Risk of Developing Running‐Related Osteoarthritis is Intensity‐Dependent: Comment on the Article by Lo et al

Lo et al published an article in Arthritis Care & Research (1), suggesting that leisure-time running does not appear to be detrimental to the knees. Numerous investigations have been conducted to understand whether or not running might lead to osteoarthritis (OA) in weight-bearing joints (2–10). Unfortunately, however, the existing evidence seems to be insufficient for researchers to draw unequivocal conclusions (11). Similar to this study, the preponderance of data indicates that moderate level, or recreational, running does not increase the risk of OA of the knees for healthy people and that this activity might even have a protective effect (2–6). Our recent review concluded that running intensity, along with many other factors, could mediate the relationship between running and OA risk (12). As described, this cohort was not recruited based on elite running status, but from the community. Contrary to recreational runners, a link between running and OA risk has been extensively reported in ex-elite longor middle-distance runners (7–9). Even to non-elite runners, a significantly higher incidence of OA also existed in male recreational runners who were involved in high levels of running (10). Lo et al mentioned that those who run less may respond differently to running than the elite athlete (1) through a variety of mechanisms. One direct mechanism is that high-level running may induce high running-induced loading, which can be harmful to the joint once the magnitude exceeds the physiologic tolerance level for an individual. A biomechanical window has been suggested to maintain optimal cartilage homeostasis (13). Excessive mechanical stress can directly damage the cartilage extracellular matrix and shift the balance in chondrocytes to favor catabolic activity over anabolism, leading to the degradation of both collagen fibrils and proteoglycans (14). Another mechanism is that a high level of running may be linked with a higher incidence of joint injury (15), likely due to a distinct running pattern from recreational running (16). It is well recognized that the increased incidence of knee OA in runners may be attributed to a higher incidence of knee injuries (9). Previous joint injury is viewed as a biologically plausible effect modifier of the running-OA relationship, due to its effect on several potential mediators of cartilage degeneration, including secondary muscular weakness, joint asymmetry, biomechanical malalignments, ligamentous instability, and neurologic deficits (17). Normal strength and pace of periarticular muscular contraction may occur at the correct time for protecting the joint when impacts are transmitted to the lower limb. In this regard, an additional mechanism is that the high pain threshold (18) or the muscular fatigue in elite runners may lead to the impairment of subtle synchronization between the felt impact and the muscle response, probably leading to a higher risk for OA (19). In conclusion, the high level of running for competition is probably one of the major OA risk factors by these or other mechanisms (19). We therefore suggest that the risk of developing running-related OA is intensity-dependent. However, the causal relationship between running intensity and the risk of OA is yet to be determined. A clear understanding of the implications of these risk factors should increase awareness in both competitive athletes and the general population of the risks associated with running-related OA.