Why does pain stop people with knee problems from staying active?
Full reference: Stephanie Louise Smith, Muhammad Umar Habib, Wendy J Chaplin, Bonnie Millar, Daniel F McWilliams, David Andrew Walsh, Central aspects of pain associated with physical activity: results from the Investigating Musculoskeletal Health and Wellbeing cohort, Pain Rep. 2025 Apr 18;10(3):e1268. doi:
10.1097/pr9.0000000000001268
Knee pain is a common problem, particularly among individuals with osteoarthritis. The central nervous system plays a role in both pain and physical activity. Being active can help manage pain and improve health. However, many people with knee pain find it hard to stay active, even when their pain improves, which can lead to obesity, increased risk of other conditions and worsening pain. This study investigated why this might be.
The researchers examined data from over 700 adults with knee pain who participated in a larger UK study. They focused on a specific questionnaire called the Central Aspects of Pain (CAP), which assesses how the central nervous system might amplify pain, sometimes known as nociplastic pain. Nociplastic pain is a type of chronic pain where the nervous system becomes sensitised, causing pain even without tissue damage or nerve injury. The CAP questionnaire includes measures of fatigue, sleep difficulties, low mood, anxiety, and widespread pain. These factors indicate that pain arises not only from joint damage but also from how the body and central nervous system process it.
The team discovered that individuals with higher CAP scores were more likely to be physically inactive, even after accounting for pain severity. Over the course of a year, those whose CAP scores increased were more inclined to cease being active, while changes in pain scores alone did not explain this shift. This indicates that the way the central nervous system processes pain may serve as a more significant barrier to physical activity than the pain's intensity itself.
Interestingly, no single factor, such as fatigue or depression, alone explained the results, although low mood seemed to play a significant part. This suggests that it may be the combination of factors like mood, sleep, and the extent of pain that prevents people from remaining active.
The study also found that simply reducing pain (as measured by traditional pain scales) did not automatically lead to people becoming more physically active. This helps explain why some individuals who have surgery or treatment to reduce pain still don’t return to being active.
The findings suggest that helping people stay active may require more than just treating the pain. Interventions that also target how the central nervous system processes pain, such as exercise combined with psychological support, may be necessary. Understanding and treating these central aspects of pain could help individuals with knee pain remain active, maintain their independence, and enjoy a better quality of life.