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By Danielle Leigh
(NBC News) Virtual coaching is becoming big business, exponentially expanding personal trainers' client base and promising anyone who signs up fitness on their own schedule.
Ivan Black is a certified personal trainer, but he doesn't meet many of his clients at the gym. He coaches them from his family room, online and by phone.
He's among the growing number of trainers turning to the internet for new clients who want to be in shape, but for whatever reason may not sign up for a gym membership or personal training.
"I got up to a point where I ran out of time and there was a need to reach more people," he says.
People like Theresa Firestine, who now get daily customized work outs from Ivan for a fraction of the cost of personal training.
"Its a lot better for me because if I were to go to a gym I would have to go at a specific time for the class and the class may not be targeted to my level or my needs," Firestine says.
Virtual coaching has become so popular Well Beats, a leading provider of fitness classes on request, and Anytime Fitness, a gym specializing in digital training, have both been named top growing companies.
Still, sports scientists caution there is a down side.
"There is a chance for injury, and if you are doing that without supervision there is an increased risk for injury," warns Rich Richey of the National Academy of Sports Medicine.
Anyone interested in personal training should be clear with the trainer about their level of fitness and personal goals and never do a workout they aren't comfortable with, and reach out immediately about any unusual soreness.