Mechanical Unweighting Effects on Treadmill Exercise and Pain in Elderly People With Osteoarthritis of the Knee

Kathleen Kline Mangione, Kenneth Axen, Francois Haas

Summary by Patty Davis, MS, Mobility Research, 28 March 1997

Osteoarthritis of the knee joint is a very debilitating disease. The intense joint stiffness, pain and decreased range of motion often makes ambulation difficult. It is often times, much more difficult for the osteoarthritic individual to complete many of the daily tasks of life; social and otherwise. The corresponding decrease in activity level often has an adverse effect on the muscular strength and endurance, cardiovascular conditioning, functional ability and the emotional state of the individual. The benefits of exercise to this population are tremendous. In an attempt to keep those individuals with osteoarthritic knees active, aquatherapy protocols, which decrease the amount of weight bearing load on the knees, have been prescribed. While this approach is thought to have benefit to the osteoarthritic population, there has been very little, if any, research documenting the benefits of aquatic exercise. In a study looking at the "Efficacy of physical conditioning exercise in patients with rheumatoid arthritis and osteoarthritis", Minor et al. found decreases in pain and depression levels, and an increase in the functional ability of the deconditioned population. It was, however thought that even though pain levels decreased, there was still a significant amount of pain to force the early termination of the exercise sessions. The exercise sessions were, therefore, not of sufficient duration and intensity to elicit significant cardiovascular conditioning effect. The purpose of this study was, therefore, to look at the effects of a partial weight bearing treadmill exercise protocol on knee pain and cardiovascular response in an osteoarthritic population.

4 men and 23 women, with an average age of 68 years, were used as subjects for the study. All of the subjects were diagnosed with osteoarthritis for an average of 12 years, and had no evidence of other rheumatic disease, neurological or cardiopulmonary conditions which would inhibit safe treadmill exercise, or the use of medication related to hypertension, cardiovascular or pulmonary disease. A Zuni Exercise System was used at the unweighting device, and utilized a harness suspended from a tensiometer to precisely adjust the weight bearing load. Oxygen consumption and heart rate data was monitored and recorded throughout the testing. Perceived pain data was measured with a visual analog scale which ranged from 0 mm (pain free) to 100 mm (maximal imaginable pain). Three graded submaximal treadmill stress test trials were complete by each subject. The three trial of 0%, 20% and 40% body weight supported were completed in random order, with the subjects having no knowledge of the amount of support provided by the device during each exercise session. The Naughton protocol used for the stress test consisted of three minute stages where speed remained constant and elevation was raised 3.5% per stage. VO2 and heart rate data was collected in 30 second increments, while the subject's perceived knee pain level was measured during the last 30 seconds of each stage.

Analysis of the results of the study found that, as expected, VO2 and heart rate levels closely reflected the change in weight bearing load. At 0% and 40% body weight support, VO2 and heart rate levels reached their highest and lowest levels respectively. The American College of Sports Medicine's exercise effectiveness guidelines outline that for cardiovascular exercise to effect significant change in condition state, an individual must reach between 55%-90% of the age-predicted maximum heart rate. When comparing the data collected to the ACSM guidelines, it was found that 27 of the subjects reached the target heart rate of 55%-90% of maximum values when exercising at 0% and 20% body weight support. When exercising at 40% body weight support, 25 of the 27 subjects reached the ACSM target heart rate guidelines. Also, when exercising at the 20% and 40% BWS, the subjects on average, exercised for longer periods of time. When looking at the perceived knee pain data, it was found that decreased weight bearing had no significant effect on pain levels during submaximal stress testing conditions, with a significant amount of treadmill elevation built into the test protocol.

The results of this study are promising in that they provide support to the usefulness and effectiveness of partial weight bearing exercise protocols for various populations. Partial weight bearing exercise provides significant oxygen consumption demands to stimulate a cardiovascular conditioning effect. The benefits are two fold in that a cardiovascular conditioning effect is achieved in an environment that is free from falls. The individual's are safely supported during their cardiovascular exercise, which has the potential to have a significant impact on the geriatric community. The fact that this particular partial weight bearing protocol did not decrease knee pain level during a graded submaximal treadmill test is important in that it brings to light new research question such as: Does partial weight bearing exercise facilitate a decrease in pain levels when treadmill walking at submaximal levels, with 0% elevation? Or would a partial weight bearing exercise protocol provide a safer, more effective long term exercise environment for osteoarthritic and/or geriatric populations? Partial weight bearing devices offer new and exciting avenues for the exercise and rehabilitation of elderly and/or disabled populations. The promise of partial weight bearing exercise and rehabilitation must be explored to determine the most appropriate partial weight bearing exercise protocol parameters and to realize to vast scope of its impact.