HOUSTON (KTRK) -- As a Body Pump instructor at the YMCA, Derrell Dunn is the picture of health, which is quite different from years ago.
He weighed 350 pounds, and the tendons in both his knees gave out from the strain of his weight when he stumbled in an accident, disabling him and forcing him to change.
We hit the treadmill with Dunn at a slow walk, which is all he could do at first.
"From doing this, I run 5Ks three or four times a year now," says Dunn.
PHOTOS: YMCA instructor on his life transformation
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He says you have to see the big picture in mind when you're tempted to quit.
"The memory of what I'd been through," said Dunn, "It's humbling to have to call someone at 2 am to put you on the toilet."
Dunn says coming to the Y provided a supportive environment that kept him accountable which is important to success, according to the YMCA's Jon Kidwell, "It can be a spouse that says let's meet at the Y, it can be friends that you meet at a group exercise class."
Finally, if you're going to invest your money in a gym membership, make sure you also invest the time.
New members at the Y can use a program called Smart Start.
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"We'll pair you up with a healthy living coach, and we'll walk through, so you get to know the facility, you get to know some people, and you get to know some of the benefits that are really useful."
Dunn says he first started going to the Y in his pajamas, because he had no formal workout clothes. It's been a long but rewarding journey so far.
"People will start exercising over a month or two, they may lose 5 pounds and gain 2 pounds, they may get depressed and want to give up, even if you gain a little weight back, keep going."
This Saturday, January 7, is 'Try the Y' day. All Houston area YMCAs are free to the community.
YMCA instructor loses weight and becomes an inspiration
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