Squats are one of the most efficient ways to strengthen the legs because they work the quadriceps (front of the thigh), hamstrings (back of the thigh), and gluteals (buttocks) at the same time. To perform them, stand with feet shoulder-width apart, arms extended from the shoulders parallel to the ground (they'll help you balance). Sit back slowly, as if you're lowering into a seat, pause for a second, then lift at the same speed. Perform three sets of up to 24 repetitions.

Follow these tips while doing squats:

• Your chest stays lifted; look straight ahead.

• Keep abdominals tightened.

• Aim to lower until thighs are nearly parallel to floor. Hips shouldn’t drop below knee level.

• Knees and toes face forward. The knees should not extend past the toes. If they do, you’ll put unnecessary stress on the knees.

• Your body weight stays in the heels, rather than the toes.

Body Bonus
Hold a pliable gym or playground ball (about the size of a soccer ball) between your legs, right above the knees. Gently squeeze the ball as you lower and rise while performing the squat. Holding the ball builds strength in the inner thighs. It also keeps you in proper form—the knees stay narrow and together, and the hips stay back. This will make the move more challenging, but also more effective.

More great bone-building workouts:

Shoulder Press
Shape up your shoulders

Bent-Over Rows
Bent-over rows are a demanding but highly effective method for building strength in these rear core muscles.

Squats
This exercise is one of the most efficient ways to strengthen the legs.

Back Extensions
This exercise improves posture and is excellent for torso flexibility and strength, both of which reduce the risk of lower back pain.

Lateral Pulldowns
This strength move targets your upper back muscles