The drama series, which hails from Applause Entertainment, is based on the first chapter from Shiv Aroor and Rahul Singh's book "India's Most Fearless".
"When I got to know about this role it got me extremely energised and I wanted to put my best self forward, so I decided to undergo the physical transformation," Sadh said in a statement.
"It was a conscious decision trying to show the physicality and the strength the Special Forces have. I was 72 kg when I was offered this role and now I am 90," he added.
The actor underwent physical training and followed a strict diet to gain weight. He trained with Rakesh Udiyar, the trainer behind Aamir Khan's look in "Dangal" and Salman Khan in "Sultan".
The show is expected to stream early next year.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)