Melissa McCarthy 75-Lbs Weight Loss & Fitness Secret: Everything you Need to Know About Interval Training

The "Identity Thief" star Melissa McCarthy has lost as much as 75 pounds lately according to reports. But, one source said that McCarthy's dramatic transformation was not intentional at the onset.

She had to be fit for her role as Susan Cooper, a CIA agent, in Paul Feig's 2015 film "Spy." And, while it all started as a chance event, McCarthy was able to maintain the slimmer figure on her way to reaching the thinnest she has ever been.

"Melissa never expected to drop all this weight. She has no intention of losing anymore, but if by following the same plan, it drops off, she's not going to complain," a source told OK! Magazine, the InTouch Weekly noted.

According to celebrity trainer and nutritionist Charlene Ciardiell, the success in weight loss and fitness of the 45-year-old American actress and comedian can be attributed to interval training, apart from a healthy diet.

"Hit the pavement or treadmill for 20 to 30 minutes, alternating between walking or jogging for a minute, then running or sprinting for a minute," she said.

Interval training is a type of workout where you try to alternate short but high-intensity bursts of speed with slower, recovery periods, according to Shape.com. It could be a minute of sprinting in full burst followed by another minute of walking to catch breath and recover a bit. Then, repeating the process over for a few sets.

Interval training is perfect for those who do not have much time to workout as optimal results are achieved in doing the workout for short periods of time. One of the popular types of interval training is HIIT or High-Intensity Interval Training. Some of the benefits from incorporating HIIT to your fitness routines include a boost in the metabolism, building lean muscle, and keeping the body burning calories up to 48 hours after the workout, says Greatist.

The interval training may not be tailored for everyone, though. The Mayo Clinic advises consulting a doctor first for those who would want to try it out but is suffering from a health condition, or those who have not been in the best of shape lately. Those who have not been doing any fitness routines must be careful of pushing themselves too much with the interval training. In doing so, they might be risking injuries on their muscles, tendons or bones.

On the other hand, the Mayo Clinic added that there are studies showing that interval training can be used safely for short periods even for those suffering from heart disease.