>This is a key point.

>Aerobically "easy" won't line up with metabolically "easy" for very fit athletes.

>Typical pro triathlete:

>Power: 275W

>Lactate: 1.0 mmol/L

>Kcal/hr: ~1000

>VE: 100 L/min(!)

>While aerobically "easy", definitely not "through the nose" *or* metabolically easy

>Why quiet breathing through the nose for the bulk of your training is the key to knowing that you're at the right training intensity:

> The Aerobic Threshold or first rise in the lactate curve is a key training intensity.

>

> Primarily because it usually coincides with the highest rates of #FatBurning coupled with relatively low CHO oxidation, so the athlete can accrue a lot of work with minimal metabolic fatigue

>

> My buddy

> @feelthebyrn1

> always said that he could feel the AeT as:

>

> "the first deepening of the breath"

>

> In my experience, most athletes don't do a very good job of identifying this point & mistake their AeT for a point further up the curve. So, what should you be feeling?

>

> As the chart above shows, when an athlete begins a progressive metabolic test their VO2 (oxygen) requirements increase almost immediately & in fairly direct proportion to the exercise intensity. It makes sense then that we'd have to increase our breathing to match this, right?

>

> Wrong!

>

> Our body is pretty wasteful with O2 at rest. Our muscles don't take up most of the O2 in the blood & it just cycles around. Therefore, the first port of call when our body needs more O2 is simply for the muscles to take up more already circulating O2 from the blood...

>

> This shows up as an increase in the a-VO2 difference, i.e. the *arterio* *venous* *oxygen* *difference* - the difference between the amount of O2 in the blood of our arteries going into the muscle & our veins coming out...

>

> Because we already have this O2 'on board' our breathing doesn't need to significantly increase in depth or rate, at least initially, & we see both the VE (the amount of total air breathed per min) & respiratory rate to remain relatively steady.

>

> At a certain point (the AeT), the muscles ability to pull ⬆️O2 from the circulating blood can no longer keep up with demand & so it sends the brain a message:

>

> "We need more air, cap'n!!"

>

> And so, the first significant rise in VE (the amount of air moved through the lungs) occurs

>

> Fortunately, our body is equally lazy at rest when it comes to the lungs as it does to the blood and we have a lot of lung (tidal) volume in reserve.

>

> Therefore, at least initially, there's no need to increase breathing *rate*, our body cues us to just take *deeper* breaths.

>

> The "deepening of the breath" or "opening of the lungs" is generally felt as a need to move more air into the lungs than is comfortable through the nose & so the athlete, intuitively, opens the mouth to help out.

>

> And, this point, where we first kind of want to open our mouth to get enough air into the lungs is thus a good proxy for the Aerobic Threshold

>

> Importantly, it's quiet, it's subtle & not forced. IOW, it's not a competition to see how much air you can move through your nostrils😊