Seat Height - How low can you go? No, thats too low....
Like most aspects of a good bike setup, seat height adjustment is a balancing act of compromising power and muscle optimisation, with risk of injury and overuse conditions. Excluding a heroic crash, most cycling injuries result from overuse of particular muscles/tendons, and getting your seat height correct is a great way to minimise repetitive strain through your lower back, hips, knees, and ankles.
Long story short:
Seat too low = Increased knee compression and shear forces
Seat too high = Lateral pelvic rotation and ankle loading
Seat just right = More power!
Historically there are a few methods people use to get a rough estimate of a good seat height; the LeMond method, the Hamely method, the Heel-Toe method, and Video Geometry method. The effectiveness and scientific support for these methods are discussed in my latest blog article, which will allow you to make better decisions regarding an optimal setup for your style of riding.
For a detailed biomechanical analysis of both body and bike, book a biomechanical bike setup assessment with John, visit 6s.com.au or contact our Mingara or Ettalong clinics.
Seat height:
There are a couple of easy ways to hurt yourself while riding a bike.
Crash
Ride too much and develop an overuse injury
For most cyclists, excluding any heroic stacks or interactions with friendly motorists, the main reasons for pain while riding is from repetitive strain to tendons or joints. Most people have the pre-conceived belief that a lower seat and slacker geometry is better for ‘comfort’ riding, and the opposite is true for racing. This is wrong.
Usually there is only a small range of suitable adjustability before both power and comfort are compromised. I have had a couple of clients in the past who were quite elderly and rode only short distances, so their ‘expert’ bike shop had set them up with a very low seat and upright riding positions. One of these clients couldn’t even ride up hills without significant knee pain and thigh muscle fatigue, but the bike shop dismissed her concerns and suggested her “knees are probably worn out, maybe you need joint replacements”…
Needless to say after making some very simple adjustments to her seat height, alongside other small tweaks, this client can now ride up hills without any pain or undue fatigue, and she now cycles almost every day for the sheer joy of riding. Moral of the story, if you have pain talk to a physio, and don’t take medical advice from a mechanic.
There has been a lot of published research in physiology and sporting journals on the best bike setup for improving outcomes for competitive and recreational cyclists. When delving into seat height optimisation, there is a pleasant consensus of what is suitable for most cyclists, and the difference in setup for professional vs. beginner cyclists is fairly small.
For starters, let’s discuss why seat height is such an important thing to get right.
Seat too low = Increased knee compression and shear forces
Seat too high = Lateral pelvic rotation and ankle loading
Seat just right = More power!
This is the simplest way of putting it. Cycling relies mainly on generating power from hip extensors (gluteus maximus >hamstring), and knee extensors (quadriceps), and balancing movements using synergists (hip flexors, calf muscles). The biomechanics are complex, but optimising the co-ordination of all these muscles requires all the joint angles to be creating a “mechanical advantage” at each stage of the pedal stroke.
A mechanical advantage describes the length-tension relationship of muscles, when compared to joint angle. In layman’s terms, how to get the most power out of a muscle with certain energy input. Therefore getting all your joint angles right, in just the right positions, with make you a faster and more efficient rider. Adjusting the seat height is a great way to optimise the hip, knee, and ankle joints, which are of course the most important bits for cycling.
Now that we can understand the need for getting the seat right, what is a good way to do it?
There have been a number of methods used to calculate the best seat height, from the very scientific and skeletally optimised, to simply “winging it” if it feels right.
Depending on the age of who you ask, most experienced cyclists will quote the Greg LeMond Method, which involves measuring the distance from the floor-to-crotch of the cyclist in barefoot standing, multiplying it by 0.883, and this is supposedly the ideal distance between the saddle and the bottom bracket of the bike. Not perfect for everybody, but not a bad starting point.
The Hamely Method is another way of calculating an ideal seat height. Similar to the LeMond method it uses the floor-to-crotch measurement, this time inferring that 1.09x that distance should be the distance from the seat to the pedal, when the crank is down and parallel to the seat tube. Again, not a bad starting point, but we can get more scientific for better results.
Oddly enough using the Heel-Toe method produces very similar seat heights to the above methods, and some published research finds this is actually better at getting close to the ideal knee flexion at bottom-dead-centre.
The ideal knee flexion at bottom-dead-centre is the primary goal for good seat height adjustment. Based on multiple studies, the suggested range lies between 25-35deg, when measuring the angle subtended by the greater trochanter of the hip, the lateral femoral condyle at the knee, and the lateral malleolus at the knee. The difference in power output and efficiency at this range is minimal, but changes greatly outside this range.
Studies have shown closer to 25deg may be slightly more efficient, but increases stresses at the ankle, and though the iliotibial band (ITB). Closer to 35deg seems to be the best compromise to minimise all joint stresses, with a debatable, almost immeasurable decrease in power efficiency.
The Lemond, Hamely, and heel-toe methods generally yield knee flexion in this range, which is why they can be very useful. But clearly, high-speed video analysis combined with joint angle calculation will yield an exact number, thus allowing the perfect seat height to be discovered. In most physiology studies this is now the “gold standard” being used to ensure good control of the knee angle for each cyclist.
Based on the biomechanics of a cyclists body, in terms of pure efficiency, the seat height should be quite similar for road cycling, and for mountain biking. Of course, being perched quite high up on a mountain bike can decrease the bike control on rough descents. Over the last few years ‘dropper posts’ have allowed the best of both worlds, with the ability to drop the seat down a couple of inches instantly with the flick of a switch, and then return back to normal with another flick. For any serious mountain biker, they are a must.
So have a go at setting your bike seat in a more ‘optimal’ position, and feel the difference it makes to your riding comfort and performance.
For a 16-point biomechanical bike fit, including seat height evaluation and advice, visit 6s.com.au and book an assessment.
