"Biggest Loser" trainer and Shape Magazine consulting fitness director Jen Widerstrom answers viewers fitness questions with The Doctors.

One of the viewers asked via social media what is the best way to sculpt muscles? Is it through HIIT – High Intensity Interval Training – or is using weights the best way to gain muscles?

Watch: Drs. Rx: Drink THIS to Hydrate and Soothe Sore Muscles after a Workout

Jen says, “You don’t have to pick one.” HIIT is working very hard for a short amount of time followed by a break. Jen says you can include weights within HIIT. ER physician Dr. Travis Stork asks what to do if you’re not into super hard-core HIIT.

Jen explains you can break up the sessions depending on how you feel that day. You can do a 15-second on/45 second off work-to-rest ratio. If you’re feeling stronger one day, you can do 45 seconds of hard work followed by 15 seconds of rest. Jen’s advice, “Don’t judge yourself. Just give what you got that day.”

Another social media question on The Doctors' Instagram @thedoctorstv for Jen, “What can you do if you’re stuck at a weight no matter how much exercise you’re doing?”

While changing it up and keeping the body guessing is helpful, Jen says that 9 times out of 10 the reason for a plateau is that people aren’t adequately nourishing themselves. Jen talks about how once people drop weight they need to reassess the numbers they are hoping for on the scale.

Dermatologist Dr. Sonia Batra points out that muscle weighs more than fat. It may seem surprising, but Dr. Travis says that eating an extra 100 calories of good food may actually help your body push past that plateau.

But what if you still have that stubborn belly pouch? While you can’t spot train, there are ways to tighten it up. Check out these two ab-strengthening moves and learn the proper way to breathe while doing them. Also, find out what plastic surgeon Dr. Andrew Ordon says to crack the other Doctors up!