Weights add bulk. Running gives you saggy cheeks. It’s a vicious cycle, all that vicious cycling. But it’s the strenuous attitude that’s weighing you down. Until you try Gravity Defying Fitness, an aerial-based training program Lorelei Ashe MacDonald developed around tricks she learned in the circus (check out the video of her vaudeville trapeze act). The petite yet powerful high-flyer aims to help you build strength, carve abs, and tone arms through exercises on chin-up bars, suspended rings, ropes, and tumbling mats. MacDonald loves a deadline (eight weeks till summer!) and packs her custom hour-long sessions with tests of agility, coordination, and flexibility. You’ll look like a dork doing your first roly-poly (don’t ask; just do), but the payoff is big (and you can view it from behind). She’ll be a permanent fixture as soon as The Plaza gets its act together. In the meantime, book her at Hype Gym or your gym. Enough options to cater to your theory of relativity. Gravity Defying Fitness (646-334-3036 or gravitydefyingfitness.com).