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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Elsevier
2025-08-01
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| Series: | Experimental Gerontology |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S0531556525001329 |
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| author | Emily J. Parsowith Emma Herring Brandon Cohen Kevan S. Knowles Ethan C. Hill Meredith Chaput Abigail W. Anderson Matt S. Stock |
| author_facet | Emily J. Parsowith Emma Herring Brandon Cohen Kevan S. Knowles Ethan C. Hill Meredith Chaput Abigail W. Anderson Matt S. Stock |
| author_sort | Emily J. Parsowith |
| collection | DOAJ |
| description | 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. |
| format | Article |
| id | doaj-art-6cd657888ab74d65b6bd2fbbf5a1fa4d |
| institution | OA Journals |
| issn | 1873-6815 |
| language | English |
| publishDate | 2025-08-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Experimental Gerontology |
| spelling | doaj-art-6cd657888ab74d65b6bd2fbbf5a1fa4d2025-08-20T02:09:04ZengElsevierExperimental Gerontology1873-68152025-08-0120711280310.1016/j.exger.2025.112803The influence of chronic knee pain and age on conditioned pain modulation and motor unit controlEmily J. Parsowith0Emma Herring1Brandon Cohen2Kevan S. Knowles3Ethan C. Hill4Meredith Chaput5Abigail W. Anderson6Matt S. Stock7Institute of Exercise Physiology and Rehabilitation Science, School of Kinesiology and Rehabilitation Sciences, University of Central Florida, 12494 University Blvd, Orlando, FL 32816, United States of AmericaInstitute of Exercise Physiology and Rehabilitation Science, School of Kinesiology and Rehabilitation Sciences, University of Central Florida, 12494 University Blvd, Orlando, FL 32816, United States of AmericaUniversity of Central Florida College of Medicine, Medical Education Building, Health Sciences Campus at Lake Nona, 6850 Lake Nona Blvd, Orlando, FL 32827, United States of AmericaInstitute of Exercise Physiology and Rehabilitation Science, School of Kinesiology and Rehabilitation Sciences, University of Central Florida, 12494 University Blvd, Orlando, FL 32816, United States of AmericaInstitute of Exercise Physiology and Rehabilitation Science, School of Kinesiology and Rehabilitation Sciences, University of Central Florida, 12494 University Blvd, Orlando, FL 32816, United States of AmericaInstitute of Exercise Physiology and Rehabilitation Science, School of Kinesiology and Rehabilitation Sciences, University of Central Florida, 12494 University Blvd, Orlando, FL 32816, United States of AmericaInstitute of Exercise Physiology and Rehabilitation Science, School of Kinesiology and Rehabilitation Sciences, University of Central Florida, 12494 University Blvd, Orlando, FL 32816, United States of AmericaInstitute of Exercise Physiology and Rehabilitation Science, School of Kinesiology and Rehabilitation Sciences, University of Central Florida, 12494 University Blvd, Orlando, FL 32816, United States of America; Corresponding author.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.http://www.sciencedirect.com/science/article/pii/S0531556525001329AgingMotor unit controlChronic painPain efficiencyFunctional muscle quality |
| spellingShingle | Emily J. Parsowith Emma Herring Brandon Cohen Kevan S. Knowles Ethan C. Hill Meredith Chaput Abigail W. Anderson Matt S. Stock The influence of chronic knee pain and age on conditioned pain modulation and motor unit control Experimental Gerontology Aging Motor unit control Chronic pain Pain efficiency Functional muscle quality |
| title | The influence of chronic knee pain and age on conditioned pain modulation and motor unit control |
| title_full | The influence of chronic knee pain and age on conditioned pain modulation and motor unit control |
| title_fullStr | The influence of chronic knee pain and age on conditioned pain modulation and motor unit control |
| title_full_unstemmed | The influence of chronic knee pain and age on conditioned pain modulation and motor unit control |
| title_short | The influence of chronic knee pain and age on conditioned pain modulation and motor unit control |
| title_sort | influence of chronic knee pain and age on conditioned pain modulation and motor unit control |
| topic | Aging Motor unit control Chronic pain Pain efficiency Functional muscle quality |
| url | http://www.sciencedirect.com/science/article/pii/S0531556525001329 |
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