(CNN) -- John Moses plays tennis every week. He does push-ups and planks, shoulder presses and squats. He attends group fitness classes at an activity center three times a week, often taking two classes on Wednesdays and Fridays.
His strength, flexibility and six-pack abs have earned him a spot on the center's Wall of Youth and Fame. But the 75-year-old Atlanta man is just glad his joints don't hurt anymore.
"(Exercise) helps you capture the vim, vigor and vitality of your youth," he says. "You can do the things you did when you were younger."
Moses credits his energy to functional fitness, a type of exercise program that mimics the activities of daily life. For instance, lifting grocery bags out of the car requires forearm strength and balance. Putting those groceries away on high kitchen shelves could require shoulder flexibility and calf muscle stability.
"In real life you don't do an activity that singularly involves the bicep," explains Karyn Loughridge-Petty, program supervisor at the Center for Functional Fitness in Cuyahoga Falls, Ohio. "Functional fitness is focused on multi-joint activity. ... You rotate your body, put the strap over your shoulder, twist to put (the bag) in the car."
Functional fitness ranked eighth on the American College of Sports Medicine's list of the top 2013 fitness trends. Exercise programs for older adults ranked sixth.
The two are often one in the same, says Walt Thompson, professor of kinesiology at Georgia State University and lead author of the ACSM survey -- although functional fitness can apply to the younger generation as well.
Take, for example, a young man working on an assembly line in the automotive industry. He might not have the upper-body strength to manipulate large objects above his head. Or a restaurant server might need to increase her endurance so her feet don't hurt at the end of a long night.
"A personal trainer can imitate that kind of activity in the gym," Thompson says.
Smart commercial gyms are starting to offer senior functional fitness programs in the midmorning and early afternoon, Thompson says, when other exercisers are scarce.
"If they're not doing it, they're losing out on the potential revenue source that is huge. About the only demographic that has any discretionary money left is the elderly."
And it's a large demographic -- more than 41 million Americans were over the age of 65 in 2011. But as with any other age group in the United States, getting seniors to work out can be a challenge; in 2009, approximately 32% of older adults reported having no physical activity time in the last month, according to the Centers for Disease Control and Prevention.
A gymnastics coach and group fitness instructor for more than 35 years, Loughridge-Petty designed the Forever Young program for baby boomers in her area to provide a place for them to exercise at their own pace.
"I'm a physical person. I've always been a physical person," she says. "Do I want to be working out with 20- and 30-year-olds? Probably not."
As people age, there's wear and tear on the body. They lose muscle mass, bone strength and their sense of balance. Functional fitness focuses on keeping seniors independent as long as possible. Frequent exercise can help relieve arthritis pain, reduce the risk of falling and lower the risk of type 2 diabetes, according to the CDC.
The Forever Young program still has boot camp and Zumba classes, but they're different than the ones offered at the main building. The intensity and tempo aren't as high because seniors are more focused on building strength and flexibility. Another class has stations that mimic moves you would need to attend a theater performance: stair climbing; walking sideways down the aisle; sitting and standing up.
Basically, the end goal for functional fitness is different than your typical gym program, Loughridge-Petty says.
"What I want isn't a size 2," she says. "What I want is to be able to go to Hawaii and have a good time and not be worried about not being able to get my luggage in the overhead compartment. My leg muscles are strong not because I want to look great in a 4-inch heel, but because I want to be able to get in and out of a cab without help."