A pilot trial of interval versus continuous walking exercise on clinical outcomes and biomarkers in people with knee osteoarthritis

Osteoarthritis (OA) is a common disorder and cause of disability in the United States. The most common site of OA is the knee. Knee OA (KOA) leads to a sedentary life style due to low functional levels and pain. A sedentary life style increases health care utilization and leads to the development of multiple comorbidities such as cardiovascular disease (CVD). Aerobic exercise has been shown to decrease knee pain, improve function, and enhance fitness levels of people with KOA. The OA Research Society International (OARSI), the American College of Rheumatology, and the Ottawa Panel of KOA have recommended at least 30 minutes of aerobic exercise such as walking exercise above daily activity intensity levels 3-4 times/week to maintain a normal fitness level. However, people with KOA usually fail to meet these recommendations due to exacerbation of knee pain during exercise, the time commitment, fear of harmful effects of exercise, muscle fatigue, and loss of effective shock absorption. It has been reported that compliance with continuous walking (CW) exercise is less than 50%, and 20-39% of people with KOA drop out from walking exercise programs. Recent research has reported that interval walking (IW) exercise can increase compliance to exercise and decrease attrition rate in people with sedentary lifestyles, people with obesity and type 2 diabetes, and postmenopausal women, while better improving fitness level and walking time duration with less joint symptoms when compared to CW exercise. However, only two crossover studies are available that have reported exacerbation of knee pain in people with KOA after 30 and 45 minutes of CW exercise but not after the same amount of IW exercise. Up to date, there is no study examining the effect of prolonged IW exercise on pain and fitness compared to CW exercise in people with KOA. The objectives of this study were: 1) to identify the long-term effect of IW and CW exercise on compliance and pain in people with KOA; 2) to explore the effect of IW and CW exercise on the pain level of the subjects with KOA at the end of a 6-week program and after each session; 3) to quantify the effect of IW and CW on the fitness level and selected risk factors of CVD in people with KOA; 4) to explore the effects of IW and CW exercise on select inflammatory biomarkers in subjects with KOA. Twenty-two participants with KOA were recruited and randomly assigned to IW (n=12) and CW (n=10) groups. The intervention took place 3 times/week over a 6-week period. The participants in the IW group completed two 15-minute bouts of walking exercise with 30-40 minutes of rest between the two exercise bouts. The participants in the CW group completed 30 minutes of walking exercise without rest. Pain was assessed using the visual analogue scale (VAS) and the Measure of Intermittent and Constant OA Pain (ICOAP) scale at baseline and at the end of the intervention. The VAS was used to assess pain level after each session of walking exercise. The other measurements at baseline and end-intervention included the 6-minute walk test, systolic blood pressure (SBP), resting heart rate (rHR), heart rate recovery (HRR) and maximum heart rate (MHR), serum level of inflammatory cytokines including interleukin (IL)-6, IL-8, IL-1β and IL-10, and C-reactive protein (CRP). There was a 25% dropout rate from the IW group and a 10% dropout rate from the CW group. The compliance to IW (96.29%) exercise was significantly higher (p<0.05) than to CW (78.39%) exercise. There was a significant decrease of VAS scores in both groups; however, there was a significantly higher (p<0.001) decrease in VAS scores in the IW group than that in CW group. In addition, ICOAP score was significantly reduced in the IW group (p<0.05) but not in the CW group after the intervention. After each exercise session, there was a significant decrease in VAS scores in the IW group (p<0.05) but not the CW group. There was a significant improvement in the fitness level for the IW group but not for the CW group after the intervention. The participants in both the IW and CW groups did not show significant changes in SBP, rHR, HRR or serum level of CRP, IL-6, IL-8, IL-1β and IL-10. The results of this dissertation project indicate that IW exercise may reduce pain and improve compliance to walking exercise better than CW exercise while being comparable with CW exercise for improving fitness levels in people with KOA.

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