1. You'll Improve Your Posture
When it comes to posture, the back and shoulders get all the attention. However, as one of the largest muscles in the upper body, the pecs play an equally important role in maintaining posture and upright stability, namely by supporting the scapula (your shoulder blade) and the shoulder joint itself.
"Every muscle that surrounds the scapula and shoulder is going to be important for stabilizing those joints," says Joel Seedman, Ph.D., exercise physiologist and owner of Advanced Human Performance in Suwanee, Georgia. "If one gets weaker, then you will have offset tension across the joints."
And if one muscle becomes overly shortened or lengthened, it won't matter much if they're strong or weak—the pecs won't be able to sufficiently do their job. The biggest culprit of shortening? Your computer. When you slouch over it all day, you
simultaneously shorten your chest muscle fibers and lengthen your back ones, says Seedman.
To help counteract that, try performing a basic chest exercise two times per week for three sets of 6 to 10 repetitions. Grab a weight that's 10 to 20 percent less than what you would normally use (so, if you typically press 60 pounds, use 45 to 55), and perform a chest press. When you do, spend three to four seconds lowering the weight (also known as the eccentric phase of the exercise), and then hold that bottom position for another three or four seconds before driving the weight back up. "That accentuation of the eccentric phase helps to make sure that the pec muscles stay in their optimal lengthened state," says Seedman. It also ensures that your shoulders and scapula also stay in their proper position, as opposed to becoming rounded and slouchy.
2. You'll Breathe Easier
When you fix your posture, you also open up your chest, which makes it easier to take deep, quality breaths. The pec minor in particular is especially helpful, as the smaller, triangular muscle attaches at the middle of your third, fourth, and fifth ribs. Any time you breathe in, the pec minor stretches, allowing your ribcage to expand.
"If the pec muscles are overly shortened, then breathing will be significantly impaired because you're not going to be able to open up the diaphragm," says Seedman. "But if you're lengthening those chest fibers, breathing and the ability to improve oxygenation to all your muscles is going to be greatly improved."
3. You Can Make Your Breasts Perkier (If You Want)
Seedman says many women shy away from training their chest because they think their breasts will shrink, but that's actually the opposite of what can happen—chest exercises are kind of like a non-surgical method of breast augmentation. "What you're doing is pushing the breast tissue up and forward more, so it gives the illusion that your breasts are bigger," he says. Plus, adding muscle to your chest helps elevate your breasts, "almost acting like a push-up bra." And don't forget: Adding muscle beneath the actual breast tissue doesn't take away from the breast tissue itself.
4. You'll Make Daily Living Easier
Outside of the gym, your pecs play a major role in a wide variety of daily activities, from loading grocery bags into the house, to pushing open a heavy door or lugging a suitcase around an airport. "Pretty much any upper-body activity or motion that we do involves the pectoral muscles to a significant degree," says Seedman.
The primary functions of your pecs are to flex (raise), adduct (bring back), and medially rotate (turn inward) your upper arm. So, "if you think of picking things up, holding things, squeezing things, or any kind of movement that involves pushing, the pecs are involved in all of that," says Thomas.
That's why, if your pecs are weak from disuse, the simple act of carrying and loading grocery bags into your house can feel like a challenge. From a purely functional standpoint, you'll make your day-to-day way easier if you regularly train your chest muscles.