If you're aspiring to a flat, manly chest, start by considering what you've got instead. Some guys have "man boobs," which are caused by accumulations of fat around the pectoral muscles.
Other guys just don't have much of anything in the way of pecs, so their posture sags inward to form a concave profile. Whatever the case, a full-body approach that includes diet and exercise are the best way to flatten your chest and enhance your stature and bearing.
Improve Your Posture with Yoga
Whatever type of physique you have, posture dramatically affects the way you look. Tight pectoral muscles are one of the main causes of sagging posture, which in turn cause your chest to look underdeveloped. Yoga can help.
When you open and lengthen the pectoral muscles and strengthen the muscles in your core and back, your chest takes a more forward position in your overall posture. Where the pecs were previously droopy and sad, opening your shoulders with yoga lifts and flattens them for a trimmer, leaner appearance.
Do a chest expansion pose by interlocking your hands behind your back and lifting your arms upward from the lower back to chest level. Open the chest muscles and take deep breaths into the abdomen. If your chest and shoulders are too tight to interlace your hands, hold onto a strap.
Read more: How to Build Chest Muscles for Skinny Guys
Burn Fat, Lose Weight
Guys may have "moobs" for a couple of different reasons: they've either got too much fat on their bodies overall or their pectoral muscles are underdeveloped. In most cases it's probably both.
Everyone accumulates fat in different places and we've all got squishy areas we'd like to shrink, firm up or just get rid of. For guys, upper body fat is a particular bummer, but if you've got it, you're not necessarily stuck with it.
But, just as you can't choose your family, you can't choose where to make fat go away. Even if your chest is the fattest part of your body, it's not necessarily the place that's going to shrink first when you start losing weight. There's no such thing as "spot reduction."
The best strategy is to employ both diet and cardiovascular exercise that gets your heart rate up. To lose a pound of fat, you need to burn off 3,500 more calories than you take in. Lose it too fast and you run the risk of rebound weight gain.
The National Institutes of Health recommends losing at a rate of about two pounds a week. That means you'll need to create a deficit of about 1,000 calories a day to lose two pounds a week. This can be done by upping the amount of calories you burn with cardiovascular exercise such as treadmill, jogging or stairs and by reducing calories.
Whether you're overly padded or underdeveloped with a "sunken" chest, you'll benefit from building up not just your pectoral muscles but also the rhomboids, traps and posterior delts. When these upper back muscles are weak, they allow your posture to round forward.
Push-ups are a great all-purpose exercise that work a number of muscle groups in addition to the pectorals -- from the back of the neck as well as the muscle groups in the shoulders, core and back.
Push-ups help with tone, but there are many benefits to adding muscle mass by hitting the gym. For one thing, muscle burns more calories than fat, so adding it will boost your resting metabolism.
You build muscle mass when stress inflicts the muscles with tiny tears and injuries; this then stimulates muscles to rebuild and repair themselves. And that is best accomplished with some heavier lifting.
According to a study by the American Council on Exercise, the three most effective chest exercise are the dumbell bench press, the pec-deck machine and bent forward cable cross-overs. But remember that a strong core is essential to your overall strength and balance, so avoid overdoing pec exercises at the expense of your core, back and limbs.
Read more: Are There Exercises to Flatten a Big Chest?