibility refers to the range of motion a muscle will allow a joint. Mobility refers to the full range of motion afforded a joint by all attached tissue – muscles, ligaments, tendons and fascia.
Kelly Starrett, PhD Physiotherapist, , Founder of Mobility WOD, Owner of San Francisco CrossFit and all-around mobility superhero and nice guy here at Crossfit Copenhagen to help with this video on how to assist mobility for overhead squats.
If overhead squats (or regular squats or any lifts requiring overhead position) are uncomfortable for you then definitely try these drills out. Best to get on to this before you have a rotator cuff issue!
After that, have a look at PhD physio Kelly Starrett’s book, Becoming a Supple Leopard, for more great mobilization tips.