Active vs Passive range of motion gives great insight to how much at risk of injury someone is in that range.

Active ROM is how far your joint can move on its own (you do it yourself and have full control of, say, your leg in a straight leg raise). 

Passive ROM is how far your joint can move in a relaxed state with assistance (stretching, using momentum, or someone else helping you).

Ideally, you want to have the Active and Passive ROM as close as possible to prevent injuries (meaning, all ranges of motion are able to be controlled by you).

The bigger the gap between active and passive, the bigger the chance of injury.

In this video, I demonstrate a leg swing using momentum first (passive ROM), and then I hold it at end range (active ROM). 

Check your flexibility to see how much of that range is active. Whatever that gap is, work on closing that gap, and you’ll be doing yourself a huge favor!