A thought experiment: If you ease the bumper of a car against a concrete wall, and then press the gas pedal all the way down, the engine will expend a lot of energy but perform no useful work. The chemical energy in the fuel is burned, but all of the effort is wasted, converted into heat and noise.

What you describe is the same. Your muscles burn chemical energy (fat, sugar, etc.) whenever they try to contract. At the microscopic level, they are moving quite vigorously. Whether or not that results in any macroscopic motion (i.e., kinetic or potential energy) depends on the situation. Straining to lift an object that is too heavy is not an efficient use of what those muscles could do, just like the car pushing against an immovable wall.