ONE. Exercise will undo bad eating habits.
You cannot outrun a bad diet. It takes 60 seconds to eat 300 calories and it takes 30+ minutes of running to burn 300 calories. See the problem?
TWO. Soreness is an indication of a good workout.
Weight training causes micro-trauma to your muscles. A little soreness after your workouts is normal and sometimes inevitable, but your ultimate goal should not be to be sore after your workout or the next day. Extreme soreness is an indication you've overstretched.
THREE. Cardio is the best way to lose fat.
Contrary to popular belief, cardio doesn't burn that mean calories. Building muscles is the best way to burn the most amount of calories every single day. Cardio likely isn't sustainable either; you're likely to get bored of it and like all exercise, your body will adapt so you'll have to do more and more to keep seeing results.
FOUR. I can spot reduce fat (i.e. doing crunches will get rid of stomach fat)
Unfortunately, you cannot choose where you lose fat from. You're genetically predisposed to carry fat in certain places and, therefore, genetically predisposed to lose fat from certain places before others as well.
FIVE. The more I do, the better.
There exists an optimal amount of exercise for your body. Any less or any more will get you to your goals slower. Consistency is vital to your success and in order to be consistent, you must choose a routine that is sustainable for your lifestyle. You will burn out and lose motivation very quickly if you have the-more-the-better approach.
SIX. Lifting heavy will make me bulky.
Weight training does one thing very reliably: it makes you stronger. The truth is, the "toned" look you're likely after is in fact obtainable only from building muscle. "Bulky" might happen if you take steroids, become one of the world's strongest women, and eat 5,000 calories a day. Becoming bulky is truly the least of your concerns.
SEVEN. Women should train differently than men.
Muscles aren't male or female. They function the same way in every body. The weight you may use compared to men may differ, but the exercises, the sets, the reps--us women can and should be using all of the same training modalities.
EIGHT. Running is better than walking.
I used to think I had to be a runner if I wanted to lose weight. The problem is, I hated it. So why would I make myself do something I hate? SUSTAINABLITY IS KEY. I'm willing to bet that daily walks are far more sustainable for you than daily runs. Walking is so incredibly powerful. Never underestimate it.
NINE. I can eat unlimited amounts of "healthy foods".
Just because a food is deemed "healthy" doesn't mean you can eat copious amounts of it. Let's take almonds for example. They are generally classified as a 'health food'. One almond has 7 calories. Think about how easy it is to eat a handful of almonds. For the sake of this example, let's day a handful is 30 almonds. That's 210 calories. Do you see how quickly that adds up?
TEN. Deadlifts are bad for your back.
Deadlifts strengthen your back. They can actually be effective for treating lower back pain. If a movement is uncomfortable, you should ask yourself why. Your body should be able to preform this everyday movement. Like any exercise, deadlifts can be dangerous if they're executed with bad form.