10/05/2007 08:00 am ET Updated Nov 17, 2011

Personal Trainers: The Good, The Bad, And The Sometimes Ugly

A qualified and good personal trainer can help you build a great body, enhance your health and build self-confidence. But a bad trainer can cause more harm than good.

A good personal trainer will seek to enhance your strength, performance, endurance and flexibility, according to celebrity trainer Radu Teodorescu, also known as Radu, who has been in the field for more than two decades. "With personal training, someone makes sure you're doing the exercises right, realizing your full potential and making progress," he said.

Radu further adds "training can help some people change their behavior, develop character and build confidence."

But it doesn't come cheap. You're likely to shell out $75 to $300 dollars an hour, up to three times a week. Before you sign up, make sure the trainer is qualified. Poor training can result in permanent injury or make an existing orthopedic condition worse. "If your potential and individuality are not accurately analyzed, and if you are not taught in a scientific way, you can get hurt," said Radu. "Some trainers give the same program to everyone, and that can be dangerous."

Dr. Riley Williams, an orthopedic surgeon who specializes in sports medicine, issued another warning: "If you suffered an injury and need someone to help you with rehab, it should be a physical therapist, not a personal trainer, and you should be under a doctor's care."

"The problem is that some personal trainers are not taught to deal with medical injuries," he said. It's not uncommon for people to come to him after their trainer had them do multiple exercises or an activity that exacerbated an injury, said Williams, who is affiliated with the Hospital for Special Surgery in Manhattan.

Shoulders, knees and backs are most prone to injury from improper training regimens.

"If you're interested in personal training and have a problem or injury, first see a physician," advised Dr. Stephen O'Brien, a sports medicine specialist at the hospital and former assistant team physician for the New York Giants. "Make sure everyone is on the same team from the start."

It's a good thing a personal trainer called physical therapist Mickey Levinson to consult about a client. The 60-year-old female client had a rotator cuff shoulder injury, and the trainer wanted her to do bench presses. That type of exercise would have predisposed her to re-injury, said Levinson, a clinical supervisor at the Sports Medicine Center in the hospital's rehabilitation department.

"To find a qualified trainer, look for someone with background in physical education or coaching," Radu said. "The trainer should look at you as a whole person not in terms of inches. You should like the trainer and feel comfortable with him or her."

When embarking on a program, people who haven't exercised much should begin slowly, do things in moderation and know their body, sports medicine experts say. If an exercise or activity causes pain, stop immediately.

In choosing a trainer who is qualified and knowledgeable, you should ask your sports doctor for a recommendation. Personal trainers have much to offer to the public as they promote wellness, fitness, and overall healthy living. But it's not a good idea to choose a trainer based upon magazine features, the Yellow Pages, or other public relations items. Check with your sports medicine health care professional to avoid becoming a statistic.