Well after all those episodes of Friends (and those countless reruns), it's probably because we feel we know Jen so well - so maybe we'd trust her to turn up and motivate us when we the last thing we want to do is exercise.
"You can see why Jennifer Aniston was voted top workout partner," says Kirsty Kothakota, a spokesperson for Shock Absorber. "She'd inspire you with her dedication and discipline, the incredible results she achieves and you'd have a good time working out with her too."
It's pretty good timing for the actress, whose latest movie, Just Go With It, was released in the UK yesterday.
Second on the list of celebs to get sweaty with (in an exercise sense, naturally) is Coleen Rooney, followed by Madonna in third place. Though if you ask us, most mere mortals would have a hard time keeping up with Madonna - but there's probably no one better for making you stick to achieving your goals.
Friends are a huge part of keeping women motivated where exercise is concerned, the survey also found. Eight out of ten women said their mates were the most significant motivating factor when they need inspiration to keep going in terms of exercise, while 90% said they like to train with someone who has similar fitness goals.
What would it take to get you to exercise regularly (and if you already do, what's your secret)?