IS LOWER ALWAYS FASTER?

In the second article in this two-part series, UK physiotherapist Bianca Broadbent and physiologist Barney Wainwright – who are both bike fitters – discuss the need to individualise aerodynamic interventions to make athletes faster. Read the first part in Issue 2.

It can be difficult to gain insight into the process of aerodynamic optimisation thanks to the large number of biomechanical and aerodynamic factors at play — and their complex interaction.

These complexities mean that, sometimes, the optimal position involves making positional changes that may seem counterintuitive and may be contrary to some athletes or practitioners' beliefs.

However, these results and outcomes also demonstrate the importance of using an individualised evidence-based approach, where assumptions are minimised.

TRUNK ANGLE AND POWER

The assumption that a lower torso position is a fast solution reflects current bike positioning culture. However, this is a very reductionist approach and fails to consider the individual rider and their unique body shape and functional abilities. As can be seen in figures 1 (right) and 2 (next page), raising the cockpit 40mm resulted in a considerably more aerodynamic position for Cyclist A (37W lower power requirement to achieve the air speed), which was more sustainable and was found to offer an increased ability to produce power.

It should be noted that while these are examples where a relative increase in the cockpit height reduced aerodynamic drag, this is not a solution that is applicable in all cases, and for some anthropometric qualities a lower cockpit position can be more advantageous due to the changes in air flow that occur. This was certainly evident with Cyclist B — see later in this article — where widening the arm pads created space for the shoulder girdle to retract and as such allow the torso to adopt a lower overall position. The key element here, is that there will always be an interactive effect when a position is changed, as widening the cockpit would not have facilitated a lower torso angle had the saddle height not been lowered first.

Fig. 1a front on view of baseline position for Cyclist A

Fig. 1b front on view of final position for Cyclist A

Fig. 2a Baseline run Cyclist A

Fig. 2b set up 7, Cyclist A. Note that the despite the higher cockpit, this position created less aerodynamic drag, and was more comfortable and powerful than the forced baseline.

PAD WIDTH

Position sustainability is incredibly important for longer distance events, but also to permit large volumes of training in-position for short events. There is little point in adopting the fastest position in the wind tunnel if the cyclist cannot maintain nor ride in the race environment in that position. Despite this, there is a trend to adopt a narrow pad position as in many cases this reduces the frontal area.

There are many criticisms to this approach, namely that when the rider is producing power their head may be more likely to “pop up”, as it may to also improve vision, but it does not consider the flow of air around the rider.

Underwood et al. (2013) suggested that there’s high variability in aerodynamic drag with pad width and this is a very individual adjustment. If the cyclist does not have the anatomy or function to permit such a forced position, then a narrow arm pad position will create more issues than it will resolve (ContiWyneken, 1999).

Fig.e 3a: Baseline, Cyclist B

Fig. 3b: final position, Cyclist B. Note the lower torso angle because of widening the arm pads. It is important to iterate that the cyclist is able to see ahead in this position although it looks like they are looking downwards.

Figure 3 shows the baseline position for Cyclist B. In this position there is a great deal of strain through the shoulder and cervical musculature, with little opportunity for the head to be tucked. Widening the pads provided good proprioceptive and mechanical stability to the lateral forearm and allowed the head position to drop substantially.

Raising the hands of the cyclist so the forearm is inclined is another method that is commonly utilised to optimise the aero position. This “closing of the gap” more commonly facilitates a more relaxed shoulder girdle, and as such can allow the rider to pull down into a lower position figure 4, below). The aerodynamic outcome of this intervention is highly variable, with very high hand positions often obscuring view of the road, and sometimes increasing cervical extension.

It was agreed with Cyclist B that these interventions created a far more comfortable and sustainable position than the baseline and created a direction on which to focus in his preparations for upcoming races.

This process has created specific knowledge from which further refinements resulting from experience of long training rides and races can be put in place.

Fig. 4a: Frontal view of baseline, Cyclist B, with narrower elbows

Fig. 4b: Frontal view of of final position, Cyclist B, with wider elbow position

EQUIPMENT

The purpose of the examples in this article has been to present information on positioning. However, we have also included some data to show the effects of equipment choices that occurred in these sessions.

While some general trends exist, there is considerable variability in the impact of equipment that is determined by the environmental conditions experienced (air speed, direction) and the role its particular shape has on the whole system. Equipment can rarely be assessed in isolation.

Helmets are a good example of this, where the size and shape of a helmet on its own cannot determine how it interacts with the rest of the body. With cyclist A, we mentioned in our previous article that the large size helmet was not aerodynamically effective. However, the smaller size of the same helmet model increased the aerodynamic resistance by 7 Watts, or approximately 1.3 seconds over in her event. With cyclist B, the top tube mounted nutrition bag/box, which can often increase aerodynamic resistance, in this case reduced it by the equivalent of 6 Watts, or approximately 66 seconds over an Ironman race distance.

CONCLUSION

As with any commercial service that aims to be as cost-effective as possible, there will be some limitations on time utilisation, and prioritisation of the key areas for optimisation is crucial.

The examples and case studies we’ve presented across our two articles are not an example of a robust research study, but simply serve to highlight the potential gains that can be achieved with individuals for whom aerodynamics and power are highly important determinants of race outcome. There are many approaches that each professional can take when looking to optimise an individual’s position, which will be shaped by their background, experience, resources, and team.

Some may prefer to establish a matrix of possibilities, i.e. what are the fastest aerodynamic positions and how can they be facilitated biomechanically. Others, as we do, prefer to establish a robust biomechanical position on which aerodynamic refinement might occur. This 'functional window' allows us to ensure good adaptability, and crucially, the ability to hold a sustainable position whilst producing power.

Key priorities are to tailor the session to the athlete’s goals and ensure you consider the biomechanical and physiological demands of a position — the position with the lowest aerodynamic drag is not always the fastest overall.

Equipment will have an interactive effect with the position, and it is better to optimise this last.

The outcome that can be achieved is determined by the resources, approach, and experience available. If there is a good evidence base and a sound process, then a near optimum solution will be determined.

Bianca @thecyclephysio

Barney @bgwainright

Don’t forget you can read the first article in this series in issue 2 of Bike Fitter International.