Working out your chest probably isn’t the first thing on your to-do list in the gym—but maybe it should be. Your chest muscles (a.k.a., pectoral muscles or "pecs," which are some of the largest in your body), are responsible for your upper body's stability, helping you to maintain proper posture, and even play a part in your ability to breathe deeply. Plus, they help you tackle everyday functional tasks like pushing open doors or picking up groceries.

Over the next 21 days, expect to tone those chest muscles, increase flexibility, and possibly even give your breasts a lift (breast tissue sits on top of the pectoral muscles, FYI) with these 17 strengthening and stretching moves. Get started and put your best chest forward.

Isometric Chest Squeeze

Stand tall with one foot slightly in front of the other and a dumbbell in each hand. Bend elbows, bringing weights in front of chest. Lift dumbbells so your elbows are slightly above your shoulders, squeeze weights together and hold.

Standing Press

Stand tall with your feet shoulder-width apart and a dumbbell in each hand. Bend your elbows, brining arms out to sides to form two 90-degree angles. Maintaining this position, bring arms/weights in to touch. Return to start. This is one rep.

Standing Hands Above Head Stretch

Stand tall and place hands lightly on the back of your head, fingers interlocked. Gently squeeze shoulder blades together as you pull your elbows and hands back, and hold.

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Lying Dumbbell Chest Press

Lie faceup with knees bent and feet flat on the ground. With a dumbbell in each hand, extend arms straight up, palms facing out. Slowly bend arms, lowering them to your side until your elbows nearly touch the ground. Reverse movement to return to start. This is one rep. Note: For Day 8, legs will be in table top position.

Lying Dumbbell Chest Fly

Lie faceup with knees bent and feet flat on the ground. With a dumbbell in each hand, extend arms straight up, palms facing in. Keeping a slight bend in elbows, lower your arms out to the sides of your body until your hands are about six inches off the ground. Slowly reverse the movement to return to start. This is one rep. Note: For Day 8, legs will be in table top position.

Sphinx Pose

Lie facedown with legs hip-width distance apart and forearms on the ground. Press into forearms and lift head and chest off of floor as you squeeze thighs and butt, and press the pubic bone into the ground; hold.

Hand-Release Pushup

Get into a straight-arm plank with hands under shoulders, feet hip-width apart, and core tight. Lower body until your chest touches the floor. Retract your shoulder blades and lift both hands off the floor. Place hands back on floor, and then push back up to start. This is one rep.

Wide-Grip Pushup

Get into a straight-arm plank with hands slightly wider than shoulders, feet hip-width apart, and core tight. Bend elbows, lowering body until your chest nearly touches the floor. Push back up to start. This is one rep.

Sitting Chest Stretch

Stand tall, with fingers interlaced behind your back and near your butt. Keeping your back straight and shoulder blades together, push your arms up until you feel the stretch.

Lateral Lunge to Chest Press

Stand with feet shoulder-width apart, toes pointed forward, and a medicine ball in hands at chest level. Take a large step out to the right with your right foot as you drop your hips down and back while keeping the left leg straight. Simultaneously press the medicine ball straight out in front of you. Press into your left heel to rise back up to standing position as you simultaneously pull the medicine ball back in to chest. Repeat move on the other side. This is one rep.

Medicine Ball Chest Throw

Stand facing a wall about six feet away with a medicine ball in hands at chest level. Explosively pass the ball from your chest to the wall as hard as you can. Catch the ball on the rebound. This is one rep.

Wall Stretch

Start in a split stance with left leg in front of right at the end of a wall. Bring the right arm up to shoulder height and place the palm and inside of the arm on the wall. Gently press the chest through the open space to feel the stretch and hold. Repeat the move on the other side.

Lying Dumbbell Chest Press Variation

Lie faceup with a dumbbell in each hand, palms facing forward, and feet flat on ground. Lift arms straight up so the dumbbells are in line with shoulders. Keeping left arm lifted, lower your right arm down until your elbow is even with your shoulder. Lift the right arm back up to start and then lower the left arm while keeping the right arm straight up. Lift the left arm back up to start. Lower both arms, and then press back up to start. This is one rep.

Inchworm to Pushup

Start standing with feet hip-width apart. Hinge forward at your hips and place your palms on the ground. Walk your hands forward to come into a straight-arm plank. Bend elbow and lower chest down to perform on pushup. Push back up to high-plank and then walk hands back in toward feet and stand up. This is one rep.

Dumbbell Pullover

Lie faceup, holding one dumbbell overhead with both hands. Press the weight over your chest, then slowly reach back over your head, continuing until you feel a stretch in your lats. Next, slowly pull the dumbbell back over your chest. This is one rep.

Kneeling Medicine Ball Throw

Kneel facing a wall about six feet away with a medicine ball in hands at chest level. Explosively pass the ball from your chest to the wall as hard as you can. Catch the ball on the rebound. This is one rep.

Lying Pec Stretch

Lie facedown with arms out to sides so your body forms a "T." Pushing off the ground with your left hand, slowly roll your weight onto your right side. Lift your left leg, bend the knee, and place the left foot behind you on the floor for stability; hold. Return back to start and repeat the move on the other side.

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These Chest Exercises Will Totally Transform Your Upper Body in 21 Days