Todays Alpha males are MMA/Jits fighters not meatheads who gas 15-30 seconds after raising their heart rate. This aint the 80/90s bro.
Is this some kind of thing bodybuilders inhale? How does it work?
The sentence is saying that today's MMA/Jits fighters are much more physically fit and trained than "meatheads" of the past, and thus don't "gas out," or "run out of gas [energy]" as quickly. "Gas" comes from shortening "run out of gas."
It is common in martial arts, mixed martial arts, MMA, etc. to say something like:
"I gassed out too quickly; I must not have trained hard enough."
"If you are gassing during [insert event], then you may need to [insert advice]."
You could use "becoming fatigued," "running out of/running low on energy," and "running out of steam" in the same way.
"gas" is actually not JUST becoming fatigued, though that is the result. It involves the physiology of gas exchange at the cellular level, with oxygen being required by the muscles, but only enough being provided by the body to supply minimal function. When someone is gassed in mma, they literally cannot recover with a few deep breaths and a sit between rounds. It's a metabolic state, and they are likely to lose that fight.