The Better Sex Workout
For lower body power
Try: Ball-wall sits
Certain positions, like you straddling him, can exhaust your glutes, quads, and hamstrings. To go the distance, Los Angeles–based personal trainer Nancy Krank prescribes this "wall sit."
Place a stability ball against a wall and lean back on it so the top of the ball hits the small of your back, but still touches your lower back and tailbone.
Place hands on knees, shift weight onto heels, and, with back touching ball, begin to squat down until thighs are parallel to floor (keep knees behind toes). Hold for 15 seconds, stand back up, rest for 30 seconds; repeat 5 times.