1) Cardio is better for fat loss than weight lifting.
When you're trying to shed body fat your biggest concern should be reserving as much of the precious muscle tissue you have already. Why? Because the more muscle mass you possess the greater amount of calories you will burn on a daily basis, therefore if you lose a bunch of muscle while dieting you will have made it harder for yourself in the future to keep the fat off. Cardio is great for the heart and lungs and it will burn calories however, a programme that prioritises calorie control and muscle preservation through correct training and nutrition is far more important than how much cardio you can squeeze in to a week.
2) Lifting weights makes women look big and bulky.
This is absolutely true IF, that woman happens to be using anabolic steroids, otherwise it's just not going to happen. Competitive female bodybuilding has somewhat cast a dark shadow over weight training for women however you must bear in mind that the average male produces up to ten times the amount of testosterone than the average female, making it far easier for men to build muscle than females (unless you're using steroids that is). So know this, if you want to shed body fat, move better, and get healthier, stop worrying about 'bulking up' so much and cast this old myth aside, FAST!
3) Muscle turns into fat and visa versa.
I can't even begin to imagine where on earth this one comes from but sure enough it's been floating around for a while and every so often rears its dirty little head. The myth being that if you build muscle but then neglect to use it, it will turn into fat, and/or, when you lift weights your fat magically morphs into muscle. I'm fairly sure I don't need to spend too much time on this one except to say that yes. if you neglect to maintain the muscle you've built through consistent training and suitable nutrition your muscles can atrophy (reduce in size and strength) however, muscle tissue cannot undergo metamorphosis to become fat tissue. Like wise, muscle is built through specific training and the proteins we consume in our nutrition, it is not built using our fat stores.
4) Being sore equals a good workout.
Any old monkey can put a client through the ringer and have them walk out the gym like they've been hit by a car, it can be done in five minutes. Muscle soreness is simply a reaction to a stimulus to which we are not adapted and should not be confused with the marker of a good workout. An effective training programme should address mobility, flexibility, movement and the strength and health or skeletal muscle and joints. Yes. sometimes you will be sore but know this, (I've said it before) if you walk out of every session feeling like you've been hit by a car, you have yourself an ill-educated and misguided trainer at best.
5) Sit ups and crunches build a strong core.
This is a personal favourite of mine, it's everywhere, all over the youtubes and webbernets... hundreds and thousands of so called 'fitness and strength professionals' pedaling this tripe about how sit ups, crunches and pretty much any other kind of gym circus trick they can dream up will build you a strong 'core'. Utter, utter NONSENSE!! Let's define the 'core' very quickly for the purposes of this point. Your core consists of far more than just the six-pack mirror muscles at the front of your abdominal area, there are also your spinal erectors, gluteal complex, obliques and transverse abdominals to name a few. All of these muscles combine to stabalise your spine and in order to strengthen them there some very specific moves that will do so very effectively. Banging out hundreds of sit ups will make you very good at, well, doing sit ups (flexing the spine), this is great if for some reason you need to repeatedly sit up from a lying position but not much good if your goal is to create a stable environment for your spine. Compound lifts and their derivatives such as the squat and deadlift are paramount for building a super strong core. these lifts demand your entire body to utilise all of its musculature in order to stabalise and keep your spine in a neutral position throughout the lift, this combined with sufficient stimulus and effective programming will build a strong core, circus tricks will not!