Knee trouble? Cycling loads it far less than running

"My knee hurts. Do I have to give up sport?" It is one of those questions people ask quietly, often after someone in a consulting room has uttered the word osteoarthritis. A German study has just put figures on something many veteran cyclists suspected: minute for minute, cycling loads the knee considerably less than running and, if there is osteoarthritis, less than walking too.

What they measured

The study, published in the Scandinavian Journal of Medicine & Science in Sports, was carried out in the biomechanics laboratory of the German Sport University Cologne with 56 recreational or competitive cyclists, none of them sedentary: they rode around 6,000 km a year. Nineteen had diagnosed knee osteoarthritis (aged 40 to 65, most at an advanced grade on X-rays), another nineteen were of a similar age and healthy, and eighteen were young and also healthy.

Each participant pedalled at nine combinations of cadence and power (from 60 to 100 revolutions per minute and from about 160 to 260 watts), walked briskly (about 5 km/h) and ran at an easy pace of just over 5:30 minutes per kilometre. Using motion capture cameras plus pedals and force plates that measure loads, the researchers calculated the cumulative load on the knee during one hour of each activity. Rather than looking at the peak of each stride or pedal stroke, they used a model that gives more weight to big impacts, because cartilage, like any material, fatigues more under large loads than under many small ones.

What they found

In plain terms: the bike lets you do a lot of aerobic work, the genuinely tiring kind, with little punishment for the joint. That fits with what clinical guidelines already recommend, as they advise aerobic exercise for people with knee osteoarthritis, and it helps explain why so many patients feel better in the saddle.

The caveats, because there are some

Before you sell your running shoes, here are a few buts that the authors themselves point out. The participants were active cyclists with few symptoms, so the results may not apply to someone in a lot of pain, who cannot run or who is starting from scratch. Also, 210 watts is not a gentle ride to the shops: it is a serious pace for a trained club cyclist. Everything was measured in a laboratory, at constant cadence and power, which is nothing like a real ride with hills and traffic lights.

Most importantly, the index they calculate is mechanical, not clinical. They did not measure pain, cartilage on MRI, or how osteoarthritis develops over time. What the study shows is that cycling loads the knee less; whether that translates into less pain or slower progression of osteoarthritis remains to be proven. The study was funded internally by the university and the authors declare no conflicts of interest.

How to apply it on your rides

For more on that last point, read why flat-out hill efforts do not replace weights, and if you are torn between the road and the turbo trainer, here are the reasons why riding outdoors usually wins. And if you fancy putting a scoreboard on your rides, cycling kilometres also count in the Victoris Hermes Challenge.

Finally, the usual reminder, because it matters: the bike is no substitute for a doctor. If your knee swells, locks, gives way when you put weight on it, or hurts at night or more and more, it is time for an appointment before any more kilometres. With a clear diagnosis and a bit of common sense, there are many years of pedalling ahead. And for once, your knee will thank you out loud.