I see your 15 minute VO2max interval, and raise you a 20 minute VO2max interval. 
Anyone that has gone out too hard during a 10 mile TT then tried to hang on for dear life knows this feeling! (Pretty much everyone!?)
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@GoLongThenGoHome that is VERY interesting! Iâve only ever experienced that at intensities below ~lactate thresholdâŚabove that intensity the âlong componentâ of VO2 holds primacy for me. HR always goes upâŚthe only question is how fast. Ha!
Iâm not sure why you see the HR response that you do but itâs fascinating.
Search for âVO2max verification.â Youâll find this paper as well as dozens more stretching back to the 1990s.
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I have read that the body is always trying to optimise things. Whatâs the least amount of energy it needs to use to complete a task?
Now it maybe when when my brain receives the signal from the muscles âWe need more oxygen etcâ it employs a series of strategies. So first of all it tells the heart to beat faster. But then I start breathing more efficiently and bringing more oxygen in per breath. It means my heart doesnât need to beat as fast to deliver more oxygen.
Does the brain ultimately know how much oxygen the lungs can exchange per breath given the rate and force of the diaphragm etc? We clearly have multiple inputs signalling the brain. I ultimately see a sub conscious calculation going on somewhere , where it is measuring the feedback loops on muscle oxygen use, oxygen / blood exchange in lungs, and HR and stroke volume. Then it decides what to increase or decrease.
A bit like the ventilatory thresholds. You know where your breathing changes? Initially just increasing HR was enough and then you really need to ramp the breathing up. Well as those thereâs also those times where you start breathing harder initially when you up the intensity but then the breathing settles down. Maybe as the breathing settles it gets more efficient, and therefore Har can decrease and the muscle still gets some amount oxygen.
Other thoughts. 