Perhaps a better question would be what doesnt? Most of us have jobs that require us to stay seated or standing for long periods of time. If you use a computer, youre probably sitting most of the day. That means some muscles dont get exercised at all, while others do all the work. The ones that dont work get weaker. The ones that do work get stronger, but not in the healthiest way. If we dont give our bodies balanced exercise, our muscles cant work together properly. Our bodies are designed to move throughout the day.
While youre sitting at your desk, your hip flexors (hip muscles) and quadriceps (the muscles on the top of your thighs) remain for long periods in a relaxed, shortened position. At the end of the eight-hour day you stand up to walk and exercise your gluteus (butt) muscles. But aside from this simple act of standing and walking, your gluteus is not being worked. As it happens, the gluteus is the antagonistic (opposite) muscle to your hip flexors. This may be the extent of the exercise your gluteus receives in a typical day; youll walk to your car, drive home to sit in front of the television until its time to go to bed, than start the same cycle all over again the next day.
Over a period of years, your muscles begin to suffer from this neglect. Instead if lengthening when you stand, your hip flexors and quadriceps remain shortened even after you stand up. And when your hips and quads cannot lengthen all the way, your pelvis has no choice but to rotate forward as you stand, tipping your waist forward and making your butt stick out. Other things happen as well—since walking bent over isnt an option, the muscles of your lower back work to tilt your chest and shoulders back to counterbalance the effect and help you stand upright. Since you are putting unnatural strain on your spine and lower back muscles, its no wonder your back hurts. As you can see, all of our muscles are connected, and the effects of muscle imbalance are felt throughout the body.