Surprise risk: The beauty of walking is that unless you're doing it with your eyes closed in the middle of a freeway, it's pretty hard to hurt yourself. But it's not impossible, Matthews says. She often sees over-enthusiastic walkers trying to increase their calorie burn with hand or ankle weights. Hand weights heavier than three pounds put stress on wrists, elbows and shoulders, and ankle weights throw off your gait, which can lead to knee problems.
Ouch! Factor: 3, but the soreness might not set in until after you reach your destination.
Stride safely: Matthews suggests a vest, which is unlikely to affect your balance or gait, with weights that are 5 to 10 percent of your body weight (that would be 7.5 to 15 pounds for a 150-pound woman). Bonus: Walking with a vest not only burns more calories but also helps strengthen your bones.
Read more: Bob Green's favorite bone-building exercises