To get back in shape without getting injured, give yourself six weeks to build up gradually, and consider the following:
Take every other day off. A day off will give your muscles a chance to heal, which will allow you to run longer and harder during each workout. If you don't want to take every other day off, just be sure to run at an easy pace on your recovery days.
Cross-train intensely. You need to put in intense efforts to build fitness. But doing a lot of hard, fast miles in the early part of your buildup can make you sore and set you up for injuries down the road. Instead, make low- or no-impact cross-training activities such as spinning, swimming or elliptical training your most intense workouts. When you run, concentrate on endurance rather than speed, says Budd Coates, four-time U.S. Olympic Marathon Trials qualifier and fitness director at Rodale Press in Emmaus, Pa. Eventually, you'll be able to replace the cross-training activities with some intense running workouts, and your body won't complain a bit.
Walk and then run. If you haven't run at all for two months, start by walking for 30 minutes. Progress to running for 30 minutes with a one- to three-minute walking break every three to six minutes. Increase your run by five to 10 minutes each week. Eventually, if you want, you can switch to continuous running.
"The walking breaks allow you to go farther without overextending your muscles," explains Jeff Galloway, training expert, Runner's World columnist, and former Olympian.