Myth # 1

It is possible to do spot-toning through resistance training 

Building muscle is extremely exercise-specific.  Only the muscles that are exercised through progressive reisistance experience a training effect of increased size, endurance, or strength.  However, reducing fat in a certain area (e.g., the abdominals or thighs) through exercise-specific training is a myth.  Performing 1000 abdominal exercises a day will not create "toned" abs.  Muscular strength and endurance will certainly improve, but to get a "toning" effect, the whole body needs to be trained to lose fat all over.  Fat can be stubborn and people lose fat in the reverse order that they accumulated it.  Diet and caloric expenditure plays a significant role in fat loss. (American Council on Exercise Personal Trainer Manual, 4th ed, p360)

Myth #2

Women will get huge muscles from weight training

Most women do not possess enough testosterone (an anabolic growth hormone) to experience significant muscle hypertrophy (growth in size).  Even most men struggle to gain muscle mass.  Genetics plays a significant role in the body's ability to grow.  A specific and consistant training routine is required for the body to make any adaptation and gaining muscle mass is no different.  A training program that consists of 70% of 1RM (one-rep max) for three sets of 8-10 whole body exercises is not enough volume to develop excessive muscle hypertrophy in most women. (American Council on Exercise Personal Trainer Manual, 4th ed, p360)

Myth #3

People are too old / too young to lift weights

Resistance training is beneficial for all ages if done safely and appropriately.  Elderly individuals are still able to gain muscle mass.  Children too can engage in resistance training, though the focus of such a program should be on form and technique, not the amount of weight being pushed around.  Every age group can benefit from resistance training, such as increased bone density, improved body composition, and proficient motor-skill performance. (American Council on Exercise Personal Trainer Manual, 4th ed, p361)

Myth #4

Muscle turns to fat when a person stops exercising

Muscle and fat are seperate and unique tissues.  Muscle adapts to demands placed upon it, which is to say that muslces hypertrophy (grow) through resistance training and atrophy (shink) if the the training program is discontinued for a significant period of time.  Fat stores usually change with a training program as well, decreasing during training because the body is more active and burning more calories, then increasing when not training due to lower enegy expenditure.  Some simple steps to avoid this shift are to maintain an active lifestyle and balance caloric needs. (American Council on Exercise Personal Trainer Manual, 4th ed, p362)