The rough road to comfort………….

There is much talk of frame feel and comfort with debates focusing on frame materials and frame design. However, little seems to be reported regarding the science of comfort and feel. So lets have a look at what happens when we ride a bike along a road and just what it may be that is causing the feel and comfort we perceive……………

As we ride along a given road, collisions occur between the road and our bike, at the road / tyre interface of both wheels. The vibrations caused in cycling could be assumed to be a continuous oscillating input (Cardinale et al, 2005), and if we assume the bike to be a perfect transmitter of these forces then the oscillation occur in the bike and are passed directly to the rider. These oscillations continue in the riders soft tissue as a free vibration (vibrating at their natural frequency) where its amplitude will decay due to damping within the tissue. The reality is that the bike system too has a damping effect, which we will come to later.

When the body is exposed to such vibrations it employs a number of strategies to control the effects of such a stimulus. Nigg (1997) suggested that the body can in fact “tune” its muscle activity to reduce the detrimental effect the vibrations can cause. This provides advantageous as the work by Adamo et al (2002) suggest that prolonged exposure to vibration induces muscle fatigue in addition to Bongiovanni et al (1990) findings of reductions in motor unit firing rates and muscle contraction force. The mechanism that causes this is likely to be similar to that of exercise itself. Tiny tears in the muscle can occur, causing pain and reduced muscle function. Active muscles (like our legs turning the pedals) have been shown by Ettema et al (1994) to be more effective at damping externally applied vibrations. However, in order for the body to “tune” itself to reduce the effects of the vibrations, it has to use energy; energy which we may prefer to spend on peddling ! Ultimately however, the vibrations have the potential to cause discomfort and a reduction in performance.

For completeness however, it is worth mentioning the work of Bosco et al (2000) amongst other who have demonstrated that short term (10mins) exposure of specific frequencies (26Hz) and displacements (4mm) have led to an increase in athletic performance (measure by increase in strength and power). The effects of exposure to frequencies ranging from 15 – 60 Hz with displacements of between fractions of mm to 10mm, at accelerations of up to 15g are prevalent in academic literature. These studies have show both positive and negative influence on athletic performance. Interestingly there appears to be some links to the effects of such exposure and the subject fitness levels. So maybe there is a case that untrained cyclist are more likely to suffer discomfort due to a reduced capability at adsorbing the vibrations caused during riding. However, my own view on these studies remains positively on the fence until more robust experimental design has been applied (use of control groups etc). But interesting reading non the less, and demonstrates that it is possible that different frequencies, magnitudes and exposure times are likely to result in different physiological effects for different people.

Anyway back to the problem….

The natural frequency of a vibrating system will depend on its stiffness and its mass. In cycling terms, the vibrations the rider incurs will be dictated by the frequently of the impacts causing the oscillations (e.g. road surface, speed travelling). The oscillation frequency and magnitude may also be influenced by other parameters such as peddling cadence and peddling force profiles. Once the collisions have occurred, their transmission to the rider will be influenced by the mass of the system (rider + bike) and the systems damping characteristics. The damping characteristics being dictated by many things such as (in no particular order) tyre size and pressure, wheels (type, age, spoke tension, spoke quantity, material etc ), frame geometry, frame material, frame tube profiles, frame tube thickness, rider position, rider location (in the saddle, out of it), handle bar type and width, stem length and type, seat post type and height, saddle type and position, bar tape type thickness, clothing worn, fork design and material, bike age, quantity of drink in water bottle, etc…. The list could probably be a page long !

The resulting forces that are transmitted to the rider are likely to be what we perceive as feel. How these messages are “translated” by the bike to the rider and then how the riders body descrambles them could be critical in understanding comfort and bike feel.

So, to summarise, the type of oscillation caused during cycling may depend on the road surface, the speed travelling, the pedalling cadence, pedal force profile and mass of the system amongst other things. The transmission of these forces to the rider will depend upon the riders physiology, their mass and position on their bike in addition to the bike itself.

So what are we left with ? well it is possible that each rider and bike system will have a set of unique vibrations (frequency, magnitude, accelerations etc) and different abilities to deal with them. So, a bike system that is comfortable for me, or one that feels “right”, may not work so well for you. Equally, if I change the way I ride it (speed, position, cadence, pedalling technique) it is likely that the vibrations I receive will change and hence my perception of how the bike feels will also shift.

Therefore it would appear prudent to develop a bike system that is “customised” to some extent to your physiology, peddling style, fitness and intended end use. To some extent this happens naturally (through your position, tyre choices, saddle selection etc). However, there are a number of frame design influences that could also be applied to help this problem.

In the next Sunday School, we will have a chat about such parameters and see that its never as straight forward as we would like!