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Article - 19 September 2011

The Aero/Metabolic Ratio - The Key To Bike Speed.

Here is a brief article I did for Triathlon Plus Magazine on a very interesting subject and one that remains close to my heart as I studied it at University! :-

The New Way to Ride Faster

The new advice that shows why the most aerodynamic riding position isn't always the fastest.

On a bike, enemy number one is aerodynamic drag. It is always present and will at all times be working against your attempts to go quicker. Gravity, by comparison, only slows you down if you insist on going uphill. As such, bike manufacturers work hard to convince us that their latest offering is the answer to a faster bike leg. However, it is worth remembering that the bike itself accounts for less than 20% of the aerodynamic drag we encounter, the rest is down to the rider’s frontal area – the part that hits the wind. Thankfully, this means that we can still buy some ‘free speed’ – tri bars, aero helmets and tight clothing all contribute to better streamlining. This helps to optimise air displacement and minimises the low pressure area formed in our wake, resulting in reduced drag. Essentially, anything we can do to get out of the way of the wind like getting down low on the bars and tucking in the elbows, will improve our aerodynamic profile. The answer to getting faster would seem then to be straightforward: buy the aero kit, tuck into the tightest ball possible and watch your bike split tumble. If only it were that simple. The reality is that the most aerodynamic position is rarely the fastest in practice. To maximise your potential and really go fast there are a few more things you need to know:

A few years ago I conducted a series of cycling tests at Brunel University on a group of triathletes. One of the key findings was that the tighter the aero tuck, the less power the less power the triathletes were able to sustain. Numerous studies over the last ten years have demonstrated similar findings. What is probably going on is that the aero tuck position either increases the work of breathing, compromises blood flow to the lower limbs or results in less than optimal biomechanics or a combination of all three. What we do know for sure is that generating power on a bike is almost always easier in a more upright, less aerodynamically efficient, position. Yet the best time triallists are very powerful in very aero positions and as a result go very fast indeed. One man responsible for getting this compromise just right is the Director of the University of Colorado’s High Performance Laboratory, Dr. Inigo San Millan. Formerly, an exercise physiologist with Garmin-Transitions pro cycling team, San Millan developed the concept of the ‘aero/metabolic ratio’. Rather than just using wind tunnel data to generate a position which is as aero as possible the idea is to also take into account the metabolic consequences of that new position. By way of example, last year I accompanied a cyclist whom I coach to a wind tunnel session. After several hours of testing I got him into the most aerodynamic position he could ever hope for. The computer predicted that his 40km time trial performance would improve by several minutes. In reality it did improve but only by 30 seconds. His power output also fell by 10% - an intriguing result – less power, yet still faster. Clearly, fine tuning this compromise has real potential. At the pinnacle of the sport, comparing aero positions in wind tunnels while monitoring the cyclists’ metabolic responses such as blood lactate values and the power that can be produced at race pace is all very well, but how should we, the average triathlete, use this knowledge to inform our own time trial position?

Firstly, ensuring that you are as aero as possible by sticking to tried and tested rules such as using tri bars, an aero helmet and ensuring that you keep your elbows tucked in, will all go along way to minimising your frontal area. For a no-nonsense approach to getting aero take another look at issue 30 (July) of Triathlon Plus in which Chris Boardman detailed just how to get really aero with the minimum of fuss. Once you have your extreme aero position then the analysis can begin. Firstly, you need to be aware of how your position feels. Do you feel powerful and generally comfortable or are you constrained somewhere? Try to understand where the problem is. Then, if you use a heart rate monitor (or better still a power meter) what sort of difference do adjustments to your aero position make to your heart rate or power numbers at any given effort level and especially at your race pace. What you are looking for is a position that feels strong, engages your core musculature, allows you to breath deeply and yet is never too far from the pure aero position you dialled in at the off. If you pay attention to both your cycling setup and subsequent performance in this methodical way there is no reason why you cannot both aerodynamically and metabolically optimise your own position. It really is not that difficult to do. I cannot guarantee that you will be mixing it with Tour de France riders but your best bike split is but a small set of compromises away.

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Read the previous article: Cycling sessions to target different fitness components

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