The hip joints house a lot of physical and emotional tension -- especially for women. The reason? Chalk it up to a combination of a sedentary lifestyle and nonstop stress. Practice these three hip stretches and strengtheners to increase flexibility -- and stave off stiffness and injury down the road.

While men may have a physical disposition for upper-body power, that doesn't mean women can't achieve great results, too. The secret? Rather than strengthen the arms in isolation, work the body as a whole, using the core and upper body together.

Sweat through an ab workout and you want nothing short of rock-hard results. But did you know that by engaging these muscles, you do more than sculpt a bikini-ready bod? Considered your vital center in yoga, your core is critical to overall health.

This exercise strengthens abdominals and obliques.

You already have all the complex, high-tech machinery you need to get into shape: your two legs. Walking works the major muscle groups of the body, raises your heart rate, burns calories, and lowers your blood pressure with a third of the impact running has on your joints.

Add these key exercises to your routine and you'll not only improve strength and balance, but also make strides toward preventing knee pain and injury.