DS(3.9yo) is in his second session of soccer.
Both my kids have lower endurance. Both have had full cardio workups due to family history and were fine. We put it down to low tone, although I may have my daughter tested for asthma, as apparently she breathes really hard when playing tag with her friends.
My aspie also has much lower endurance than his peers. I think Paula is right, the low muscle tone and core body strength play a role. I also wonder if the fact that he has a very low tolerance for discomfort comes into play too. He has difficulty just standing sometimes and is always looking for a place to sit down when wee wre out and about.
I've been concerned about my 5 yo endurance lately, because of his performance at soccer games too.
My aspies have lower endurance, but I've also noticed that they frequently hyper-focus on a symptom they experience.