NEW YORK --Being in Ruth Hernandez's fitness class, you can't help but notice she's bursting with energy, quick on her feet, and has a passion for fitness.
One thing you not might not guess right away? Her age. Hernandez is 60, but seems to have the stamina of a 20 year old. She credits a lot of that to exercise.
"It just gives you so much energy. I can wake up in the morning and, bing, I bounce up," said Hernandez.
Beyond giving her energy and "tighter glutes," Hernandez said exercise helps keep her mind and memory sharper, too.
Medical science backs her up. "Unless you're living under a rock you know that exercise is good for you, but there are many things beside the obvious," said Dr. Jordan Metzl, a sports medicine physician at the Hospital for Special Surgery in New York.
"People think about exercise for their bodies, but for their brains it's probably more important. The science on regular exercise and brain health include ... less depression, better memory, better concentration, less risk of Alzheimer's disease. Brain health is dramatically affected by exercising four to five times a week," he said.
As people grow older, muscles, tissues and bone tend to deteriorate and strength diminishes, a process that accelerates after age 50 or 60. But regular exercise "can really slow that deterioration," Metzl said. "It makes a huge difference for how you age."
One factor doctors are learning more about is the influence of inflammation on a wide range of ailments.
"If you exercise more than four to five times a week you have much lower levels of circulating inflammation in your body. So pretty much every disease you can think of -- heart disease, diabetes, you name it -- is affected by chronic inflammation. And if you're exercising regularly that's lower," said Metzl.
"There is no drug that is as effective and really available to every single person as exercise. It works for everybody, young and old alike," he added.
Hernandez wanted to do whatever was within her control to avoid health problems as she aged. She decided around the time her mother passed away seven years ago that she was going to make fitness her lifestyle. Her mother had various health problems, some of which Hernandez said could have been helped by being active and staying fit.
"She passed on and I decided I didn't want to be like that. I want to be healthy, fit. Not doctors. Medical-free in every way," said Hernandez.
For the past year, Hernandez has been teaching a fitness class for a group of about 30 women three days a week in Queens, New York, through NYC Parks. She has worked with the department for 17 years coordinating after-school recreational activities for kids. But she had a real motivation to start helping people stay fit around her age. The women in the class are all over 50 and most are retired.
Some of the women told CBS News that if they weren't in Hernandez's class they would be bored, probably sitting home eating or watching TV. Many said coming to Hernandez's class has helped them feel stronger, both physically and mentally. They have less anxiety, more energy, and enjoy the sense of community.
Hernandez said the women have nicknamed themselves "The Divas." The women push each other to work harder -- and consider themselves like a family.
There is a lot of benefit to working out as a group, said Metzl: "Human beings are basically social animals and they will work harder and they'll be much more diligent with their exercise programs if they're in a group."
Beyond motivating each other, the women find inspiration in just watching Hernandez. The feisty fitness instructor shows no mercy as she demonstrates moves and exercises with the group. They squat, lift weights, and work muscles Hernandez said they wouldn't normally work.
It sure doesn't look a "senior fitness class," and Hernandez makes it that way on purpose. She said she wants to be an example "and let them know, 'listen, if I can do this you can do it, too.'"
Her tough-love approach has helped bring about changes she has personally seen in the group. She has seen the women become happier, have less back and joint pain, and grow more confident.
At the end of class Hernandez and her students dance it out, some with weights still in hand. Hernandez busts out a few dance moves herself, and steals a few proud glances at the group around her in the gym.
"It's amazing what your body can do for you, no matter what age you are," said Hernandez.
"Fitness has no age, there's no limit. Fitness is for life. ... and I'm proof."