How Halle Bailey built an 'insane' core and toned her shoulders for 'The Little Mermaid,' according to her trainer

• To play Ariel in "The Little Mermaid," Halle Bailey had to get as strong as possible.
• She needed a strong core to film scenes with a rig around her waist, her trainer told Insider.

Halle Bailey was in the best shape of her life when she filmed "The Little Mermaid," she said.

The actor, who plays Ariel in the live-action remake of the Disney classic, had to be. She spent hours filming in front of a green screen while attached to a rig that suspended her in the air from her waist, all so she'd look like a mermaid gliding through the sea in the movie.

Sana Shirvani, the London-based strength and conditioning coach and personal trainer who worked with the movie's star-studded cast, told Insider in an exclusive interview that core exercises were incredibly important for Bailey and the rest of the mermaids, and they worked on sculpting defined shoulders too.

"Aesthetically what the producers wanted was of course a nice looking core, but also shoulders and arms were quite important, so just having a little bit of definition through the shoulders and rear delts was also quite important," Shirvani said.

Just because you have a tail doesn't mean you get to skip leg day, though.

The cast maintained their strength and physiques for nearly two years

Shirvani worked with the film's leads, Bailey and Jonah Hauer-King, who played Prince Eric, for three months before filming was due to commence in March 2020. But the movie was put on hold just three days before production was set to start when much of the world went into lockdown at the start of the coronavirus pandemic.

What was meant to be a nine month project ended up spanning two years for Shirvani, who is soon to launch a one-on-one training app and also trains clients at Until, a series of "wellness optimization facilities" across London.

Bailey and Hauer-King were in perfect condition for their roles, and they then ended up having to maintain their strength and physiques for eight months before they could actually start filming.

Bailey went back to LA from the UK and Shirvani trained her and gave her nutrition guidance virtually while they couldn't be together.

Bailey needed 'insane' core strength to play Ariel

Bailey was in great shape from the start, Shirvani said, so the main aim was to build her strength for such a rigorous role.

In pre-production, Bailey trained with Shirvani for 60 to 90 minutes, five to six times a week. Once filming started, this decreased to about three times a week, as and when workouts could be fitted in. Shirvani made sure not to push the actors too hard, because filming was taking such a toll on their bodies already.

The mermaids and Hauer-King also all did swim training outside of the gym to build their strength for filming storm scenes in a huge water tank at Pinewood Studios in the UK, as well as scenes in the sea in Sardiniam Italy, Shirvani said.

However, the majority of the mermaids' filming was done on a rig that was essentially wires clipped to a harness around their hips.

"You're supported on the hips and you move into horizontal, vertical, and diagonal positions, and you've only got support around your hips," Shirvani said. "You've got to have an insane amount of core strength, an insane amount of back extensor strength, as well as strong hips, glutes, and hamstrings to be able to support your lower body."

For this reason, Bailey's workouts were full-body. Deadlifts and hip-thrusts were staple exercises for the lower body, Shirvani said, and they employed progressive overload — gradually increasing the weights or reps — in all exercises.

To help the mermaids build their deep abdominal core muscles, Shirvani started with basic bodyweight exercises like deadbugs, planks, side planks, and other isometric holds (where the body is still in one position).

"It was more about getting them to understand the mind and muscle connection with their deep abdominal muscles rather than thinking that their strength comes from having a visible set of abs," Shirvani said.

They then progressed these exercises by adding resistance with bands and cables. Once they were comfortable with those, they started doing exercises using a GHD machine — which stands for Glute Ham Developer but is also an effective way to train the core.

"The GHD was a lifesaver for me because that pretty much mimicked the harness that they were on," Shirvani said.

They used the GHD machine to perform isometric holds such as face down planks, which strengthens the back muscles, as well as hollow holds facing upwards, and side planks.

Bailey also performed anti-rotation and spine flexion and extension exercises on the GHD because she had to do these movements on the rig too, Shirvani said.

The mermaids even had to train their necks

For the mermaids in the film, strengthening the neck muscles was especially important.

"Being on the rigs and being horizontal, they've got to be able to swim like a mermaid, move like a mermaid, and also be able to sing, act, and dance pretty much with a straight face without being in pain," Shirvani said.

Once again, the GHD came into play.

"We put them on the GHD with a neck brace which had a chain on it, and we would put 1.5 to 2.25 kilograms (3.3 to 5 pounds) on that chain and they would just isometrically hold for anything between 30 to 90 seconds," Shirvani said.

Bailey, who's vegan, ate whole foods and plenty of protein

When it came to nutrition, Bailey had the goal of maintaining her body composition, rather than fat loss.

She is a vegan and Shirvani's main guidance was to focus on whole foods and eat plenty of protein to help build her strength and enable her muscles to recover from training.

"She is in great shape, she has a phenomenal figure as it is," Shirvani said, so she wasn't worried about Bailey getting "out of shape" during the coronavirus lockdown.

When the cast and crew went to Sardinia to film the scenes that weren't in a studio, Shirvani encouraged everyone to relax their diets and enjoy themselves.

"In terms of nutrition, they were able to pretty much have what they wanted then," Shirvani said. "But that was right at the end of the production. I knew that there wasn't anything that was going to hinder their results."