Muscles are your body’s movers and shakers. They let you do everything from climbing a flight of stairs to chewing on a piece of beef jerky. But despite their obvious importance, most people have a rather strange way of treating their muscles. Some of us head to the gym and strain them for hours (mostly the stair-climbing muscles, not the beef jerky–munching ones). The rest of us spend more time worrying about other body parts—like the heart and the brain—and assume that our muscles will quietly adapt themselves to the demands of our day-today lives.
This is unfortunate, because the health of your muscles is vitally important to the health of your body. Even if your idea of a marathon is watching 12 back-to-back episodes of Gossip Girl, and the only powerlifting you do is moving groceries from the backseat of your car to the kitchen, you can’t afford to ignore your muscles. Strong, well-maintained muscles improve your blood pressure, your bone mass, and your ability to burn calories. They also reduce your likelihood of injury and the risk factors for countless diseases.
Meet Your Muscles
From a biologist’s point of view, a muscle is a tissue that contracts. Your arm muscles contract to swing a racket and propel a ball across a tennis court. Less glamorously, the muscles in your lower intestine contract to ropel Sunday breakfast down your digestive tract. And if you’re a woman about to give birth, your uterus muscles contract to do something truly miraculous—squeeze a brand-new person out into the world. All these examples have a common theme: when muscles contract, things happen. Even if you think you’re neglecting your muscles, they never truly get a moment’s rest. Right now, for example, they’re hard at work on a thousand small but essential jobs—pumping blood through your arteries, directing your eyes over the words in this sentence, and keeping your body from slumping over onto the floor.
Part of the reason muscles work so well is because your brain keeps them busy all the time with tiny, partial contractions called muscle tone. This activity ensures that your muscles are healthy and always ready to act. If your brain stops doing its job—which can occur, for instance, in the event of a spinal injury—your muscles become floppy and begin to waste away.
The actual biochemical process that triggers a muscle contraction is quite complicated and, like all chemical reactions, it’s not entirely efficient. In fact, as much as 60 percent of the energy that fuels your muscle movements escapes as heat. That’s why the quickest way to warm up on a cold day is to jump up and down. It’s also why your body forces your muscles to start contracting when your body temperature drops—a phenomenon we call shivering.
Source of Information : Oreilly - Your Body Missing Manual