Plantar fasciitis is especially common in women who often wear high heels. Halvorson recommends wearing lower-heeled shoes and—when you just can't skip the high heels—purchasing good orthotic inserts with sturdy arch support. (It also helps to wear the right sneakers; check out our 2013 Sneaker Guide and find the best ones for you!)
Mistake: You're a slave to one type of workout
Why it's bad: Your knees may suffer.
Any body part is at risk when you overtrain, but knees are especially injury-prone, says Halvorson. Knees can cave in toward the center of the body, especially when running, and put pressure on the knee joints. Using orthotics in shoes can help prevent your arches from collapsing and putting additional load on the knees.
"It's very important to vary workouts and cross-train," says Halvorson. If all you do is run (and run and run), over time, soft and hard tissue structures start to break down faster from all the repetitive strain. (If you're not strength-training, find out the 9 Reasons Every Woman Needs To Lift Weights—then head to the dumbbells!)
Mistake: You pick up where you left off after a break
Why it's bad: Your back may rebel.
Even if you killed it in Zumba three months ago, don't assume you can jump back in if you've taken a significant hiatus. Why? Chances are that during your break, your core strength was reduced, and a weaker core—paired with sitting down for extended periods of time—is the typical cause of back pain, says Halvorson. Your deep abdominal tissue ends up not being strong enough to support the spine, and the hips and butt muscles aren't strong enough to hold the pelvis in a neutral position.
Halvorson suggests easing back into things by strengthening and developing your core muscles and glutes. Try bridge moves and plank exercises to work your back and core, and move around as much as possible throughout the day to prevent back pain.
Mistake: You don't properly fuel your workout
Why it's bad: You'll tax your immune system.
When it comes to your health, think of your body as a computer: Many systems run simultaneously, and your brain prioritizes them according to importance. "The immune system is secondary to heart functioning, so if you're not eating enough, your natural immunity is at a lower ebb," says Dr. Kleiner.
Plus, a Georgia State University study found that when you don't eat enough calories, your metabolism actually slows down and you burn fewer calories. Take the guesswork out of proper fueling with these 20 Perfect Workout Snacks.