For those who don't know pectus excavatum or concave chest is when your chest looks like this
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This one is a mild case of it, its pretty common so a lot of people have it to some degree when its really bad it can look like this
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Anyway the point im making is this deformity can have direct offects on your breathing capacity ( usually only when its really bad ) because it compresses the lungs, it just came to my attention that some notorious fighters with not the best cardio have this deformity, like mcregor ( no pun intendeed) although his case is really mild
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But the worst case in the ufc is of edmen, who basically only got 1 round in the tank, he is a young guy so it can be just nerves and so on, but still... Thats something i think might have an effect on it
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Anyway this is just a theory and everybody is different, so thats probably not the case but hey, it might be it