FORT JACKSON, S.C. -- The South Carolina sun -- causing blistering temperatures to climb throughout the day -- didn't slow down Sgt. 1st Class Elizabeth Calderon from her workout.

For her, being a Master Fitness Training instructor means that flipping tires or carrying ammo boxes in the heat is another day at the office.

The former drill sergeant, no stranger to Fort Jackson's long summers, was wearing a weighted tactical rucksack on her back, Sept. 24, as she demonstrated modified squats outside of the U.S. Army Physical Fitness School.

The purpose of her workout was to show proper ways Soldiers can better prepare for the Army Combat Fitness Test -- even with limited resources. Calderon was increasingly fatigued as the day wore on, yet pushed through and never compromised her form.

"She's the heart of the program," one of her colleagues was overheard saying as she continued demonstrating exercises.

Calderon, a former competitive bodybuilder and fitness guru herself, finished the squat the right way -- the Army way -- then wiped sweat from her brow, and replied with a smile.

During her time as a drill sergeant, Calderon said she spent countless hours in the gym, and rep-by-rep, sculpted her physique. For her, bodybuilding was an outlet to the highs and lows she faced while "on the trail", she said.

"When you can physically move and train your body to accomplish things you never thought you could before," she said, "You find yourself."

These days, however, although strength conditioning is still essential, she relies on functional workouts.

These workouts, taught at the school, are well-rounded and cardio-intensive, designed to help Soldiers balance strength with endurance. After all, big muscles don't necessarily mean physical fitness, at least according to Army standards.

For the last 10 months, she's been an instructor at the school, where she, along with the other instructors, educate and certify selected Soldiers, from units around the Army, with everything related to the Army's Physical Readiness Training program, including how to properly grade the ACFT.

Although the instructors' job requirements stretch far beyond the ACFT -- from helping Soldiers develop physical training concepts, tactics, techniques, training programs, and other aspects related to the PRT -- lately, all eyes seem to focus on the upcoming fitness test, she said, which is heading into its second phase of implementation beginning Oct. 1.

During the second phase, all Soldiers will take the ACFT as a diagnostic and all Initial Military Training officers and enlisted will take the six-event fitness test as a graduation requirement.

The fitness classes aren't just taught outside or in the gym, though. Many courses are also taught in traditional classrooms. There, instructors discuss topics such as injury prevention and nutrition, among many others.

"It all goes hand in hand," Calderon said, referring to Holistic Health and Fitness, or H2F. "If your mind isn't in it, your heart isn't either -- if that's the case, you might just not have the motivation and do what you got to do in the gym."

"I think you need to be 'centered' in order to perform well," she added, saying all aspects of H2F health are vital to success.

Some Soldiers, according to Calderon, are still uneasy with the ACFT's test requirements, including events such as the leg-tuck. That's where, according to her, practice makes perfect.

"I think people fear what they don't know," she said, regarding the new fitness test. "Once they're out there doing the movements, they'll realize they can do it, too. I'm here to teach Soldiers how to design a [fitness program] they can bring back to their unit."

Program design skills Soldiers learn at the school "will carry over into training for the ACFT," she said, and when certified Soldiers return to their units, not only are they qualified to grade the ACFT, but they can supervise it, and set up the field for testing.

"People may not realize it, but many of the ACFT exercises target muscles they work out every day," she said. "My job is to help teach Soldiers the techniques used to perform those exercises correctly, and with proper form so they don't get injured. Soldiers have been moving this way all their lives, they just need to perfect the movements and build a foundation."

Whether it's in the office, or at the grocery store, "our muscles are designed for functionality," she said.

"We do dead-lifts when we pick up our groceries," she said. "Or, bringing them to their car is like the farmer's carry."

By utilizing a certified MFT, Soldiers will be one step closer to optimal physical readiness. However, according to Calderon, they still need to believe in themselves.

"If a Soldier is in the mindset they won't pass the ACFT, they won't," she said. "It's just like if you start your day believing you'll have a bad one -- then you will."

In addition to her students, who occasionally reach out from time to time, Calderon has also developed an army of followers on social media, too.

With more than 16,000 followers on Instagram, Calderon -- known online as fatgurlliz -- uses her social media presence to empower others, by promoting physical fitness and body positivity.

Although it's her private account, she said she receives many messages about Army fitness.

"My advice is if you have fun with (the ACFT), then you're going to perform well -- but you have to train the right way," she said. "Train properly, and once you develop the endurance that you need, you're going to be okay."