Decreases in cartilage that protects bone surfaces leads to joint pain and arthritis.  Frank Roemer and colleagues from Boston University Medical School found that obese people over 50 showed accelerated cartilage loss in the knee.  They measured cartilage changes over 30 months.  One unit increase in body mass index resulted in an 11 percent decrease in cartilage thickness.  They suggested that weight loss was the best way to prevent cartilage loss.  Other studies found that weight training prevents cartilage loss and arthritis.  Building strong muscles helps support the joints and prevents excessive stress on cartilage cells.