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If you’ve ever ridden a particularly rough section of tarmac or taken a road bike onto terrain it wasn’t designed for, you’ll know how unpleasant the resulting vibrations can be. As it turns out, ‘whole-body vibrations’ can be a little more serious than just uncomfortable – over time they can increase the risk of various ailments, including low back pain, spinal degeneration, and more.
The dangers of whole-body vibrations are often discussed in the context of those driving vehicles or operating heavy machinery for a living, but given cycling also has the potential to regularly expose riders to vibration, it’s a topic worthy of discussion for those of us who like to ride.
Timothy Holsgrove is a senior lecturer of Biomechanics & Bioengineering at the University of Exeter in England. As he writes in the following article, there’s been little research about the impact of whole-body vibrations for road riders. He and his colleagues set out to change that.
Back pain is common among the general population, but studies have shown that more than half of professional cyclists have suffered from back pain in the previous 12 months. Meanwhile, recreational cyclists riding more than 160 km per week are 3.6 times more likely to suffer from back pain compared to those that ride less than 160 km a week.
However, whole-body vibration is just one of many causes of back pain, so it is valuable to know what the level of vibration is during normal road riding and whether this is a potential cause for the increases in back pain associated with riding greater distances. And most importantly: what can be done about it?
My colleagues and I wanted to measure the whole-body vibration during normal road riding in a group of 10 regular recreational and competitive cyclists. This would allow us to compare the vibration levels during cycling with the limits used to protect workers from high levels of vibration in jobs such as bus, train, and heavy-goods-vehicle drivers. We also wanted to see what effect different equipment would have on the vibration exposure, so we decided to compare three different seatposts, as that is a convenient upgrade that a cyclist might make to improve the quality of their ride.
Each participant in our study used their own bicycle, which all had 27.2 mm seatposts. This allowed us to switch their seatpost with the three we were testing and compare the difference over a 6.4 km road route that combined both rough and smooth tarmac. The three seatposts we tested were the Fizik Cyrano R3 (aluminium alloy), Canyon S13 (carbon fibre), and the Canyon S15 (carbon fibre). All were a similar mass (215-220 g), but varied in retail price from £92.99 for the Fi:zi’k Cyrano R3, through £136.95 for the Canyon S13, to a total of £244.89 for the Canyon S15 including the Ergon flip head kit necessary to fit the oval rails of the Prologo saddle.
The two Canyon seatposts are designed to be vertically compliant and laterally stiff, and the S15 seatpost has a dual leaf-spring design to achieve this. Therefore, we expected to see lower vibration exposures with those two seatposts compared to the Fi:zi;k R3. We used the same Prologo Scratch 2 PAS NACK saddle for all tests so that the saddle didn’t affect the transfer of vibration between the seatpost and the rider. All tyres were adjusted to 95 psi at the start of the tests. (More on tyres in a moment).
We used sensors to measure the vertical, fore-aft, and sideways accelerations at the seat cluster, saddle rails, and at the lumbar region of the spine. These accelerations were then processed to work out the vibration exposure, called the “vibration dose value”.
We found that the level of vibration was high in all seatposts. Even over the short 6.4 km route, the daily exposure limit (as defined by a European Union Directive) of the vibration dose value was exceeded with all seatposts by an average of over 70% at the saddle rails, and over 13% at the lumbar region of the spine (see chart above). The seatposts did not make a significant difference to the vibration exposure; for some riders the S13 or S15 seatposts reduced the exposure compared to the R3 seatpost, but for others it was similar, or increased the exposure.
Our results also showed that the exposure to vibration was due more to multiple shock loads due to bumps and changes in the road surface, rather than general low-magnitude and high-frequency road buzz.
Cycling is an activity that leads to improved fitness and health, but our results show that it does also lead to substantial exposure to whole-body vibration, which increases the risk of back pain. Therefore, there is a benefit in choosing equipment that can reduce vibration. That said, it is often difficult to know what will work, or what products provide the best value for money.
We found there was no difference in the vibration exposures between the three seatposts. The linkage mechanism combined with an elastomeric insert that the Cane Creek Thudbuster ST uses might work better than the seatposts we tested to reduce vibration, but this comes with a significant weight penalty (580 g) compared to most road seatposts. Therefore, we think that other equipment such as the frame, tyres, or saddle might offer better potential to reduce vibration without large increases in mass.
We found the vibration at the lumbar region was much lower than at the saddle rails. This is expected and is due to a combination of the saddle, soft tissue of the participants, and their clothing such as the chamois of their cycling shorts. However, it may be challenging to improve the design of the saddle to further reduce vibration without increasing weight or reducing the support that it provides, and preliminary data we have measured on a small number of participants confirms this. Therefore, we believe that the frame and tyres are a good place to focus on to reduce vibration.
There are a wide range of ways to reduce vibration both at the front and rear of the frame. Indeed there are already lots of examples on the market other than the use of frame compliance due to geometry, thickness and material, including short-travel suspension (Specialised Future Shock, Lauf Grit fork, Pinarello EDSS), and pivoted frames (Trek IsoSpeed, Cannondale Kingpin). However, these systems generally result in a heavier frame, and there isn’t any data about how successfully they work to reduce vibrations compared to a standard road frame.
The increased popularity of wider tyres combined with lower pressures may provide a dual advantage of reduced rolling resistance and reduced vibration. However, initial measurements we have taken on 25 mm tyres suggest that there is little difference in the vibration exposure between 75 and 95 psi. More tests on larger-volume tyres would be valuable to understand if they can reduce the shock loads present during cycling as well as the low-magnitude road buzz, and ultimately provide a low-cost way to reduce the vibration exposure during road cycling. We are currently doing some work on tyres but COVID is making it difficult to complete research on human participants even in non-invasive studies like this.
So where does all of this leave us? Well, if you are riding on roads that are rough enough that it feels uncomfortable, then they are probably also rough enough to lead to a fairly high vibration exposure. You can try to reduce the vibration you are exposed to by seeking out good quality, smooth roads. And lowering your tyre pressure might also help, though not so low that you risk a pinch flat or damaging the rim on any bumps.