Sitting Pretty DIY Bike Fit Part 2
Determining your ideal saddle height and setback seems a simple concept at first but there’s a lot more to it than just finding a comfortable height where your knees don’t lock out. Steve Hogg explains the detail of saddle ergonomics in this second instalment of DIY Bike Fitting.
Before moving to the process of fitting yourself, a bit of background is necessary for what follows.
A Challenge is any factor that decreases rider stability or performance. Challenges can be Functional or Positional. Examples of Functional Challenges are things like differences in leg length, postural distortions, differing patterns of flexibility or stability between left and right sides etc. Examples of Positional Challenges are matters like too high or too low a seat height, poor cleat position, too great a reach down or out to the bars and many more.
The thing to note is that any challenge will cause the Central Nervous System (brain and spine) to automatically attempt to compensate for the challenge. This happens at a level below conscious thought so most riders are not aware of the compensatory response. Patterns of compensation don’t solve a problem; they only shift the load elsewhere.
The Central Nervous System is incredibly adept at compensating for suboptimal function or position but almost invariably, any pattern of compensation involves an increase in the difference between right and left side function. To recap what I said in the first instalment of this article, a bicycle is a symmetrical apparatus in a positional sense, so ideally, the rider needs to function as symmetrically as possible. In an effort to achieve that aim, we need to remove as many challenges and compensatory responses to the riders position as possible and then minimise the effects of what can’t be changed. This is a must because although the CNS compensates for less than ideal conditions incredibly well, it has no predictive foresight as to the long term consequences of any pattern of compensation. So a compensatory response that works in the short term may cause injury over a longer time frame, with the body part most loaded or least equipped to bear the compensatory load being the first one to protest.
Lastly, all compensatory responses have an individual flavour. This means that if you see 20 people with the same issue with their position, you will see 20 differing attempts to compensate for the issue. Many will be similar, but at least one or two will be mildly surprising and occasionally, there are individual responses that are just ‘out there’.
Most riders sit too high because they set their seat height while riding on the flat where the momentum of the bike’s forward movement allows the rider to coast through the ‘dead zone’ (either side of top and bottom dead centre in the pedal stroke where the rider has little leverage). In contrast, hill riding requires the rider to drop their heels more and consequently, extend their legs more than they do while riding on the flat. The most effective seat height is the one that allows a rider to ride a hill well while seated.
There are many ways used to determine ideal seat height, but only one method applies to you as an individual. Here’s how to go about it:
Find a hill that takes at least three minutes to climb. Warm up thoroughly and then ride up the hill under significant load in one gear higher than you would normally feel comfortable. I would define ‘significant load’ as similar heart rate or power output as you would use during a time trial effort.
Do you feel as though each leg is reaching through the bottom of the pedal stroke fluently and without a hint of jerkiness?
Do you feel as though both sides of the seat are evenly loaded?
If the answer to one or both questions is “No”, drop your seat 3 mm and repeat the effort / drop seat 3 mm cycle as many times as necessary until you feel as though both legs are reaching through the bottom of the pedal stroke fluently and that you are bearing your weight more or less evenly between left and right sides of the seat.
If the answer to both questions was “Yes”, then raise your seat by 3 mm and repeat as necessary until you have found the seat height where you are just becoming aware that one or both legs have lost fluency through the bottom of the pedal stroke or that there is an increasing disparity between sides as to how you bear your weight on the seat. Once you’ve reached that point, drop your seat height by 3 – 5 mm.
If you said “Yes” to bearing your weight evenly on the seat but “No” to both legs reaching equally fluently through both the bottom of the pedal stroke, then either your perceptions are awry or you have a functional or measurable difference in leg length and it is worth having that possibility checked out by your manual health professional of choice.
If you said “Yes” to both legs feeling equally fluent, but “No” to bearing your weight evenly between sides on the seat, then you are not sitting squarely on the seat. As a diagnostic test, repeat the climb but pull the opposite hip to the side that feels like it bears more weight on the seat forward by 2 – 3 mm. Many will perceive this as twisting that hip forward whereas in reality most will be squaring up their hips to varying degrees. If holding yourself on the seat like that improves the symmetry of left / right weight bearing and does not have any negative impact on left / right pedaling fluency, keep practicing keeping the appropriate hip a tiny bit forward until that becomes your new ‘normal’.
If pulling one hip that 2 – 3 mm further forward exacerbates any differences between left and right side pedaling fluency, then your awareness of your position in space is likely not as accurate as you thought, so try pulling the other hip a tiny bit forward and reassess.
With care and a bit of method, the process outlined above should allow you to achieve an efficient seat height. Why is seat height so important?
If you are advising another rider on their seat height, the major visual cue is the velocity of extension (straightening) of the knee. If you see even the tiniest acceleration at the back of the knee as the leg extends, the rider has lost control of the movement. This will usually be obvious on the left side before the right side, though there are enough exceptions to make it worthwhile checking both sides. Here’s why this happens……..
When we apply force to the pedals, the gluteals (buttocks) and hamstrings combine to extend the hip (push the crank arm down) while at the same time the large muscles at the front of the upper leg, the quadriceps, extend (straighten) the knee. In practice the rate at which the quadriceps can contract is constrained by the hamstrings. If a rider is too high, under load and at a level below conscious thought (which is where the vast majority of decisions about matters of motor control are made), the rider will switch off their hamstrings as a self protection measure. That acceleration at the back of the knee mentioned previously now occurs because the rate of the quadriceps contraction is no longer constrained by the hamstrings causing an acceleration in knee extension.
When a rider sits too high, in the majority of cases they will not sit evenly on the seat and equally overextend both legs. Much more often than not, the rider will unconsciously pick a side to protect, usually but not always the right, and a side to sacrifice, usually but not always the left. This protection takes the form of a perceptible drop or forward roll of the right hip which in turn causes the left leg to overextend and provides a constant challenge to the plane of movement of the left hip. There is a left sided version of the same unconscious protective measure but it is less common. This favouring of one side over the other is the reason that left knee pain on a bike is much more common than right knee pain.
This is a tricky parameter to set because much of the method that I will explain is dependent on having an ideal or close to ideal handle bar position. But bar position can only be set once seat height and seat setback are ideal so we have to start with the seat. First, some background.
The basis for the method below is that the CNS (Central Nervous System / brain and spine) will always prioritise the muscles that allow us to hold a position on a bike at the expense of the muscles that generate power to move the bike. This results from the simple evolutionary imperative that a creature needs to be able to hold a position before it can attempt to move. Imagine trying to walk down the street while collapsing at the waist, hips, knees or ankles. It would be impossible. To prevent this, holding a position is prioritised over the ability to move as explained above.
So it follows that we need to arrive at a seat setback that allows the riders’ CNS the best possible chance to prioritise the muscles that load the pedals rather than the higher priority muscles that allow us to hold a position. In turn that means that we need to minimise the enlistment of the muscles that allow us to hold our position on the bike. We need a position that is largely passive and self-supporting and that requires minimal effort to maintain.
The way to accomplish this is to have the seat set back the minimum distance behind the bottom bracket that allows the rider to cantilever their torso out towards the bars without unduly loading the arms and torso. You should need your arms, but only just need your arms. At low speeds there should be some weight on your hands but any hand pressure should not be uncomfortable. As road speed and intensity of effort increases the upper body should become progressively less weighted until at the limit, the rider should feel like their upper body is near weightless. My feeling is that the rider should be sitting a fraction in front of their centre of gravity.
This approach has other benefits. You will breathe more efficiently. There are 20 torso muscles used in breathing, 18 of which have postural implications. By that I mean that those muscles can be enlisted to bear weight, resist pedaling forces or to stabilise with but they have to carry tension to do so. To breathe deeply and fully requires these muscles to carry little or no tension, so it is advantageous if these muscles are not enlisted or are only lightly enlisted.
The one failing with this ‘centre of balance’ approach is that it doesn’t work with dysfunctional riders. We’ve all seen them. They are the ones that grip the brake hoods in a death grip when riding hard. To be fair, for some who fit this description, their major issue is a poor position on their bike, but for many, the reason is that they are inherently unstable. The number of first time fit clients that I see who can’t perform a deep squat or a simple lunge is astounding. If you fit into this category, follow the above advice and try and achieve the best compromise possible. Let comfort be your guide…………………………and work to improve the way that you function!