|If it looks like a duck, and went to medical school...|
There are a few simple ways to take care of general anterior knee pain; the type of knee pain most people are talking about when they tell you their knee hurts. They revolve around being weak and being tight; the two things that cause most of our joint pains.
In terms of strength, its either not enough overall strength, or its an imbalance caused by improper exercise. A lot of recreational, even competitive, athletes will only play their sport and not do the proper strength and conditioning to go along with it. This results in a dominance in certain muscle groups; in terms of volleyball players we see a huge reliance on the quadriceps for propulsion and for landing. They want to do everything on their toes to incorporate as much quadriceps as possible. This leads to weak hamstrings and glutes, which causes poor hip extension and increases pressure on the patello-femoral joint. Fix it by deadlifting! To take this a step further, you can get an imbalance within the quadriceps muscle. If your Vastus Lateralis (the big muscle on the outside of your thigh) is much stronger than your Vastus Medialis Oblique (the little tear-drop just above your knee) then you can suffer from a sub-luxating patella; that is, a kneecap that doesn't track properly. One of the best ways to fix this imbalance is to get off the leg press and leg extension and start lunging and squatting.
Now, some people may be doing these exercises and still be experiencing knee pain. There are some other causes, as well. One of the muscles that plays a huge role in control of the hips is the Glute Medius. One of the easiest ways to check the function of a client's glute medius is by watching them squat; if they experience valgum stress on the knees (knee caving) during a squat. There are a few simple exercises to help with this; squatting with a band around the knees, sitting with a band around the knees and pressing out, or X-band walks.
These will also help with instability issues when performing a lunge. Weird how its all connected, no? Instability/weakness at the hip joint causes pain at the knee by the transfer of stress. Your body simple shoots the stress down the muscles, and suddenly your knees hurt.
Those are the big muscular deficiencies that can cause general knee pain. The other big thing is soft tissue quality; flexibility and mobility. If you move like crap, you're gonna feel like crap. Hip mobility and ankle mobility are going to play a HUGE role in the way your knees feel. I know you can't change the fact that you sit for 8 hours at work, but you can do something to help fix it. Foam roll every day; do a dynamic warm-up; run through some mobility drills. It may add 20 minutes to your workout, but your body will thank you down the road.
Foam rolling your IT bands is one of the quickest ways to help alleviate some knee pain. When your IT Band (Iliotibial band) or TFL (Tensor Fascia Latae) get tight, they cause your upper legs to pull/rotate in an outward manner. This causes your patella to get off track and will really disrupt proper function at the knees. Roll/stretch out your hips and legs consistently, and it won't be long before you are back to moving the way nature intended.
Of course, these are things you can do in the gym to help get your knees healthy. In the event that your knee pain is severe or acute, you should probably go talk to a doctor about it.
Now go lift something heavy (but do some dynamic mobility drills first!)