What is the difference between deformable and non-deformable structure and materials? This question requires careful consideration and is relevant during the saddle selection process. The answer can be found within structural engineering and physics, assisting our decision-making process when working alongside cyclists of numerous cycling styles and disciplines. The differences are relevant when considering various forces that the body is subject to whilst riding a bicycle. Load, stress and strain in the form of vibration and oscillations are transferred to the pelvis, spine and upper body through the saddle. The saddle is also the central point responsible for anchoring the body’s weight on the bicycle. There is interest not only in body position and biomechanics, but also saddle material, construction and design when facilitating return following injury.

For deformable structures / bodies, the underlying assumption is the structure will undergo deformation or change in shape when load is applied depending on the intensity of load. For non-deformable bodies, the assumption is there will never be any deformation or change in shape. A non-deformable structure is considered as ‘ideal rigid’ when deformation is zero or so small that it can be neglected. Another way of defining this is measuring the distance between two points on a rigid body whilst applying external force. The distance of these two points will remain constant on a non-deformable body regardless of external force. 

As a bike fit consultant and cycling specific physiotherapist, an informed decision on saddle selection can then be made with this knowledge. The characteristics and differences that exist between saddle base material are important and relevant considerations for comfort, safety and efficiency for both body and bicycle. It goes without saying that differences will exist between carbon fibre and non-carbon fibre saddle structures. Carbon fibre offers excellent rigidity and strength to weight ratio, high levels of fatigue and heat resistance. Carbon fibre is well suited to support high levels of stiffness and strain, introduced to bicycle construction methods in the early 1970’s.

Differences also exist between carbon fibre structures and quality, often understated within the cycling industry. There are differences in carbon fibre material, weave pattern and manufacturing process that can influence the deformable characteristics of the material. Carbon fibre can be graded according to quality and respond quite differently in certain applications based upon design structure. These features enable us to look beyond the top cover appearance of a saddle and seek further information related to the construction method and process, knowledge that can help achieve longstanding comfort, safety and efficiency goals related to bike positioning across many different cycling styles.

Adrian Spinelli
Physiotherapist + Bike Fit Consultant
Applecross Physiotherapy