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The Arthritis, Diet, and Activity Promotion Trial (ADAPT), as described by Messier and colleagues in this issue of Arthritis & Rheumatism (1), is unique. It is the first large, randomized clinical trial assessing the symptomatic benefit of a facility-based dietary weight loss program, with or without the addition of supervised exercise classes, for individuals with knee osteoarthritis (OA). Furthermore, ADAPT specifically recruited only persons with knee OA who would be classified as either markedly overweight or obese. Because the proportion of overweight patients with knee OA is likely to increase with the rapidly growing prevalence of obesity in most parts of the world, the results of ADAPT should be of great interest to most clinicians.

Weight loss is considered an ongoing treatment priority for overweight persons with knee OA (2, 3). However, this advice is based mostly on observational studies demonstrating an association between high body mass index (BMI) and the risk of incident knee OA (4), and the association between weight loss and a reduced risk of symptomatic disease in women (5). Although the results of 2 nonrandomized studies suggested the short-term symptomatic benefit of weight loss for overweight individuals with knee OA (6, 7), no large randomized controlled trials have been conducted to provide rigorous evidence for the benefit of weight loss as a therapeutic intervention.

In contrast, international guidelines recommending structured exercise for individuals with knee OA are supported by the positive results of several well-conducted randomized trials and a systematic review (8). However, none of these trials specifically targeted recruitment of overweight or obese people, nor could they provide a meaningful post hoc analysis of the results according to BMI. Therefore, ADAPT not only addresses dietary weight loss, but also addresses the question of whether attendance at exercise classes is advisable for sedentary obese persons and, importantly, if any achieved weight loss or symptomatic benefit is sustained beyond the time of participation in the initial intensive, mostly facility-based program.

Currently, clinicians may be reluctant to recommend either of these facility-based programs to their obese patients, being aware that each program requires a considerable commitment of time and financial resources by the patient, that weight loss or regular exercise is difficult to sustain for most people, and that strong evidence for symptomatic effectiveness, specifically for this particular subgroup of patients with knee OA, has not been available.

In ADAPT, 316 sedentary older persons with knee OA and a BMI of at least 28 kg/m2 were randomly assigned to a dietary weight loss program, exercise classes, a combination of both of these interventions, or a control group. However, the control allocation was not entirely “inactive,” because persons in the control group were required to attend 3 education classes that encouraged weight reduction and regular exercise, and they were contacted monthly by telephone for the remainder of the 18-month study period. The facility-based dietary weight loss program and exercise classes were lengthy, conducted 1–3 times per week over the first 4 months after recruitment. Thereafter, participants allocated to the exercise classes were permitted to continue until the end of the 18-month study period at facility-based classes or to make a transition to a home-based program (supported by regular monitoring telephone calls from the exercise leader). Participants allocated to the dietary weight loss program continued to attend monthly meetings and received monthly monitoring telephone calls and regular newsletters.

The main finding of ADAPT was that only the combination of the dietary weight loss program with the exercise classes resulted in significant long-term benefits in terms of self-reported pain and physical function as well as objective measures of physical performance for these overweight and obese subjects. In fact, only the combination of interventions achieved significant benefit (above control) for the stated main outcome of self-reported physical function. These findings deserve further discussion.

At baseline, ∼80% of participants in the study were not only overweight, but were markedly obese. The mean BMI of study participants was ∼34.2 kg/m2. The weight loss targeted by the dietary weight loss program was a modest 5%. The mean weight loss achieved and sustained over the 18-month period by participants allocated to the dietary weight loss program was 4.9%, while persons allocated to the combination of dietary weight loss and exercise classes achieved a mean weight loss of 5.7%. Interestingly, participants allocated to exercise classes alone achieved a weight loss of 3.7%. With such a modest weight loss targeted and achieved, most study participants would still be classified as obese at the end of the study. It should be very encouraging to both clinicians and obese patients that clinical benefit can be achieved from even relatively modest weight losses. However, it would appear that a fairly structured and ongoing facility-based program is required to achieve and sustain even such a modest weight loss, because the brief education program did not result in comparable weight losses. Further research is required to evaluate whether larger reductions in weight can be achieved and sustained with similar facility-based programs and whether greater weight loss is associated, in a dose-response relationship, with more than the modest symptomatic benefits demonstrated in ADAPT.

Recommending weight loss, apart from the overall general health benefits, has considerable face validity for obese people with symptomatic knee OA, because a weight loss would reduce the magnitude of knee joint loading. However, there are some concerns when weight loss is achieved only through dietary control. It is hypothesized that without concomitant lower limb exercise, weight loss may simply result in loss of lean body mass, compromising muscle strength. Muscles of the lower limb function to protect the knee from destructive impact loading. In fact, the results of a nonrandomized study suggest that loss of body fat is more closely associated with symptomatic benefit than is loss of body weight (9). Similarly, the results of ADAPT also demonstrate that the addition of regular exercise to a dietary weight loss program results in superior symptomatic benefit, as well as greater improvements in objective measures of physical function, compared with that achieved by the provision of a dietary weight loss program alone.

Although the modest weight loss achieved by participants allocated to active treatment in ADAPT may partly explain the mostly small symptomatic effects demonstrated (above those demonstrated in the control group), some study methodology factors may also be explanatory. Such factors, as offered by the authors, included the provision of a treatment of proven effectiveness (education classes and telephone monitoring) (10, 11) for the control group and the generally mild symptomatic disease reported by most participants at baseline, limiting the potential to demonstrate improvement. Use of concomitant analgesia may also be another factor responsible for attenuating treatment effect size. Although increasing the clinical relevance and generalizability of the study results, effective analgesia may partly explain the unexpectedly mild symptomatic disease reported by most participants at baseline. Participants were “instructed to continue all medications and other treatment as prescribed,” but information on usage was not reported. Future research should quantify the frequency of analgesic use for knee pain at both recruitment and followup outcome assessments. The benefit gained by each of the treatment programs could have been expressed as a reduced need for analgesics, an important positive and clinically relevant outcome.

The finding that provision of the exercise classes alone did not result in significant improvements in self-reported pain and physical function contradicts the results of most randomized trials (8). The content and intensity of the exercise program and the structural disease severity demonstrated by many participants at recruitment may have been responsible for this result. The greater part of the exercise classes appears to involve walking, targeting an exercise intensity range from a mild 50% maximum heart rate up to a more challenging 70% maximum heart rate. Participants, while not selected for symptom severity, were obese, and all were required to have a “sedentary activity pattern” (<20 minutes of formal exercise per week) during the 6 months prior to recruitment. Walking is a repetitive weight-bearing activity. It is conceivable that, for many of these previously sedentary and obese participants, lower limb muscle function would not provide sufficient protection against uncontrolled impact loading of the knee, particularly when muscle fatigue starts to play a role. In fact, the superiority of non–weight-bearing exercise, compared with walking, for obese women with knee OA has been reported in a recent nonrandomized study (6). It may be more advisable, particularly for obese patients, to limit weight-bearing exercise initially and focus on lower limb strengthening and to increase fitness through cycling on stationery bicycles, rather than walking. It is also conceivable that in obese patients, a higher level of aerobic exercise would be more easily achieved with non–weight-bearing cycling than with walking. Given the results of a recent study demonstrating a clear dose-response relationship between exercise intensity and weight/fat mass loss (12), participants allocated to the exercise classes may also have lost more weight if they were able to exercise at 70% maximum heart rate rather than 50% maximum heart rate.

Previous studies have demonstrated that severe radiographic disease is associated with decreased responsiveness to therapeutic exercise (7, 13), supporting the general recommendation that regular lower limb exercise is particularly indicated in early disease. It would appear from the presented data (see Table 5 in the article by Messier et al) that many ADAPT participants had severe radiographic disease at the time of recruitment, limiting their responsiveness to exercise. Although a comparison of different exercise regimens and patient characteristics associated with responsiveness to treatment was beyond the scope of ADAPT, exploration of these factors clearly warrants further research before exercise classes, unless accompanied by dietary weight loss programs, are incorrectly considered to be of little benefit for obese people with knee OA.

Apart from the inclusion of only overweight and obese participants and the random allocation to a dietary weight loss program, the ADAPT study is unique for another reason. The study was long-term, conducted over an 18-month period. With few exceptions (14, 15), most studies to date of facility-based therapeutic exercise have assessed only immediate short-term benefits. Those studies that did assess long-term sustainability usually did not have positive results (16), probably due to the lack of ongoing patient supervision or contact. Exercise and diet modifications are interventions that, except for a few exceptionally motivated patients, require ongoing access to either classes or at least advice or encouragement through telephone contact. The maintenance of improvements in self-reported physical function from the 6-month to the 18-month assessment for the active-treatment allocations was probably attained, because 60% of participants chose to continue participating in the facility-based exercise program throughout the study period, and those who made the transition to a home-based program after 4 months received regular telephone calls with advice from the exercise leader. Dietary weight loss was also closely monitored in a similar manner, with monthly meetings and telephone calls. Considering the participant burden involved in these 2 nonpharmacologic interventions and the previous sedentary activity pattern of all ADAPT participants, the adherence rate of ∼65% over the 18-month period was an extremely encouraging finding, comparable with long-term adherence rates reported for most pharmaceutical trials. Furthermore, the finding that ∼60% of those participants allocated to exercise classes chose to continue at the intensive facility-based program after the initial 4-month period suggests that such programs appeal to obese adults with symptomatic knee OA.

The results of the ADAPT study are important for clinicians and patients, because they provide evidence for significant, although modest, treatment effects of a dietary weight loss program combined with regular exercise classes for sedentary, overweight and obese individuals with knee OA. The reported treatment effects have probably been attenuated by allowing participants to modify their analgesic management, using an effective treatment as comparator, targeting only a modest weight loss, and by the suggested suboptimal content and intensity of the exercise classes. Further research is now clearly needed to explore whether more ambitious weight loss targets, differing the exercise class content, or increasing exercise intensity for this population will result in larger symptomatic benefits.

REFERENCES

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  2. REFERENCES
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