There's a natural arch in the back which is natural. This arch is not very exaggerated one. Two things about the pics you posted:
Firstly, look at all the lower abs in these athletes and see how transverse abdominal layer has straighten the waist line there, that's the reason I always recommend pulling the belly bottom towards your spine while doing abs to train that muscle. No fallen out belies.
Secondly, there's nothing wrong with strong and bulky Lats, which makes you think oh look at the arch in their back while it is the extended back, not that much actual arch in their spines.
Also, McGregor and Khabib are lining back in the pics which makes their arch more than what it actually is.
Firstly, look at all the lower abs in these athletes and see how transverse abdominal layer has straighten the waist line there, that's the reason I always recommend pulling the belly bottom towards your spine while doing abs to train that muscle. No fallen out belies.
Secondly, there's nothing wrong with strong and bulky Lats, which makes you think oh look at the arch in their back while it is the extended back, not that much actual arch in their spines.
Also, McGregor and Khabib are lining back in the pics which makes their arch more than what it actually is.

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