Your girlfriend complains she's been struggling with cardio, and hates mindlessly running on the treadmill. But this is all an excuse to have more strap-on sex...which you're not opposed to. The warmup consists of you sucking her strapon, warming it up in your mouth, getting it nice and wet for your hole. Once you're fully warmed up and throbbing for it, she climbs on top of you and begins pegging you. She's going to keep thrusting until her muscles give out.
