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?
I believe the author is talking about losing their energy after a short period of time
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.