When people think about muscle, they think biceps, triceps, glutes, and abs. But beyond the muscle you can gawk at see, there's a lot of muscle that's in action all the time inside your body -- like your heart, for one. So, even if you're not trying to build rock hard abs, it's important to remember to feed the muscles you can't see too.

Protein is important to muscle health, because it contains amino acids necessary for growth and repair. According to MSNBC, most Americans get plenty of protein in their diet, but tend to eat less of it as they get older. But not only is the amount of protein you eat important, so is it's quality. Choose high-quality proteins like eggs and fish over fattier meats like ground beef.

Protein isn't the only nutrient necessary for strong muscles. Find out what else you need over at MSNBC and in the gallery below.