First I will set context: I am going to be 44 soon. I train in BJJ between 3 to 4 times a week consistently. We are Leglock friendly at our club, but we don't go crazy with it. I am also into HIIT bodyweight exercise somewhat. In the summer months I an into some extreme sports that are hard on the knees, namely Wakeboarding, but also skateboarding and BMX. I have been training JJ for 4.5 years now, and I have been lifting for about 3 years. I am lean and strong and my legs have always been a strong point for me. I've never had issues beside temporary JJ related injuries (Popped/Stretched LCL on both knees, once each) that have healed without any evident long term effects. Just recently I am feeling dull, constant aching inside my knee joints, and they just kinda feel loose. When I walk. When I relax my leg and flop it around. When I put load on it and turn. It feels like the joint as a whole is just becoming looser. I know there are a lot of different tendons and ligaments that hold it all together, but I can't imagine them all just starting to fail or wear out at the same time. So the question is, are there any ways to "tighten up" the knee joint with particular exercises?