Moderate to severe osteoarthritis affects more than 22 million American adults between the ages of 25 and 74 and knee osteoarthritis (OA) can lead to disability in daily activities. Weakness in the quadriceps can be a risk factor for knee OA, but it may be the easiest one to prevent. Previous studies have rarely investigated whether quads strengthening exercises prevent or slow progression of knee OA or changes that are visible in X-rays. None have used the highly standardized x-ray procedures employed in a new study published in the October 2006 issue of Arthritis Care & Research (http://www.interscience.wiley.com/journal/arthritiscare), which examined the effects of strength training on the incidence and progression of knee OA in older adults.
Led by Alan E. Mikesky, PhD, of Indiana University and Purdue University in Indianapolis, IN, researchers conducted a study of 221 patients divided into 4 groups (OA/pain, OA/no pain, no OA/pain, no OA/no pain) that were then randomly assigned to either a strength training (ST) program or a range-of-motion (ROM) regimen for 30 months. Patients initially trained at a fitness center twice a week and at home once a week; the sessions at the fitness center were gradually decreased until patients were doing all of the workouts at home after the first year. The ST program included upper-body exercises, but was focused on resistance training for the lower-body. The ROM exercises consisted of simple movement exercises without weights. Strength was measured and X-rays were taken at the beginning of the study and at 30 months. The severity of OA features on the X-rays was rated independently by two different readers who didn't know to which group each patient belonged. In addition, patients were asked to return to the fitness center for strength testing and assessment of pain and function every 6 months after the first year. Of the 221 patients, 67 did not complete the exercise program, mostly because of time and travel constraints; 174 patients were evaluated at 30 months.
The results showed that patients in both groups lost lower-extremity strength over 30 months, but the rate of loss was slower with ST than with ROM. In patients with OA at the beginning of the study, the average loss of joint space width as seen on X-rays was 37% less in the ST group than in the ROM group, although this was not considered to be significant. However, progression of joint space narrowing occurred less often in the ST group. In addition, neither group showed a decrease in knee pain, although this is not particularly surprising in light of the fact that half of the patients did not have any knee pain when the study began. Patients in the ST group did begin to show better function during the last six months of the trial.
The researchers note that resistance exercise has consistently been shown to maintain or increase muscle mass, as well as improve strength. "In light of several previous positive studies in this area, the present study's failure to demonstrate gains in isokinetic quadriceps strength in the ST group is difficult to explain," the authors state. One explanation might be that adherence to the exercise programs was only moderate during the first year, although it increased slightly during the remainder of the study. The fact that patients showed gains in isotonic strength (i.e. weight lifted with exercise machines such as leg presses) but not isokinetic strength (i.e. the speed at which weight is lifted) may have to do with the fact that isotonic strength was measured in a way that closely resembled the exercises patients were familiar with.
Despite the lack of gains in isokinetic strength, a beneficial effect of strength training, namely less progressive joint space narrowing in the ST group, was suggested in the X-ray results. However, negative effects were also noted: in knees that were normal at the beginning of the study, joint space narrowing was more common in the ST group than the ROM group. The authors do not believe, however, that strength training is harmful for adults without knee OA, citing other studies that have shown benefits from these types of exercises. "In any event," they conclude, "this finding requires confirmation in future trials of resistance exercise programs for older adults, which should include serial standardized radiographic or MRI examination to monitor possible adverse effects of lower-extremity resistance on articular cartilage in the knee."
Contact: Amy Molnar
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