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Items filtered by date: August 2014
Monday, 11 August 2014 00:00

Aero shrug

There are a number of adjustments that can be made to your bike that have an effect on power production, comfort and aerodynamics. A successful bike fit will gather information on the relative importance of each of these three aspects and then adjust accordingly. For example a track pursuit rider will be interested in optimal aerodynamics and power production at the expense of comfort (pursuiting is very uncomfortable regardless!) whereas for a long distance cyclist comfort takes on a much more important role. For every athlete and every event there will be a slightly different balance that must be achieved. What is often not addressed in bike fit sessions is the different ways a cyclist can sit on the same bike to get a very different position to the one intended. Tony Martin offers an extreme example of this in the picture below but there are more subtle tactics that can be employed to safely increase your performance.

Tony_Martin_aero_descent

An example of this that many of the PBscience athletes have been using over the past seasons is the 'aero shrug'. It's another item that I was reminded of at the recent WCCS in a presentation by Andy Froncioni (twitter: @AndyFroncioni) of Alphamantis technologies. Oli is much more of an expert on aerodynamics than me and describes the shrug as follows:

"Press your chin forwards and down towards the top of your stem, then 'shrug' your shoulders towards your ears (it should feel like they roll up and in over the back of your neck). Keep your head still and relaxed and maintain the natural curve of your spine."

They say a picture saves a thousand words so the following two shots in a layby on the Farnham 10 course are the perfect example of the aero shrug from Jill. Using the shadow behind as a frame of reference you can see how much the head position is dropped and the light patch on the grass shows how much narrower her shoulders become.

Jill_non-shrugJill_shrug

Onto Andy's presentation at the WCCS... if you're not convinced by measurements using shadows and light patches of grass (!), then the following slide shows calculations of CdA for mulitple laps on a velodrome. Alphamantis technologies have developed a robust means of evaluating aerodynamics with field testing. If any of you have used Golden Cheetah's aerolab feature you'll understand the gist of this. The following slide gives the results of this technology applied to our aero shrug. The first five laps establish a baseline, before we see the effects of a shrug on 6 laps and then a final four laps back at baseline. Now we have data showing that a shrug can have a real and measurable difference on a rider's aerodynamics.

Aero_shrug_data

A few caveats:

  • the effect of a shrug will vary for different riders, some will benefit greatly and others not at all
  • sustainability is a problem - you can overcome this a little with practise but it can be quite uncomfortable. In Andy's slide you can see the effect wearing off in the last two laps, presumably as the athlete struggles to hold the position. So a pursuit rider might be able to hold said position for the whole of their race with practise but in a road TT may need to pick certain sections, for example headwind sections.
  • because of problems with sustainability, it might also be possible to make changes to your position that have a similar effect to the shrug (head drop, narrow shoulders). This would be preferable to having to force yourself into position!
  • Similarly, improved flexibility/mobility through the arms, shoulders and upper back are of importance when adpoting an optimal head/shoulder position.

Give it a try in front of the camera and see if you can spot a difference. It might be worth a few seconds in your next race against the clock! 

Published in Blog