LEG DOMINANCE: What to do about human asymmetries on a perfectly symmetrical machine.

In this blog I want to talk about leg dominance and how it can have a significant effect on cycling injuries.  Leg dominance refers to the fact that almost everyone pedals a little bit harder with their favoured or dominant leg.  This is much like hand dominance where most (if not all) of us have a preferred hand for writing and ball sports.  It indicates that for many of us we probably have cerebellar hemisphere dominance in the brain that favours one side over the other.  In fact it’s rare to see someone pedal absolutely symmetrically with 50% power coming from each side. 

So what?  Well in cycling, our bikes are perfectly symmetric (assuming that your levers are put on the bars symmetrically – which they often aren’t!), so if our body is asymmetric this can have some consequences.  What happens if an asymmetric body tries to pedal a symmetrical machine?

Often the result is pelvic instability.  In other words, on our dominant side, the pelvis tends to rotate forward and down (see video).  Similar hand dominance, this is more common on the right hand side.  Many cyclists seem to be unaware of this phenomenon when riding.



If our pelvis rotates forwards and down on one side, there are three obvious consequences although please note that not everyone adapts to this in exactly the same way; there are other possible ways for the human body to adapt than those mentioned below. 

The first consequence is that our lower back moves excessively and may get sore, often producing a typical pattern of muscle tightness or imbalance (where the quadratus lumborum (QL) muscle in the lower back and less commonly the psoas or hip flexor muscles become tight and painful on the dominant side). 

The second consequence is that this pelvic wobble or rotation on the saddle can cause saddle soreness, often more noticeable on one side of the perineum as the ischial and pubic rami rub onto one side of the saddle. 

The third consequence is that as the pelvis rotates towards the non-dominant side, the pelvic movement tends to cause the knees to rotate.  So for a right leg dominant person, the right side of the pelvis rotates forward (when viewed form above this looks like the entire pelvis rotates anti-clockwise or to the left).  This tends to drag the right knee closer towards the top tube, and the left knee out away from the top tube as shown in the image below.  Have a look at your own knees when pedalling and see if they are equally spaced from the top tube.  If they’re not, one possible cause can be leg dominance.  

Image: as the pelvis rotates forwards on the right, the right knee is twisted inwards and the left knee outwards.

WHY DOES THIS MATTER?  Because knees like to travel in straight lines, not be twisted inwards or outwards.  When this happens, often the result is knee pain.  Now which knee I hear you ask?  Well it varies and eventually both may become painful, but usually one side hurts first and this is most likely related to whether that individual can tolerate inwards or outwards movement better. 

Now if your pelvis is rotating asymmetrically, please don’t jump to the conclusion as you read this that it has to be leg dominance that is the cause.  There are many other possibilities such as a leg length difference, asymmetric leg muscle tightness and so on that need professional assessment before a clear diagnosis can be made. 

If almost everyone has at least some minor (or even major) tendency towards asymmetry, when do you normally start to see symptoms?  In my experience, if the asymmetry is relatively minor you may not experience any issues until you’ve been riding regularly for a season (ie a year) or more.  What seems to happen with training is that whilst both legs get stronger, the fact that you are pushing a little bit harder on one side with every pedal stroke leads to the dominant leg getting even more dominant / stronger than the non-dominant side over time.  Gradually the asymmetry becomes more and more pronounced, so after a season or two, depending on mileage, the barely detectable asymmetry is more easily detected and may be starting to cause some problems.  

So how do we “fix” the problem?  Since all movement is ultimately controlled by the nervous system, we have to consider how likely it is that we can completely balance or correct a hemisphere dominance.  The chances of creating perfect symmetry are highly unlikely.  It’s a little bit like asking a right hander to write left handed, although the effect of dominance in cycling is substantially easier to correct that this.  

What we can do is incorporate some drills into your cycling that help to restore the balance back to something approaching symmetry, much like it probably was before you started cycling regularly.  How do we do this?  There are several drills you can perform on your bike such as one legged pedalling and fast pedalling (at high cadences).  These drills, providing that you emphasise pelvic stability and form, can gradually help to not only restore symmetry and eliminate the unwanted pelvic compensation, but can also smooth out your pedalling technique and help teach you to pedal in perfect circles.  Other drills can also help like riding a fixed gear bike once or twice a week (especially on rollers where there is a real need to be more symmetric and develop good core stability).  Off the bike, one leg strength drills are a must (see our post here regarding one-legged strength drills).

When do these drills get incorporated into your program?  For racing cyclists, we usually recommend performing them regularly in the aerobic base or pre-season phase, and then during each recovery week of the season.  This helps to restore the symmetry that can gradually be lost of the race season and to prevent the injuries that tend to go with the pelvic rotations.