Intermediate

We all know what this position entails, right? She's in front of you on her hands and knees; you're behind her on your knees, holding onto her hips. In this position, you need to be able to stay balanced on your knees, while thrusting back and forth. What will help you most with this? Core strengthening.

Exercise: Crunches

Crunches. Oh yeah, it's time to focus on your abs. You might think she can't appreciate your 6-pack if you're behind her, but make no mistake-even if she can't see the results of your crunches, she'll be able to feel it. Press your back on the ground with your knees bent, keeping your feet against the floor. Lift your head and shoulders off the ground, keeping your head in line with the rest of your body. You want to envision a tennis ball or an orange between your head and your chest. Lift up. Make sure this movement originates with your abs - don't use your neck or your hands behind your neck to help lift you up.