Who said my knees are not fully functional I am going mountain biking this weekend I went snowboarding this winter
If your knees are fully functional, why not go all out and do whatever it takes to add muscle, including heavy squats, leg presses, lunges and seated knee extensions, etc?
Not having any metalwork in my knees, I assumed that folks who do, like my wife did, are advised to take precautions.
As a result of osteoarthritis, my wife had both knees replaced (knee arthroplasty) several years apart. This was a long while ago and no doubt there are advancements in the procedures and prosthetics. In her case, there was both muscle atrophy and over a long time bone atrophy. Knee implants last about 15 to 20 years.
Although I don't have any metal in my knee, I had arthroscopic surgery in my right knee for a torn meniscus. It doesn't give me much trouble anymore, it took a long time and many physical therapy sessions for it be relatively normal. The day I had the surgery I was sent home on crutches with instructions not to put weight on that leg for a month, my wife fell and needed help getting up, which required me to use my right leg. No doubt this lengthened the recovery time.
