It's a long ongoing debate regarding aero position on a bike and the gains losses of being in a low aero position vs a higher one. People talk about how low or high your front end is in terms of aero dynamics, comfort, power output, and physiologic stress. I would like to address the respiratory system and how it is greatly influenced by the aero bar elevation in aero position. By no means am I saying I am the first to address this topic, but no where have I seen objective data presented that shows the respiratory systems abilities in a high position vs low. I am lucky enough to both have access to a Guru Dynamic Fit (DFU) Machine as well as a very portable respiratory monitoring device.
Here are the parameters of my experiment:
I set up two positions on the DFU, one in a position at the end of the riders functional range of motion for how low he can ride safely and one 90mm higher. Here is what I measured:
So, as you can see, the first 3 mins shows the riders ability to breathe in the low position and the last 3 mins shows their ability in the higher position. While in the low position there were some respiratory difficulties measured that could lead to a drop in performance. While the rider was quite able to breath over 5L breaths, he was struggling to maintain them consistently. Once I shifted the DFU into a higher position for the final 3 mins, his volumes and breath rate completely stabilized and relaxed. It's very interesting to have some objective data to support this theory of bike position.
This experiment was done at Kelowna Cycle on the DFU machine in our fit lab.