When therapists and health care professionals talk about “flexion”, they are referring to the bending of a joint or the movement toward the front of the body.
In the photo above, most every aspect of the model’s body is flexed (except for the elbow and hands-even the shoulders are flexed because they have moved toward the front of the body rather than behind the body).
Understanding the difference between flexion and extension will help you follow along when a healthcare provider such as a doctor or physical therapist is outlining an exercise regimen or speaking of how a body part moves.
Anatomical flexion isn’t to be confused with body building flexion although the two terms can actually be used is the same sentence or situation. When body builders (or those influenced by them) talking about flexing, they are generally referring to tensing up their muscles to show their size and definition. We are speaking strictly of movement in this context.
When you make a fist, you’re flexing your fingers. When your knee bends, it is moving into flexion. When you move your chin to your chest, you are flexing your neck. When you do a crunch or sit up, you are flexing your trunk.
Flexion is the opposite of extension.