The influence of chronic knee pain and age on conditioned pain modulation and motor unit control
Background: Over 25% of U.S. older adults experience chronic knee pain, which worsens with inactivity, creating a cycle of pain, disability, and sedentary behavior. However, a limited understanding of the underlying mechanisms hinders the development of effective treatments. Purpose: This study inte...
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| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2025-08-01
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| Series: | Experimental Gerontology |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S0531556525001329 |
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| Summary: | Background: Over 25% of U.S. older adults experience chronic knee pain, which worsens with inactivity, creating a cycle of pain, disability, and sedentary behavior. However, a limited understanding of the underlying mechanisms hinders the development of effective treatments. Purpose: This study integrated assessments of Conditioned Pain Modulation (CPM) and motor unit control to elucidate the role of pain sensitization and neuromuscular impairments specific to chronic knee pain. Methods: Seventy-five participants were divided into three groups: young adults (n = 25), older adults without pain (n = 30), and older adults with chronic pain (n = 20). CPM efficiency was evaluated using heat and pressure test stimuli alongside a cold-water bath conditioning stimulus. Motor unit assessments involved isometric contractions of the dominant/painful quadriceps at 50 % of maximal torque, with surface electromyographic signals recorded from the vastus lateralis. Results: Independent of chronic knee pain, older adults demonstrated more efficient heat-CPM than young adults (p = 0.014, ηp2 = 0.080). The slope of the mean firing rate versus recruitment threshold relationship indicated that older adults showed greater firing rates for high threshold motor units, independent chronic knee pain (p = 0.010, ηp2 = 0.136). The y-intercept of this relationship was greater in younger versus chronic-pain older adults (p = 0.024, ηp2 = 0.111). Conclusion: Contrary to our hypothesis, older adults displayed more efficient heat-CPM, independent of chronic pain. Similarly, motor unit control was mostly influenced by age but not chronic knee pain. These findings suggest that age-related changes in pain modulation and motor unit behavior may play a greater role in neuromuscular function than the presence of chronic pain itself. |
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| ISSN: | 1873-6815 |