(CNN) Personal trainer Mark Fleming flashes an encouraging smile as he pushes a young man through the paces. It's a simple exercise, stepping over a hurdle. But for his client, there's nothing easy about it. Fleming understands. He knows a lot about life's hurdles. And like his client, he is on the autism spectrum.

"I think it is important to help others on the spectrum to achieve the life that they desire. And exercise is a great way to do that," Fleming tells CNN. "I have them do this exercise to get the brain working... Coming to a new place can be challenging to an individual with autism."

Spotting a disturbing trend

Fleming graduated from the University of Alabama with bachelor's and master's degrees in exercise science. While working as a Special Olympics volunteer, he learned of a disturbing fitness problem for many of the participants.

"There was nothing for people with autism to stay active [after the Special Olympics ended]. And they would end up regressing. A lot of the time, people with disabilities stay at home a lot and become sedentary."

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