But one Chicago area trainer has figured out how to do that despite her progressive vision loss.
Once a commercial interior designer, Joan Creviston changed careers, to something she is not only passionate about but can still be challenged by.
Nine months ago, Lisa Starks started training with Creviston.
"I called the fitness center and I said I want a female and I want somebody older and I want someone who will listen to me and they said Oh you need to talk to Joan," Starks said. "I had worked out with her for a month and had no idea that she has a vision issue."
Joan was born with vision loss.
"It's a heredity condition called retinitis pigmentosa, Creviston said. "I was diagnosed when I was in my early twenties. Since my 20s, my vision has gotten most worse. It's progressed quite rapidly.
"I have enough vision right now to see what they're doing. I really understand the kinesiology of how the body moves and I can tell if it's moving the right way and I can tell when it's not moving the right way."
Since Starks began working out with Creviston, she lost a total of 70 pounds. She is 10 pounds away from her goal.
Beth Goncher is another client of Creviston's who didn't know she has a vision loss for several months
"She was constantly looking at form and you know making sure you filled the lines, making sure that the reps that we were doing, the form was correct and she was very specific about that," Goncher said.
Creviston, who is also involved with the foundation Fighting Blindness, developed a training DVD called "Visual fitness training with Joan Creviston."
"It's five- to 10-minute exercise modules of what's considered metabolic conditioning, so it's a real high intensity for a short period of time," she said.
"I'm going to continue training and personal training and group exercise instructing for as long as I visually can and I'm going to continue to grow visual business, my virtual business, my internet business to include as much as can," she said. "I would love to get into podcasting. I would love to expand my library of exercise modules. You know when it comes to that, I have a lot of great ideas and my future looks bright."