Background/Purpose: Osteoarthritis (OA) is associated with limitations in physical activity (PA) for many reasons which are not fully understood. While pain can be associated with reduced PA, other biomechanical and psychological factors can also be limiting. Walking energetics, specifically the amount of energy used for walking relative to total energy capacity, has been proposed as a mechanism by which PA is reduced in older adults. Fatigue is a common symptom of OA and has been linked to reduced PA in this group. Fatigability is a separate but related construct that may also be associated with PA in people with OA. These factors have not been previously investigated together. The purpose of this study was to evaluate the association of walking energetics, fatigue, and fatigability on PA in people with knee OA. We hypothesized that people who use an increased amount of energy for walking, experience more fatigue, or are more fatigable are less active.

Methods: We tested our hypothesis in 29 people with knee OA (age 58 ± 9 years, 10 M/19 F, BMI 33.5 ± 5.8 kg/m²). We assessed PA by self-report using the UCLA activity score. We used a six-minute walk test to measure VO₂max, then used a portable oxygen exchange system to measure percent energy used during walking (100 * VO₂rate/VO₂max) and VO₂cost at preferred speeds. We used the KOOS pain subscale to characterize pain. We used the PROMIS Fatigue survey and a treadmill-based fatigability test to assess overall fatigue and performance-related fatigability. We used Spearman correlations and regression analysis to test our hypotheses.

Results: UCLA scores ranged from 2, indicating “mostly inactive”, to 10, indicating “regularly participate in impact sports” (mean 5 ± 2). Percent energy used during walking, VO₂cost, fatigue, and fatigability were all associated with lower PA (Table 1). These associations persisted when controlling for pain. Together, pain, percent energy used for walking or VO₂cost, fatigue and fatigability predicted 57.7 to 58.4% of the variance in UCLA scores (p < 0.001). Fatigability mediated the association between percent energy used for walking and PA (Figure 1). There was no evidence that fatigue or fatigability mediated the association between VO₂cost and PA.

Conclusion: Walking energetic factors are important predictors of PA in knee OA even after controlling for pain. The effect of walking energetics on PA may work through its impact on fatigability. Walking energetics may be a useful target to promote PA in people with OA and may have beneficial effects on fatigue as well. The effect of biomechanical interventions for knee OA on walking energetics should be considered to avoid potential adverse effects on PA.

Fatigability mediates the association between percent energy used for walking and physical activity.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/walking-energetics-fatigue-and-physical-activity-in-people-with-knee-osteoarthritis/