Three Options

With his whole body from head to toe being restricted, glued to the bottom of the sunken ground, even with his muscular body and literal inhumane strength that he possess, the muscular humanoid demon wasn't able to tap into his strength to get his body out of the current predicament he was currently in.

Not even able to move his muscles except for doing small twitches of his minor muscles, even the muscular humanoid demon wasn't able to generate enough strength to destroy the darkness tendril that latched onto his body.

If the number of darkness tendrils were in the ordinary amount or to be more particular, in the number of one darkness binding spell could manifest, then the muscular humanoid demon would have enough strength to break through the darkness tendrils that would be considered poor in quality of toughness in comparison with the muscular humanoid demon's strength.