Can exercise therapy have an influence on endogenous analgesia in knee osteoarthritis patients? A systematic review and meta-analysis

Aim: To summarize the literature regarding effects of exercises on endogenous analgesia in knee osteoarthritis patients (KOAP).
Methods: The systematic review protocol was registered at PROSPERO (CRD42021237371). PubMed, Web Of Science, and Embase were systematically searched for studies investigating the acute and/or basal effects of exercises on endogenous analgesia in KOAP. If possible, a meta-analysis was performed. Risk of bias was scored using the Cochrane ROB 2.0 or ROBINS-I and strength of evidence was assessed by the GRADE approach.
Results: Nineteen studies were included; four studies investigated pain thresholds after an acute bout of exercise, while fifteen articles focused on basal levels of endogenous analgesia (as measured by pain thresholds (n=15), - facilitation (n=3), and - inhibition (n=2)). A meta-analysis combining two studies investigating acute effects presented that KOAP did not become more tolerant for pressure pain than healthy controls immediately after resistance training (p>0.05). Besides, one study with moderate quality of evidence showed that exercising KOAP had higher pain thresholds then non-exercising KOAP immediately after exercise (p<0.04). A meta-analysis combining three studies focusing on basal levels of endogenous analgesia showed that strength training of 6-12 weeks caused a significant increase in pain thresholds in KOAP, when compared to non-exercising KOAP (p<0.05).
Conclusion: Literature about this topic is scarce. Very low quality of evidence proved that strength training of at least 6 weeks is effective in increasing pain thresholds in KOAP. Moderate quality of evidence demonstrated that an acute bout of exercise effectively increases pain thresholds in KOAP