By Editor 
The strongest muscle based on its weight is the masseter, the primary chewing muscle. With all muscles of the jaw working together it can close the teeth with a force as great as 55 pounds (25 kilograms) on the incisors or 200 pounds (90.7 kilograms) on the molars.
Our money was on the gluteus maximus (buttocks).
Image source: Spotty11222 at English Wikipedia, Public domain, via Wikimedia Commons
K J Foxhall