Woman running a marathon

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The Goal That Could Sideline You in a Race
Expect: Motivation to work out; a faster pace
Avoid: Overuse injuries
Competing against your fellow gym junkies has lost its thrill, and you feel ready to take on a few hundred other runners in an outdoor race. But many participants (not just first-timers, either) increase their mileage too quickly (say, going from two to three miles on the treadmill several times a week, to four to five miles outside every morning), leading to injuries like hamstring strains, tendonitis and shin splints.
Do it right: Assess your shoes and keep in mind that pavement is harder on soles than the treadmill's rubber belt. If it's time for an upgrade, you'll want to break in your sneakers long before you get to the starting line. Then, "set a reasonable goal for your skill level and take small steps toward achieving it each day," says fitness guru Bob Greene. This means finding a training plan (here's one that will help you finish a 5K in six weeks) and maybe joining a running group.

Read more: Bob Greene on the fitness goals you should skip