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One of the best things about cycling is its appeal for all ages.

Unlike many sports, such as running, the motions involved in cycling are smooth and impact free, which makes it much easier on ageing joints. By sitting on a bike with your feet on the pedals, your patterns of muscle and joint movement are precisely controlled and symmetrical on each side of the body – a big bonus for those seeking to avoid injury.

This contrasts with sports like running or swimming where the movement of the limbs has to be coordinated by the brain and neuromuscular system and where asymmetries can lead to injury.

However, recently published research by French scientists suggests that a symmetrical riding position does not always equate to symmetrical biomechanics in older cyclists, which could result in an increased risk of overuse injuries and premature fatigue during longer or harder rides.

The science
In the study, 11 masters cyclists who performed regular training and long-distance rides were each analysed for their pedalling biomechanics during an incremental cycling test. In particular, the researchers wanted to see if the cyclists typically pushed harder on one leg than the other.

The cyclists, whose average age was 53 years, were very experienced (riding between 4,500 and 14,000km per year) and considered themselves to have good technique. Also, none of them had sustained injuries prior to the study or were aware of any reason why they might have asymmetric pedalling biomechanics.

The 18-minute test consisted of 10 minutes at 100 watts, three minutes at 150 watts, three minutes at 200 watts, and two minutes at 250 watts. The test was conducted on a road bike equipped with an SRM crank system to accurately measure applied force and power as the cranks rotated. The rear wheel of the bike was mounted in a Tacx ergometer and the bike was adjusted so that each rider could ride in his optimum position.

During the test, the researchers recorded the average force applied by the riders at each point of the crank revolution for both left and right sides.

In a nutshell
When the data was number crunched, an index of asymmetry was produced for each rider where a score of zero per cent asymmetry equates to perfect symmetrical biomechanics (the forces applied to the left and right cranks as they rotate are exactly the same). For a ‘well-balanced’ cyclist, you would expect an asymmetry score of under 10 per cent.

However, except for one subject, the asymmetry scores were all significantly higher, regardless of the power level. Across the group as a whole, the average asymmetry score measured 30 per cent at 100 watts while at 250 watts, it averaged 23 per cent. In one rider, the value of asymmetry was nearly 60 per cent.

So what?
The degree of asymmetry between the left and right legs of the cyclists surprised the researchers not only because it was apparent at all power outputs and affected all but one of the group, but also because of the size of the L/R discrepancy in some of the subjects.

Putting aside the increased risk of injury, a large imbalance in force production between left and right legs is a recipe for premature fatigue; having one leg working harder to compensate for the other is always going to be a less efficient way of producing sustainable power than if both legs work equally hard.

Given these results, it could be beneficial to check your pedalling biomechanics (some stationary bikes such as Wattbike offer this facility) and perhaps perform some side-specific strength training – or pedalling using applied crank force feedback if 
a significant imbalance 
is present.

This article was first published in the June 06 issue of Cycling Weekly. Read Cycling Weekly magazine on the day of release where ever you are in the world International digital edition, UK digital edition. And if you like us, rate us!