3. Always opt for cardio over weightlifting if you want to lose weight
The truth is, you need both and lifting weights/strength training builds muscles, which helps you burn more calories.
4. You must stretch before you work out
Warming up with cardio before a workout is much more effective than stretching. It will get
5. Working out longer is the only way to get fit and lose weight
Actually, the truth is; quite the opposite. Shorter, high-intensity workouts are proven to be more efficient and better for your health. Slaving away on the treadmill for hours at the same speed is not going to do help your fitness level, but cutting your time in half and alternating between high and low speeds will increase your fitness level and calorie burn.
6. If you are not really sore, you're not working hard enough
Muscle soreness is to be expected during a workout, especially if you are trying a new exercise of lifting a heavier weight, but if you're in serious pain, stop what you're doing. It doesn't mean you're working harder -- it probably means you're injuring yourself.