In a way, the missionary position is the physical equivalent of the old "I'm busy washing my hair" excuse—it's the brush-off used when you're lazy, tired, or just not that interested. But despite being one of the most passive contortions, this position can still make for pretty good workout sex. It actually will start burning. Patti Britton, author of The Art of Sex Coaching and immediate past president of the American Association of Sexuality Educators, Counselors, and Therapists, agrees that you'll definitely be feeling it in your abs. That's where women tend to get stuck—they tend to rely on their lower back to give them propulsion.

Sure, sex is a type of workout in its own right. A small study found that sex burns about 4. The same study showed that 30 minutes on a treadmill burned more calories: calories for men and for women. But for more feel-good sex, science is pointing fingers at burning calories at the gym first. Just as it would during a gym session.

Try any or all! Lunges boost flexibility, so he'll be able to find your G-spot in almost any position. Do the move: Stand with your feet spread wide, about twice shoulder-width apart, your feet facing straight ahead. Bend slightly at the waist, and clasp your hands in front of your chest.