When it comes to your body, knowledge is power. Literally. The better you understand your muscles and what they're capable of, the more you can do with them, whether you're acing a serve or turning heads at the pub.
But when there are about 650 muscles and millions of individual fibers to get intimate with, it's more than a little daunting. So we're going to keep it simple. Here's what you need to know to get the most from your muscles.
Let's start with the basics. You have three types of muscles: the cardiac muscle found in your ticker, the smooth muscle that lines such organs as your stomach and esophagus, and skeletal muscle, which attaches to your bones via tendons.
Skeletal muscles are the ones you use to suck in your stomach at the beach or load a new plasma TV into your car—in other words, the kind that you're most aware of as you go about your day. They make up 30 to 40 percent of your body mass and are largely voluntary, meaning you make them move—minus the occasional involuntary blip when someone scares the crap out of you.
Grow What You've Got
How many muscle fibers you have was determined by the time you dumped your middle-school boyfriend. "The number may increase early in life, but it becomes set at puberty," says C. David Geier Jr., M.D., director of sports medicine at the Medical University of South Carolina.
What you can control: how big the fibers get, which determines how tight and strong you look.
Hurts So GoodWhen you cut your finger, your body heals, but it often overcompensates by leaving a scab. Something similar happens with your muscles. Hoisting a barbell—or a baby—can cause microscopic tears in the fibers.
As a result, your muscles send a signal to nearby cells to swoop in. The cells trigger the formation of proteins at the "boo-boo" site, and that increases the size of the muscle. After weeks of dedication to a solid workout, you'll see results. (The day after a brutal workout, exercising might be the last thing you want to do—try these 5 Ways to Ease Sore Muscles instead.)
All muscle fibers are not created equal. Slow-twitch fibers are like your mom's speed-walking club: they're perfect for endurance but don't pack a lot of power. Fast-twitch fibers do the opposite: they offer bursts of rapid-fire energy, but only for a short time.
Your genes control how much of one type or the other you have. If you're looking to jack up your endurance for a marathon, hone your slow-twitch muscles by lifting 2 to 3 sets with lighter weights, pumping out 12 to 15 reps, suggests Jason Conviser, Ph.D., an exercise physiologist at the Center for Partnership Medicine at Northwestern Memorial Hospital in Chicago.
If you want to improve your 5K kick, try cranking out 2 to 3 sets of 6 to 8 reps at a heavier weight.
Your Muscle Has An IQ
When you fire a power punch in kickboxing class, your brain sends a signal down a nerve cell, telling certain muscle fibers in your arms, back, core, and legs to contract.
After a series of microscopic chemical reactions—bam—you deliver the KO blow. As you practice, your brain and muscles learn to communicate more efficiently and you become more coordinated.