This leaves large room for error and traditionally this area of a bike fit has been particularly poorly managed.
When we think of balance on a bike, for most riders the concept of left/right balance comes immediately to mind. While symmetry of function is, of course, very important on a bike, the concept of fore/aft balance tends to take a back seat (pardon the pun). This article will attempt to cover some of the basics of the concept of forward balance and describe the issues that may arise if your seat setback is far off where it should be.
The Primary Drivers
While cycling, the knee extensor (quadricep group) and the hip extensor (gluteal group) musculature both tend to be the primary drivers of downwards pressure on the pedals during the power phase of the stroke. As the leg finishes its downwards “stomp” on the pedal, there is a transition from knee extension to knee flexion which is controlled by the hamstring group, and a small “pull” effect which comes in across the bottom of the stroke due to this.
In an ideal positional scenario, the relative activation of these muscle groups, which originate from the pelvis and attach onto the leg in various locations, is in balance, and the rider will display reasonable pelvic stability, while not throwing too much weight forward or backwards onto, or off, the bars. Newton’s third law tell us that for every action, there is an equal and opposite reaction, so particularly if the hamstring group is being underutilised due to a positional issue, the tendency will be for the rider to “tip” forward.
This occurs as the quadricep group preferentially pulls the rider’s pelvis anteriorly due to its origin at the front of the pelvic arches while the hamstring is on holidays relaxing. The net effect is an increase in load towards the front of the bike, and onto the hands of the rider.
Consider a hypothetical rider whose seat is placed 20mm further forward than ideal. The hamstring group is poorly utilised across the bottom of the stroke as there is such a small window of crank angle to contribute to the leg flexion control that it is underutilised to a large extent.
The rider’s hamstrings switch off, their quads drag them forward onto the bar and they develop hand numbness, neck tightness and shoulder pain – the possibilities are endless.
Move the rider’s seat back to the appropriate setback and the hamstring control switches back on for a reasonable arc of crank rotation, the pelvis stabilises and the hamstring starts to control the stroke effectively. The rider’s weight comes off their hands and the above problems disappear.
It is worth noting at this junction that similar effects occur if the seat is too high or hugely too low, or if the cleat position is too far forward for that rider’s individual technique.
Even something as far removed as insufficient arch support to stabilise the feet, or a gross issue with Q-factor, can contribute to relatively poor hamstring control across the bottom of the stroke, and can be a factor in upper body issues on the bike – as with everything biomechanically related to the bike, it’s not as simple as we would like it to be.
Most riders look for the causation of a local symptom at its site. For example, hand numbness is very often treated by varying bar style, bar width, bar height and so on. More often than not,
I find the causation of hand, wrist, shoulder and many neck problems is actually located in the fore/aft position of the saddle, combined with the seat height, cleat position and so on disturbing the proper balance of the rider, causing them to grip the bars heavily to stabilise themselves, throw weight forward onto their hands excessively and so on.
The common issues that typically occur from improper fore and aft balance vary almost as much as each individual varies when it comes to pedalling technique. The most common by a long way is hand numbness arising from sustained gripping of the bars, and compression of the median nerve pathway through the small canal in the wrist.
The medical term we’re all familiar with is carpal tunnel, but there are plenty of other variations with subtle differences between them. All are caused by the same issue – too much demand for heavy grip and too much weight forward on the bars.
Other common issues the rider will complain of are tightness and pain in their trapezius muscle group (upper shoulder), mid-thoracic pain and fatigue, tricep soreness, base of neck pain and lower limb issues – frontal knee pain being the primary one in the lower half of the body.
It can also be a clue if the rider complains of trying many different saddles but always feeling excessive perineum pressure – among other possibilities this can be a clue that their seat setback may be too far forward.
So the question becomes, how do we set seat setback when fitting a rider? An experienced bike fitting professional with a good eye will be able to look at your posture on the bike and make a pretty accurate determination on seat setback, within a 3mm tolerance, once all of the other potentially contributing factors are removed from the system.
If you are playing along at home and trying to sort yourself out, try pedalling on a trainer at a sustainable threshold load and, with your hands initially on the hoods, swing them back next to your hips and continue riding at the same effort level. If you are able to stabilise yourself there, without feeling as if you’re going to faceplant onto the bar, with only a mild increase in cadence or a slight tendency to tip forward, you are likely pretty close to being on the money with your setback and general position.
This means that when you place your hands back on the bar, you have just enough weight on them to steer the bike, but not so much that you’ll develop problems. Steve Hogg taught me this trick many years ago as a good gauge of balance on the bike and all credit for this technique must go his way.
It’s worth noting that any attempt to set seat setback based upon angle measurements of the knee/hip/torso complex will so often be hugely removed from reality as to render them entirely useless for our purposes.
If you’ve had an angle-based fit before, don’t be afraid to experiment and deviate away from the recommended seat setback (and height) if you are still having issues with feeling too heavy on the hands.
Neill is a sports physiotherapist with a special interest in cycling biomechanics, injury prevention and management, and complex positional cases. He has been fitting riders for around 10 years and has himself raced at a club and state level (with no particular distinction!) for many years. He now resides on Queensland’s Sunshine Coast and works from Cam’s Cycling Collective in Brisbane.