If you want to improve your posture, stretching isn't the only thing you should be doing. While stretches do help to loosen up stiff joints and muscles, you may find that your poor posture is the result of muscular deficiencies in certain parts of your body. To improve your posture, it's time to work those muscles!

Here are 6 basic strength-training movements you can do to help improve your posture effectively:

1. Plank

If you have poor posture when standing, it may have something to do with weak abs and back muscles. There are few exercises better for your core than planks, and doing them can improve your posture drastically.

To perform a plank:

Get on your hands and knees.
Step your feet back until you are in the push-up position.
Keep your hips low to the ground, your knees straight, and your head relaxed.
Hold for 30 to 60 seconds.

2. Single Leg Extension

To align your hips with the rest of your body, this is one of the best exercises around. By doing this movement, you train the muscles in your pelvis and core to work together, improving stability all around.

To perform the exercise:

Lie on your back, knees bent, with your feet flat.
Extend your legs and keep your knees straight.
Without lifting your lower back from the floor, raise your right leg until it is at a 90-degree angle to your body.
Hold for 30 to 60 seconds, then repeat with the other leg.
The static movement will do wonders for your pelvis and core!

3. Cable Pulldowns

If your shoulders are hunched forward when you sit or stand, it may be a sign that your upper back muscles aren't properly developed. Cable Pulldowns are one of the best exercises for your upper back.

To perform Cable Pulldowns:

Sit in front of the cable machine.
Grip the bar just beyond shoulder width apart.
Pull down until the bar is nearly touching your chest.
Extend your arms and repeat
Adjust the width of your grip to target specific parts of your back musculature.

4. Bridge

This is another exercise aimed at improving the strength in your lower back and hips. If you spend a lot of time in a chair, this is a good one to do!

To perform Bridge:

Lie on your back, with your knees bent and your feet flat on the floor.
Thrust your hips toward the ceiling and clasp your hands beneath your buttocks.
Hold for 30 to 60 seconds.
An easy exercise, but one that will do wonders to improve your posture.

5. Shrugs

If you tend to hunch forward when you walk, sit, or stand, shrugs will help you to focus on keeping your shoulders back, your head up, and your neck loose.

To perform shrugs:

Stand with your back straight and your head up.
Grip a barbell in your hands.
Try to bring your collarbones to touch your ears (the shrug).
Hold for a one-count, then lower.
Repeat.
To do it right, you'll need to focus on your posture, so it will help you to stand straighter.

6. Side Plank

Yet another exercise aimed at strengthening your core and developing the muscles that keep you erect and upright when standing, sitting, or walking.

To perform Side Plank:

Assume the "Plank" position (see Exercise #1 at the top of this page).
Shift your weight onto your right hand and right foot.
Raise your left hand off the ground and reach it as high into the air as you can. Place your left foot on top of your right food.
Hold for 30 to 60 seconds.
Return to Plank position and repeat on the left side.
A wicked movement to strengthen not just your abs and back, but also your obliques!