Kumail Nanjiani walked into his workout regimen for "Eternals" as one big softy and emerged totally yolked thanks to high-intensity training, and a major focus on 2 key body parts.
Check out these workout videos of Kumail pumping iron with Grant Roberts ... the celeb trainer tells TMZ Kumail's transformation from scrawny to sculpted was all about intensity, and they trained for a little over an hour a day, 5 times a week for 10 months.
Kumail hit every body part training with Grant, but we're told the actor needed the most work on his shoulder and biceps, which were physically lacking when he started hitting the gym back in January -- Grant's words, not ours.