Stuff I Learned – Diaphragm Fatigue

The Lead-In:
The Fall semester is rapidly winding down, and my final task is completing a project for Cardiorespiratory Adaptations to Exercise and Environment. Unfortunately, skiing daydreams are interrupting my progress on this project. I love to ski, and the recent cold snap has me thinking about ski trips past and future. Of my various skiing daydreams, I’ve been fondly remembering various backcountry trips in Colorado’s 10th Mountain System.

The air at Uncle Bud’s Hut does not contain a lot of oxygen.
(11.380 feet above sea level)

One dozen years ago, my old friend Steve and I made a late-Winter trip to Uncle Bud’s Hut, which is located at the wheezable altitude of 11,380 feet above sea level.  For some reason I was renewed in my interest in the supposed benefits of Yogic diaphragmatic breathing, and spent most of the 1600+ foot altitude gain focused on diaphragmatic breathing. By the time we arrived at the hut, I was not only hungry and tired, but nearly doubled over in pain. My entire midsection hurt, and the intense pain briefly convinced me there was something wrong with my spleen. While my spleen was OK, my diaphragm wasn’t so happy.

Stuff I’ve Learned:
As it turns out, diaphragm fatigue is very real, and the diaphragm’s central role in respiration means its response to fatigue has an outsized influence on performance. As many of you know, the diaphragm is a muscle, not dissimilar to the hundreds of other muscles in the human body. Muscles get tired, and when they do, they send predictable signals to the brain. Mechanoreceptors in the muscles more or less signal how hard the muscle is working, and metaboreceptors by and large signal how tired the muscle is. When you climb up the side of a mountain, mechanoreceptors and metaboreceptors in your leg muscles send signals to your brain that say “hey, I’m working hard and/or getting tired down here!”

My diaphragm hurt during most of this ski trip.

The diaphragm sends similar signals to the brain, though it seems as though the diaphragm talks louder than the other muscles. The diaphragm is richly innervated with metaboreceptors, and when it gets fatigued, the diaphragm loudly and clearly alerts the brain to the increasing work of breathing.

I’d never really considered the work of the muscles associated with breathing, though respiratory muscles may consume more than 10% of your aerobic capacity when you’re climbing up the side of a mountain. That leaves less aerobic capacity for the hardworking legs, which would explain why my legs felt so tired on that trip to Uncle Bud’s Hut. To ensure that I was breathing sufficiently to keep my blood oxygenated, my body automatically diverted blood from my leg muscles and sent this blood to my diaphragm muscle.

What have I learned on the side of the mountain and in the classroom? Don’t spend too much time messing with your breathing! Unless you clearly have a pathological breathing habit and or patterning, your body already knows exactly how to breathe. There are many variables involved (I discussed this in a previous blog that introduces the concept of DFWI), and your clever body keeps track of all those variables automatically.

The human body is really amazing. Again and again I’m awed by its clever adaptations. Your body is an embodiment of this precious human life; I hope that you can all stay physically active, get plenty of rest, connect with community, eat whole foods, and spend some time in silence during this busy time of year!

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