If you've seen a lot of the comments, people have issue with them casting an already thin woman when it's exercise equipment. There's nothing wrong with her, as a person, but as someone who IS overweight, it comes across as them not wanting to appeal to customers who might want to use the machine to lose weight. Which, maybe they are okay with that! I personally would have had less issue with the ad if the person featured in it was easier for me to identify with, and I'm sure that's the case for others as well (note how a lot of the jokes about the ad are people saying "oh man, starting my tough life-changing journey to go from 115 to 112, pray for me!").
But again, they are JOKES about an AD about a FICTIONAL person for an OVER-PRICED piece of workout equipment.