I have heard college football announcers today comment on players being large, strong, muscular, short, large hands, long limbs, light, tall, oversized, powerful. and undersized. There were probably more that I didn't pick up on.
The hesitation before using the word 'muscular' indicates that it was a euphemism, but not for fat, more like a comment on the posterior of the pacers, and the instagram you mentioned really bears it out. He wanted to say that they were attractive and womanly in some way that the distance runners weren't.
He's right, most elite distance running women have lost their period, are infertile and have disastrous hormonal problems.