Give your leg muscles

Just three 20-second "sprint" intervals -- running or cycling, for example -- seem to offer about the same benefit as a 50-minute jog. Even with the warmup, cool down, and rest between intervals, that's just 10 minutes of your time, compared with almost an hour for a run. Ask your doctor if you haven't exercised in a while, and start slow.

Don't want to deal with hot or cold weather? Indoor games can get your competitive juices flowing, like basketball, racquetball, or volleyball. You can do many "outdoor sports" -- like swimming, soccer, and tennis -- indoors, too.

If you like to be outside but don't want to commit to a league, head to the park and join a pickup game of whatever's going on: soccer, Ultimate Frisbee, touch football. Even playing catch will get you moving around.

Whatever your interest or skill level, there's probably a sports league in your area that will work for you. You'll be less likely to skip out because your teammates will count on you for practice sessions and games. And the heat of competition could make you forget you're getting a workout.

When you need to talk with a co-worker, hit the trail (or sidewalk) and kill two birds with one stone. You'll get some exercise,and it might also make your meeting more creative. Just keep it to no more than two or three people. More than that can make it hard to really engage.

It can be social, and it's lots of fun, even if you do it by yourself. It can tone your muscles and strengthen your heart and lungs. It also might lift your spirits. All you need is a bit of music to get your groove going.

If you like to take walks with a purpose, look online for secret "geocache" spots in cities, parks, or along hiking trails. You follow clues, usually GPS coordinates, to track them down. You could find a prize in the cache or sign your name in a journal that proves you were there.

You'll burn around 5 calories a minute, about as many as with a brisk walk. And you'll use about the same amount of oxygen as if you were raking leaves. Plus, research shows that it may help prevent heart disease, though that only seems to be true if you’re in a healthy relationship.

You might not think of it as exercise, but if you dig, bend, and clip around your garden for 30 minutes or so, you'll get a decent workout. And it may even put you in a better mood. If you don't have a plot of your own, consider volunteering at a community garden. They can probably use the help.

Want to get two things done at once? You'll get a "moderate" workout if you wash and wax your car, clean out the gutters, or mop or vacuum the floors. It'll help get you in better physical shape, and a clean car or house may boost your mental well-being, too.