Saddle Geometry - Slide to the front, Slide to the back!

Bike seats come in all shapes and sizes. Additionally, there is also adjustability in tilt angle and how far forwards and backwards the seat rails attach to the seat post. Getting the seat position just right will make riding more comfortable, but can also be a great way to reduce risk of knee tendon injury.

Furthermore, correct alignment of the saddle will influence tibial angle at mid-stroke, improving quadriceps and gluteal efficiency.

Seat width and shape can be a personal preference, but a poorly selected saddle, especially with less-than-ideal geometry can lead to significant problems. Proximal hamstring tendonitis, patella tendonitis, lower back pain, and discomfort in the nether-regions are all signs of a poorly fitted and adjusted saddle.

Instead of switching through multiple (and expensive) saddles with no success, have your saddle geometry assessed to get the most out of your bike.

For information on how to get the right saddle geometry for your size and style of riding, check out John’s (6S Health’s resident Biomechanical Physiotherapist) blog article evaluating the latest biomechanical science behind selecting the best geometry for you.

To book a biomechanical bike setup assessment with John, visit 6s.com.au or contact our Mingara or Ettalong clinics.

Saddle geometry:

There are 5 contact points on a bike, being your left and right feet on the pedals, left and right hands on the handlebars, and your backside on the seat. Scientific studies have shown that the more power you generate with riding, the less weight you have going through the seat (because your legs are exerting more pressure). The converse is true too, that riding for long periods of time at an easy-moderate pace puts a lot of sustained weight through your perineum. This is quite an important consideration for anyone doing more than 4+hrs per week of cycling (which would almost be considered a rest week for most cyclists).

The more research I did on this, the more concerned I became. As a keen cyclist, I fit many of the risk categories for developing injuries and dysfunction from a poor seat choice (developing proximal hamstring tendonitis should have been a warning sign!)

Let me be clear. Poor saddle choice and geometry can be more than just a pain in the butt.

Most of the published research involving bike seats examines the role of regions of pressure into the seat, and the effect on blood flow and nerve conductance onto the surrounding genital areas. And it’s not good news.

4% of male cyclists experience “moderate to severe” erectile dysfunction. The problems can be temporary, or even last months after a long ride. Studies have shown a decrease in blood flow to the penis of over 85% when using certain types of saddles, and with rides often stretching for many of hours, fibrosis and connective tissue damage results. On top of the potential for severe blood flow issues, compression of the pudendal nerve leads to numbness in over 30% of cyclists, and over time reduces the sensitivity of the region.

And it’s not just the men. Female cyclists can develop compressive ischaemia under the pubic arch, leading to similar losses of sensitivity, and numbness with riding.

Fortunately, the research also shows good ways of improving the blood flow and nerve conductance to these areas, so enjoying cycling does not necessarily mean giving up other enjoyable things.

Based on published evidence, not on ‘clever marketing’, the following recommendations can be made regarding saddle choice:

1. Not too long! Saddles with an extended nose have been shown to have the greatest consequence to blood flow and nerve conductance to important regions.

2. Not too narrow! Width of the bike seat seems to be an important factor in ensuring good weight distribution through sensitive areas. The general rule of thumb is the back of the seat should support under your ischial tuberosities (sit bones), not wedged in between them.

3. The amount of padding has little to no effect on blood flow distribution. A generously padded seat may not give any benefit to comfort, and a good seat design is a more important consideration.

4. Grooves cut through the middle of the seat do little to improve blood flow. Again, avoiding long or narrow saddles is a much better strategy than simply choosing seats with ‘anatomical grooves’.

Once you’ve chosen a suitable saddle, the job isn’t finished there! Important considerations are: The tilt of the seat, and its fore/aft position, and these are usually adjusted with the seat post clamps on the seat rails.

So starting with the tilt. Usually a good rule of thumb is having the seat quite neutral (horizontal) to start with. Everyone has a different shaped pelvis, and different structural lordosis in their lumbar spine, and these factors may necessitate a slight tilt forward or back based on comfort. The best research indicates that the tilt shouldn’t exceed more than ~3deg forward or back, if mainly riding on flat ground. However things get more complicated when hills get involved. Take this example: If riding up a hill with 15deg gradient, the bike and seat will also be at 15deg elevation to horizontal. The cyclist however won’t be naturally inclined at 15deg, as gravity still acts vertically, and the best mechanical force on the pedals is with the cyclist still sitting in a similar vertical alignment (same as when riding on flat ground). The result is the seat digs up into the front of the pelvis at a 15deg angle, which is a fast route to pain and severe blood flow restriction.

The solution, if riding a lot of steep hills in a session, is to tilt the seat forward to oppose the change in gradient. This increases comfort, and performance. It’s worth doing, unless you like being slow and impotent. The tilt is much less relevant on the downhill sections, so it is a good compromise on “hill training” days. Tilt it back to neutral when riding sessions back on flat ground.

The final component of saddle setup is the fore/aft position. The rails on the saddle should allow a couple of centimetres each way. The primary goal of sliding the saddle forward or backwards is to improve the mechanical advantage of the quadriceps at the most anterior part of the crank revolution, that is, to align the kneecap directly over the pedal axle when it is at the 3 o’clock position. If the kneecap is a little behind the pedal axle, the hamstrings loading increases, wasting energy. If the kneecap is in front of the pedal axle, you may as well book in to see a physio to fix your developing patella tendonitis. Not to mention an increase in lactic acid accumulation in your thighs!

Sliding the seat can also cramp up or stretch out the back and upper body, which is why ensuring you get a full biomechanical bike fit is important.

A lot of bikes have multiple riding positions (e.g. road bikes with drop handlebars, TT bikes with forearm bars for aerodynamics), and the key to getting to best efficiency is to establish what positions the cyclist is going to spend the most time in. I have set up a few very competitive (National level track, Road, and Triathlon) cyclists, and had great results with ensuring the saddle is optimised for their ‘race’ position, rather than simply for the relaxed positions on training rides.

The moral of the story is, every component and its geometry can significantly affect your cycling comfort and performance. Talk to a biomechanical physio experienced in bike fits, and they can assist in improving your riding efficiency, and reduce risk of seat-related ‘complications’.

For a 16 point biomechanical bike fit, including saddle geometry evaluation and advice, visit 6s.com.au and book an assessment.