Let's say you stay active, to some degree, most days of the week. Then one day you decide to call it quits for one reason or another. Maybe it's an injury, work, a relationship or sheer boredom. Regardless, you hang up your running shoes and close the drawer on your workout clothes for good. What consequences will your body suffer as a result of your sedentary life?
Muscles get smaller: A lot of people think their muscles will just melt away and turn to fat if they stop using them. Actually, muscles can't turn to fat, but they can get smaller - a lot smaller. When you stop doing weight bearing activity on a specific part of your body, the muscles in that region of your body will atrophy. As muscles atrophy, or shrink, your metabolism slows down. As your metabolism slows, your body requires less energy (aka calories). If you don't compensate for the difference, you'll put on weight.
Technically, walking is a weight bearing activity - and good for people to do. But if you go from walking up a steep hill for 30 minutes every day to walking on a straight road for 30 minutes every day, chances are you could lose some muscle in your legs and bottom. For the most part, you'll also experience some atrophy if you go from doing three sets of heavily-weighted squats to doing the exact same number of squats, but using much less weight.
Lung capacity gets smaller: Your little two-week break from exercise has turned into two months, and now your gasping for breath walking up a flight of stairs you would normally scurry up with ease. When we go from regular cardiovascular activity to very little or none, the demands on our lungs are not as great, thus the capacity - or space for oxygen - is less. The benefits of cardiovascular activity reach far beyond our lungs, into our hearts and the muscles that bear the weight of the activity we do. Fortunately, for those of us who have taken a sabbatical from regular work out for good reason (pregnancy/child birth, illness/injury) can expect to snap back fairly fast. You should feel 100% again within a couple weeks.
You lose flexibility: When you stop exercising, not only do muscles get smaller, but they can get tighter, too. Bending over or squatting down to get something off the floor might not be as easy as it was when you were moving around regularly. Your joints and ligaments will also suffer. If you ever run into a series of days where you can't really get in a good workout, at least take five minutes to stretch.
You'll be crabby: If you're on the verge of regular exercise, but haven't quite made the leap to regular workouts, I PROMISE YOU, you'll be so much happier when you do. Quite possibly the best benefit of exercise is how it makes you feel mentally. I think I sound a little too much like Richard Simmons right now, but it's true. Stress management, confidence...not to mention lung capacity and muscle tone all go through the roof. Endorphins are feel-good neurotransmitters that are turbo-charged when we exercise. The exercise might be yoga, a run outside, or weight lifting. Really, anything that gets your heart pumping will cause this response.
Let me be clear about one thing - activity is activity - but there is a big difference between purposeful activity and day-to-day activity. Purposeful activity is anything you do that goes above and beyond typical day-to-day activities. Day-to-day might be opening up the back door to let the dog out, whereas purposeful activity is walking the dog five blocks. Day-to-day activity might be driving to work, then taking the elevator ten floors to your office, whereas purposeful activity is riding your bike into work and walking the ten flights of stairs to get to your office. Day-to-day activity is driving six blocks to the coffee shop to catch up with friends, whereas purposeful activity is walking those six blocks instead.
If you can't fit in a structured workout, look at what you can do in your day-to-day activities. Can you walk instead of drive? Take the stairs instead of the elevator? These count greatly and add up to a lot over time.