Weird question. Lately my diaphragm feels constricted for the first 20 minutes of my runs and rides. I wouldn’t call it a pain so much as a ‘presence of pain’ if that makes sense. Makes it hard to take a deep breath, like I am only getting 80% of my lung capacity. Curious if anyone has experienced this.
thanks, brian
Just curious: does this ever happen outside of training, and are you under any noticeable stress?
I think you are supposed to take them out before exercise.
I LOL’d at that one.l
I think you are supposed to take them out before exercise
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do you have allergies by chance?
Undiagnosed asthma perhaps? Or fighting/recovering from Bronchitis?
My first thoughts as well 
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I have this problem, but it only happens at the start of the run during a tri. It’s not related to hydration or nutrition. It is definitely related to exertion, as it only occurs when I’m going hard in a short-course race. I thought it was exercise-induced asthma, but I’m not so sure. My new theory is that my abdominal muscles get kind of constricted during the bike, since I’m hunched over. So, my new approach is to go through a couple of very quick oblique stretches, either while on the bike coming into T2 or in transition. Seems to have helped.
stress? probably more than some people, but nothing that has picked up recently. my spitballing hypotheses were: (1) training in the early morning (not warmed up, not stretched and cold) and (2) chronic fatigue/overtaxed. do these hold any weight?
and yes, as i typed this i knew i was setting myself up for some smarmy replies 
I’ve been told that exercise-induced asthma presents when you STOP. So shortness at the beginning of the run doesn’t sound like exercise induced asthma. This was according to my docs
what kind of stretches? is it all related to weather?
The stretch involves any kind of side lean that creates a stretch on the oblique abdominals. So, like a triangle yoga pose would work, but not on the bike! You know the “old-man” stretch people were forced to do in gym decades ago, where you put your hands on your hips and lean your upper body left and right? That works, too. On the bike, I try to emulate that motion in some way.
I don’t think weather has anything to do with it, though.
So it feels like you cannot expand/fill your diaphram?
do you sleep face down?
Try taking off your heart rate monitor.
Increase your caffeine intake lately? I know I have that probably if I drink too much caffeine.