Stretching before your work could actually be counterproductive to your muscles because your muscles need to be warmed up before they can stretch out. Think of your muscles like a rubber band that has been in the freezer. It won't stretch very far right away. Your warm up time is used to get your muscles ready to work and stretch. Cold muscles are also more prone to injury because they are unstable. Save your stretching for after your workout.c 

Men have 20-30 percent more testosterone than women, so their bodies react differently to weight training. When men lift weights, they gain muscle mass, but when women lift weights, their muscles tend to tighten and lengthen. Also, the more muscle mass you have, the more fat you are burning throughout the day. It also increases bone strength and is good for your overall health. The only way for a woman to bulk up like a man is to take steroids or to be weight training five hours every day. Thirty minutes a day three times a week is all you need for toned muscles.c 

While you may burn slightly more calories by using weights while on the treadmill, the risks outweigh the benefits. You won't be as focused on what you're doing, putting you at risk for joint injury. A better way of increasing your caloric burn is to increase the incline on the treadmill or increase the resistance on the elliptical, then do your weights once you're done with cardio.c 

1. Myth: Crunches with flatten your stomach. Truth: Cardio plus dynamic ab exercises will reduce abdominal fat, making the underlying muscles more visible.c 
2. Myth: You can turn muscle into fat. Truth: At any given point, you are either losing fat or building muscle, but not turning one into the other.
3. Myth: Exercising once a week isn't worth it. Truth: Something is better than nothing.
4. Myth: You can "spot reduce" trouble areas like love handles or inner thighs. Truth: Your body has a pre-determined way in which it will lose weight, so do cardio to reduce fat overall and weight train every major muscle group. Eventually, you'll be fit all over.
   
5. Myth: No pain, no gain. Truth: Pain is an indicator that you're doing something wrong. Soreness, on the other hand, means you're working muscles that you previously haven't.c