Unfortunately, training hard and participating in sports can be hard on the joints, particular the knees. Products that promote joint health are obviously popular among athletes, particularly older athletes. However, it's questionable how well any of these products and supplements really work.
A couple of years ago I was turned onto a fairly new joint health supplement, glycine. Glycine is definitely not new but its benefits for joint related conditions are not all that well known. Glycine is a non-essential amino acid that is a precursor to collagen production. Collagen is an essential component to connective tissue such as cartilage, tendons, and skin. Being an amino acid it's naturally present in the diet. I don't remember how I first heard about it but a few yrs back I read some feedback from a person saying he had taken it for a couple of months and actually had MRI evidence of a cartilage lesion healing. I then saw a couple of positive studies on it for arthritis, so I decided to try it.
I was pleasantly surprised. I'd used glucosamine for years and can't say I ever noticed anything positive or negative from it. That's ok because the research on glucosamines ability to rebuild cartilage is sketchy - the positive science on it shows that at best it helps maintain existing cartilage. Yet, within a few days of supplementing with 10 grams of glycine per day I could "feel" a difference. My stiff joints weren't so stiff and the difference was quite noticeable. In addition to being a precursor for collagen (and thus cartilage), glycine also has direct positive benefits on inflammation present in joint related conditions.
I've since turned many others onto glycine and most of them reported significant positive benefits. Glycine is also dirt cheap. A 500 gram bottle is less than 10 bucks. Supplementation with glycine may also do positive things for the skin and taken before bed may also improve sleep quality. It also may benefit non-cartilage related joint conditions such as tendonitis. If you have sore, achy joints, particularly with clicking and grinding (symptoms of cartilage damage), definitely give it a shot, - dosage is 5 grams twice a day, about 2 teaspoonfuls per day. You can also get it via supplementing with gelatin, but straight glycine is more economical.
Additionally, if you have a joint pain issue you probably also have various movement impairments contributing to your pain. If you have stubborn chronic knee pain and want to figure out how to address it take a look at Anthony Mychal's "Guide to Chronic Knee Pain"