I heard from a good friend that if I am on glucosamine (which I am for knee joint pain), that if I lift heavy doing Squats or Sled, then I will be damaging the bursa sack in this area of my knees and will do more damage than good. His explanation was that the glucosamine some how weakens the bursa sack, thus basically crushing it using heavy weights on the affected area. Is this true and if it is then can you only use glucosamine during a recovery period, during which you should stay off of lifting all together??