Denise Austin knows health and fitness like the back of her hand. 

After more than four decades in the industry, she's seen every fitness fad come and go and knows there are only a few ways to truly stick to a healthy routine for life.

"Just do something that makes you feel good," Austin exclusively shared with Fox News Digital. "I love to walk for fitness. I love to do light weights to get strong and stay strong. I like to stretch and do yoga. Mixing it up is really fabulous. That way you're surprising different muscle groups, and you kind of keep everything going and not plateau.

"I really think anybody that enjoys what they're doing — maybe it's pickleball, tennis, any form of fitness — just move. Move as often as you can. Standing up burns more calories than sitting down."

DENISE AUSTIN, 66, SAYS SHE'S BEEN DOING 30-MINUTE WORKOUTS FOR 40 YEARS: ‘IF YOU REST, YOU’LL RUST'

Austin, who has sold more than 24 million exercise videos and DVDs throughout her career, authored a dozen books and starred in a fitness television show, said there's one simple trick anyone could do to stay fit and lose weight.

"My favorite tip, I tell everybody, is good posture. Posture tells a lot about somebody," Austin said. "If you're slouched over, first of all, your tummy has nowhere else to go but out. But if you sit up nice and tall, put your shoulders down and back and zip up those abs.

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"Keeping your spine healthy is so important. And then when you're standing up nice and tall, you can kind of tighten up your tummy for five seconds. That's equal to one situp. So, you could be doing these isometric exercises throughout the day that really work your muscles."

The fitness guru starts each morning with a 30-minute workout, which she believes helps her not only jump-start her day, but set the tone for any mental hurdles she may have to face.

"It actually carries me throughout the day because I feel good, like I accomplished something. It's that wonderful feeling of self-accomplishment," she said. "So, that's why I want someone to say, 'You know what? I did 10 minutes today. Hey, that's fantastic. Start small. If you haven't worked out in years, start with just a ten-minute walk around the block and then build up to that. You'll get fit that way."

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Taking the mental pressure away by working out in the morning gave her small goals to look forward to during the day. 

"When I exercise in the morning. I don't have to worry about it during the day," Austin said. "That way, I feel accomplished. And, also, at dinner time, I want to make dinner and have my glass of wine."

As for the trend of Ozempic usage for weight loss, Austin admitted that using short-term weight loss solutions could go "both ways" in her industry.

"I always tell women, ‘Just stay fit. Do things that are going to work your muscles.’ See, muscles are very important," she said. "They work miracles on your metabolism. So, also, to strengthen your muscles, to fight osteoporosis and stay young, nothing will droop or sag if it's nice and toned and taut. So, no matter what you're doing, make sure you're still doing some muscle conditioning exercises. They are key to keeping us young and vital.

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"You still want to do some cardio to work on the heart. The heart is a muscle just like your biceps. So, you need to do something cardio to work the heart. And then you want to do some strength training to tone your muscles and then some flexibility, too. Stretching. All three are important for kind of like an overall wellness program: stretching, toning and a little cardio, like walking."

Austin recently flashed her abs alongside daughter Katie, 30, for the cover of "Women's Health." Katie, a former lacrosse player, found a passion for fitness and is paving her own way in the industry.

"It's a dream come true that my daughter Katie is following in my fitness footsteps, and she's so great," Austin said. "She teaches me things now, so it's fantastic, and it keeps me up."

WATCH: FITNESS ICON DENISE AUSTIN SHARES ENTHUSIASM OVER DAUGHTER'S PASSION FOR HER OWN FITNESS CAREER

The "Fit Over 50" founder credited Katie with helping her navigate social media and teaching her innovative ways to market her work with technology, no easy feat for someone who began teaching fitness on the "Jack LaLanne Show" decades ago.

"Now I'm dedicated to women who are wanting to be fit over 50 because I'm 66 now, and I want people feeling good," Austin said. "Wake up happy, feel strong. We need to work out our 640 muscles from head to toe to get strong and feel good."