While strength training will increase muscle mass, unless you're consuming a ton more calories, your muscles will only grow to a healthy, normal level that promotes an increased metabolism.
TRUTH: With the correct nutrition, lifting weights will result in a leaner body, not a bulkier one.
MYTH #2 'Weightlifting is bad for the joints'
This is a common misconception that weightlifting puts a harmful strain on the joints. Strength training actually helps to grow strength in the structures surrounding your joints, causing them have more support and in turn, reduce the risk of injury. Yes, you are at a chance of injuring yourself IF you use equipment that's too advanced. If you're a beginner to weight training, start small and gradually build up your weights.
TRUTH: Weightlifting PROTECTS the joints by building up the muscles to help absorb shock.
MYTH #3 'Weight lifting decreases flexibility'
Weightlifting can actually do the opposite, if done correctly. Resistance training with weights improves flexibility. The exercises should use a full range of motion while using the weights. For example, a bicep curl should go all the way up and all the way down to maximise the biceps.
TRUTH: Use a full range of motion while weightlifting to improve flexibility.