The Hulk doesn't tear his muscles, not because of muscle density or toughness or regeneration, but because he's not actually using his muscles the way he seems to be.
The Hulk weighs, canonically, a maximum of approximately 1450lbs. However, the Hulk can generate, also canonically, a force upwards of a million pounds per square inch with his fists or feet.
This means that if he was using his fists to strike the ground, which he loves doing, he'd fly off the planet each time, because there is no amount of leverage that can hold him down.
The Hulk has other "secret" abilities. He generates an immense kinetic force that he uses to deliver his blows (which is why he never bleeds or breaks a knuckle no matter what he hits... because he's not actually hitting it) and to protect himself from bullets and tank shells (which is why he has, in more recent years, become completely wound proof, and not just taking the shots and moving on).
That is why he doesn't tear his muscles. He can't. He'd have to use up his energy source before even getting close to doing so. And then it would heal in seconds.