Purpose: To evaluate the effect of a 20 minute walking stimulus (20MWS) that is intended to simulate participation in daily activity on self-reported pain, ambulatory function (walking speed, vertical ground reaction force (GRF), and stance time) and knee joint kinetics in older adults with chronic knee pain. Acute exercise is known to exacerbate pain in osteoarthritis (OA) on a short term basis, however very little is known about patient compensations to acute flares of OA pain. Understanding the motor system adaptations to pain may provide insight into short and long term efficacy of pain therapies and their impact on joint health. We hypothesized that there would be significant increases in pain and concomitant decreases in ambulatory function and joint kinetics in response to the 20MWS in adults with OA related knee pain. Methods: Seven older adults (62.3 +/- 6.2 years; 24.8 +/-2.8 kg/m2) were enrolled in the study after completing the informed consent process and a Physical Activity Readiness Questionnaire (PAR-Q+). Inclusion criteria were ages 50-75 years, BMI <35 kg/m2, good general health, met the American College of Rheumatology clinical classification criteria for OA in at least 1 knee, ability to walk unaided, no history of cardiovascular or neurological disorders. Knee symptoms were evaluated using the Knee Osteoarthritis Outcome Score (Table 1). For the 20MWS, subjects walked on a treadmill at a pace similar to their preferred overground speed. Pain was evaluated on an 11 point verbal numeric pain rating scale in the first and final 2 minutes. Gait analysis was performed pre and post 20MWs while subjects walked overground on an 11m walkway at preferred and faster than preferred speeds. 3 trials per speed were collected at each timepoint. External inter-segmental moments were calculated for the lower limb using an inverse dynamics procedure. The primary gait outcomes were: walking speed, maximum vertical GRF, time in stance on more affected leg, peak external knee flexion, adduction, and internal and external rotation moments on the more affected leg. A 2 x 2 factor Analysis of Variance (ANOVA) with time (pre, post) and speed (preferred, faster than preferred) as main effects was used to test for significance with alpha = 0.05. If significant interaction effects were found post hoc paired student's T-tests were used to test the null hypothesis that the change in primary outcome is not different from zero for each speed. Effect size for the difference was calculated using the Cohen's d statistic. Results: In response to the 20MWS there was a small but significant change in knee pain (mean change 0.43 +/- 0.56; p=0.05). Significant speed by time interaction effects were found for walking speed, time in stance on more affected leg, and 1st max vertical GRF. Post-hoc testing found that at the faster than preferred walking speed there was a significant decrease in walking speed, an increase in stance time and a decrease in the 1st max GRF in response to the 20MWS (Table 2). No significant differences were found at the preferred walking speed in response to the 20MWS. Moderate effect sizes (d>0.5) were also found for the change in 1st and 2nd peak knee adduction moments at the faster than preferred speed and the max knee external rotation moment at both the preferred and faster than preferred speeds (Table 2). Conclusions: In agreement with the hypothesis, in response to a 20MWS there was an increase in perceived pain along with a decrease in ambulatory function and a trend for changes in joint kinetics. The changes in ambulatory function were found only at the faster than preferred speed. These changes would be expected to decrease the force magnitude and loading rate acting across the knee and are consistent with a pain withdrawal response. The reduction in the external rotation moment at the knee would contribute to reduced torsional load and may protect from further increases in joint pain. However, there was a trend for an increase in the 1st and 2nd peak knee adduction moments suggesting a greater proportion of the joint load is acting across the painful medial compartment. This is unexpected based on classic pain withdrawal responses but may occur as a consequence of mild fatigue and/or pain- related inhibition of the knee extensor muscles. Further understanding of the motor system adaptations to exercise-induced disease activity is needed to optimize symptom management and exercise prescription in OA patients. (Table Presented).
Boyer, K. A., Jewell, C., & Hafer, J. (2015). Gait adaptations to exercise-induced flares of osteoarthritis related knee pain. Osteoarthritis and Cartilage, 23, A109–A110. https://doi.org/10.1016/j.joca.2015.02.827