Low Prevalence of Hip and Knee Arthritis in Active Marathon Runners.
A frequent comment from patients is that they avoid running as they are fearful that this will cause “wear & tear” of the knees or hips. A consequence of this ‘loading equals degeneration’ mindset is that there is a general perception that running will give rise to early arthritis. This would appear to be logical when one considers the “pounding’ of the joints induced from long distance running such as occurs during a marathon. The evidence on this topic; however, does not necessarily back up this theory.
Several studies have show that distance runners do not have a higher incidence of hip & knee arthritis than non-runners. A recent study by Ponzio et al. (2018) found that marathon runners had a lower incidence of hip and knee arthritis when compared with the general population. Arthritis prevalence was 8.8% for the marathon running group. This was significantly lower than the prevalence in the matched U.S. population, which was 17.9%. The avaerage age of the study participants was 48 years of age and the group ran an average of 36 miles weekly. The non-marathon running group were matched by age, sex, body mass index (BMI), and physical activity level. The authors concluded that there was no significant risk associated with running duration, intensity, mileage, or the number of marathons completed.
It may be that the straight line nature of long-distance running is less likely to cause injury to the hip or knee when compared with other forms of exercise such as rugby, soccer and gaelic which tends to involve a lot of pivoting and change of direction. There is a also a greater risk of a trauma which can cause injury to the cruciate ligaments or knee cartilage. Individuals who suffer from a cruciate or cartilage injury to the knee have been shown to suffer from much higher rates of arthritis as they age.
Destruction and loss of articular cartilage is a central feature in most forms of arthritis. Recent research has suggested that the cyclic loading and unloading of cartilage induced from walking and running may actually be beneficial to joint cartilage. The cyclic movmenent has been shown to help maintain healthy cartilage in laboratory studies. Part of the reason for this is that the movement stimulates increase blood and nutrient supply to the tissues hence keeping them healthy. This may be one reason why striaight line activites may give rise to healthier knees in the long-run when compared to actiivties involving pivoting or potential trauma. This may be one reason why the runners in this study fared better than athletes in the comparison group who may have participated in riskier sports than were associated with an increased risk of knee injury.
Does Body Fat Impact on Arthritis Risk?
There are several factors that drive joint degeneration. General inflammation is one such cause. Fat cells have been demonstrated to increase the production of inflammatory markers in the body. Fat cells (adipocytes) contain self-defensive macrophages (immune cells) which have been shown to produce cytokines (pro-inflammatory proteins). Therefore, the greater the fat percentage, the greater the inflammation in the body. Runners, by having a lower body fat percentage, would generally have lower inflammatory markers in the body. It is also likely that frequent runners are more health conscious and therefore may consume a healthier diet and avoid other poor health choices such as smoking and drinking alcohol excessively.
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