No, a Knee Locker is not a locker at the gym to keep you knees in. It is someone who habitually locks their knees when standing.
What does standing with locked knees actually mean? More importantly, why should you care?
I differentiate between standing with knees (1) locked (2) balanced or (3) bent.
Standing with bent knees over time is tiring because you have to work to keep the bent joint stable.
Standing with locked knees is also a waste of energy as you habitually contract muscles in the quadriceps (front of your upper legs) to push your knees backward as far as they will go.
More importantly to our recent discussion of standing is that standing with locked knees also often results in you pushing your hip joints forward in response.
Notice that there is not a big visual difference between the locked knees and the balanced knees. If you find that you are locking your knees, don’t bend them but just stop locking your knees. You will probably notice a subtle change but not a huge change. It may just be a sensation of not tightening in your legs so much.
Standing on balanced knees allows the weight to transfer down through the upper leg bones, through the knee joint and down through the lower legs bones, the ankles the arch of the foot and into the floor. You can think of locking the knees as blocking that easy flow down through the legs.
So if you have noticed over the past few weeks that you do tend to park your hip joints forward another way to work on it is to notice if you lock your knees when you are standing and intervene by practicing not locking your knees.
Here is a great blog post by a physical therapist that talks about this very subject. It gives you a simple exercise to practice becoming more aware of the knee locking habit.