Running may increase the risk of knee osteoarthritis (OA) onset or progression for some people, but in many others the knees will be safe during running; in such individuals, the benefits of physical activity can positively affect weight management and other means of reducing OA risk.
By Nicole M. Cattano, PhD, LAT, ATC; and Jeffrey B. Driban, PhD, ATC, CSCS
Osteoarthritis (OA) is a complex joint disorder defined by structural changes, pain, and other symptoms. People often describe OA as “wear and tear” of the joint. OA often affects weightbearing joints such as the knee and hip. Researchers and clinicians commonly debate whether running is good or bad for joint health.1,2 Some say the repetitive “pounding” of running increases the risk of lower extremity OA,1 while others note the benefits of running (eg, maintaining a healthy body weight, improved function) that may reduce the risk of OA2.
As with many things, the answer is not just black and white. After all, if you excessively drive your favorite car for years, it will eventually break down and you will need to replace it. Conversely, if you leave your car parked on the street for a year and never use it, then you will have problems with it, as well. This analogy can also be applied to the joints of the body, and finding the right balance is critical to long-term joint health. If you overdo it, you ruin it—but if you don’t use it, you lose it.
Using it vs overdoing it
There is a delicate balance between joint tissue remodeling and loading, and maintaining this balance is critical to joint health. Research suggests deviation from this homeostasis is associated with OA onset and progression (Figure 1).
Although physical activity is a major component of joint health, this relationship can also be confounded by other things, such as a history of joint injury. Animals that have been casted or immobilized demonstrate cartilage changes and OA onset;3,4 suggesting that if you don’t use it, you lose it. Physical inactivity and obesity are also associated with more severe pain in patients with knee OA.5
Conversely, research also suggests that if you overdo it, you ruin it. Animals that perform highly repetitive activities had more joint inflammation than those who were less active, along with early cartilage changes indicative of OA onset and progression.6-8 These highly repetitive activities also caused a decrease in animal strength and performance over time, likely due to increased symptoms and subsequent pain avoidance.8 Although pain avoidance may seem to be a good thing, it can actually cause more harm. Changes in motion can shift loads to other areas of the body that are not used to sustaining such loads and ultimately increase OA risk at other joints, in addition to the involved joint.
Similar results have been observed in humans. For example, elite skiers, who train and compete more often than less competitive peers, are at higher risk for hip or knee OA.9 Furthermore, elite long-distance runners are more likely than nonathletes to develop knee OA.10 This indicates excessive overloading may be an important risk factor for lower extremity OA. Although elite-level sport participation may be associated with a higher risk, it remains less clear whether it is the peak loading forces or the repetitive forces experienced over time that contribute to this increased OA risk.
Peak loading vs cumulative loading
Excessive peak force through a joint may cause pain and ultimately increase the risk of injury and long-term complications. However, the relationship between peak loading and symptoms can change based on knee OA severity.11 In patients who had moderate knee OA, greater peak load was associated with increased knee symptoms. However, researchers found the opposite in patients with advanced knee OA, in whom greater peak loads were associated with fewer knee symptoms. The findings of this study may be related to pain avoidance patterns or changes in joint integrity and structure.
The quality of joint motion over time, and how the forces are dispersed across a joint throughout every step of the day, may be better related to the “wear and tear” associated with OA. Therefore, cumulative loading, or loading over time, may be more important than peak loading when considering OA development. Researchers found no differences in peak adduction load between patients with and without knee OA. However, they reported cumulative knee adductor load was more accurate in distinguishing adults with and without knee OA than measuring peak adduction moment alone.12 Cumulative knee adductor load (the sum of the amount of knee adduction experienced throughout all steps in the course of a day) was twice as high in patients with knee OA compared with patients without knee OA.12 This supports the hypothesis that patients with knee OA move differently than patients without knee OA, and could be associated with changes in symptoms or pain-avoidance patterns. Several things may influence cumulative loading and joint health, such as the intensity of loading, the frequency of loading, the duration of activity, as well as rest for recovery. Sudden or drastic changes in any of these components could influence how a joint tolerates loading.
A person’s regular physical activity level may reflect the amount of load a joint typically experiences and may determine a threshold for how much load a joint can tolerate. For example, a group of highly active individuals had no biochemical marker changes associated with cartilage breakdown after a light 30-minute run.13 In a separate study in which participants were analyzed based on reported physical activity level, more active individuals had smaller increases in cartilage degradation markers after a 30-minute run than less active individuals.14 This evident dose-dependent response suggests the running task was not difficult enough to cause joint stress and metabolic changes in this highly active cohort. Clinically, it also suggests individuals can gradually train their bodies to sustain running loads in a healthy manner.
The dose of the physical activity experienced by an individual may influence joint metabolism and, ultimately, long-term joint health. Walking and running cause temporary biochemical changes reflecting cartilage turnover that return to baseline levels within a couple of hours.15-18 These changes are elevated more drastically and take longer to return to baseline with longer-lasting activities, such as a marathon or ultramarathon.19,20 Body weight and altered biomechanics can also adversely affect joint loading. Walking with a greater body mass was associated with greater increases in cartilage degradation, which took longer to return to baseline than in individuals with lower body mass.21
Running and cartilage load
Training interventions appear to mitigate the changes in joint metabolism observed after a running task. After a 12-week running program the increases in biochemical makers of cartilage turnover that were previously seen after a 30-minute walking activity were drastically reduced; similar reductions were not seen in individuals who had completed 12 weeks of swimming or cycling.16 This suggests the running program allowed joints to adapt over time to be able to withstand a running load. Clinically, it is important to understand that gradual increases or changes in training are needed to allow the tissues time to adapt to load in a healthy manner.
If a person runs consistently throughout their life while avoiding joint injury or sudden changes in running inten-sity, duration, or fre-quency, then the benefits of running likely outweigh the risks of developing OA. In a large cohort of adults, those who reported a history of running were no more at risk for OA than those who had no history of running.22 Habitual running may in fact reduce the risk of OA by helping individuals maintain a healthy weight and body mass index. People who reported a history of running were likely to have a lower body mass index than nonrunners, and we believe this relationship may be protective against OA development and progression.22
Although most people tolerate running well, this may not always be the case. Highly active people who reported lower quality of life had greater increases in inflammation after a 30-minute run than those whose quality of life was better.12 People who have advanced-stage OA (bone on bone) may need to be cautious with their weightbearing physical activities to avoid worsening symptoms.23 Also, as noted above, elite long-distance runners may also be at risk for knee OA. However, for these elite athletes, it remains unclear if their risk for OA is because of the high mileage or frequency of their training, their history of injuries, and/or their management of those injuries (eg, running with pain or returning to sport too early). Most of the evidence relating a history of sport participation to lower extremity OA is of low quality and is almost exclusively based on data from men, despite women representing a large portion of the US athletic population.10,24 In two recent systematic reviews, researchers reported injury may be a major influence that explains why some elite athletes are at higher risk for OA, especially in soccer.10,24
Finding a balance
The Physical Activity Guidelines Advisory Committee provided overwhelming evidence in its 2008 report to support a physically active lifestyle.25 These findings included the conclusion that a physically active lifestyle does not increase OA risk. However, the expert panel’s findings regarding OA risk do not necessarily apply to elite-level or extreme athletic activity. Finding an appropriate balance in activity may be critical to joint health. Clinicians should encourage patients to be physically active, and when there is concern about a person’s risk for OA onset or progression, they should promote forms of physical activity, such as swimming or moderate running, that are less likely to increase that risk. After all, exercise is a common component of OA treatment guidelines and a key to long-term wellness.26
Clinicians can use what is known about physical activity and OA to help educate patients about long-term joint health. However, self-reported physical activity levels may not be accurate enough to rely on independently. Patients with OA overestimated their self-reported moderate to vigorous physical activity minutes by an average of seven minutes compared with objective data from an activity accelerometer.27 Clinicians and patients should carefully monitor symptoms in addition to physical activity levels; patient-reported outcomes may help identify people who are putting their joints at risk. Although running may increase the risk of OA onset or progression for some people, many people will be safe running and will gain the well-documented benefits of physical activity, which can be a positive strategy for weight management and other means of reducing OA risk.
Finding the appropriate balance of physical activity is critical to long-term health. Educating our patients about risks and healthy lifestyles will help them in their long-term battle to prevent OA onset and progression. Paying attention to joint symptoms, current physical activity levels, and making gradual changes to training programs will assist in efforts to live a healthy and pain-free life.
Nicole M. Cattano, PhD, LAT, ATC, is an assistant professor and athletic trainer in the Department of Sports Medicine at West Chester University of Pennsylvania, who works clinically with the university basketball teams. Jeffrey B. Driban, PhD, ATC, CSCS, is an assistant professor in the Division of Rheumatology at Tufts Medical Center and Tufts University in Boston.