I have doubts that it's realistic for a creature like Hulk to actually lift and throw cars and such heavy things without causing himself a torn muscle similar to what happens to a weight lifter sometimes. If not is there some explanation how Hulk's muscle tissue can withstand the stress from lifting and throwing very heavy things?
Even if he had the power to lift a car or the weight of a truck, wouldn't his muscles get torn or consist of some stronger tissue than what we know of?
If you are able to accept that he's able to resist and absorb the impact of a bullet, and even the impact of a tank cannon without a blink, you must admit that his body structure should be different from a normal human one. At least on a density/resistance level.
So... if his cells and tissue are strong enough to absorb high-velocity impacts without tear, why should they tear by high tension uplifting heavy weights?
With this question you are questioning the very nature of the character, but if you can accept his superhuman resistance you can accept that it also affects his capacity to resist muscular tension.
The Hulk has a number of powers in Marvel canon, though, as with most of their characters, those powers surround a common theme.
Growth. The Hulk is significantly larger than Bruce Banner, and has at times (depending primarily on which artist was writing his story at the time) grown larger the angrier he gets.
Strength. This is his most iconic ability, but without his other abilities, his body would rip itself apart using even a tiny fraction of his strength.
Toughness. His skin is substantially tougher than human skin, resisting bullets, blunt force trauma, and most other forms of damage. Should something manage to get through, it tends to make him even angrier, which has on a number of occasions caused attacks that wounded him early in an issue to be insufficient to damage him later.
Pain resistance. Frankly, pain just makes him angry, so even if he did dislocate a joint or rip a muscle, he most likely would give no sign of it.
Healing. While he is shown as being extremely resistant to damage, he also heals at a rate comparable to Wolverine. There are numerous fights between the two because they can actually go all out, ending usually either in a draw or in the Hulk throwing Wolverine a long ways away. Even in the live action series, David Banner*/the Hulk is shown healing from a broken back, though, admittedly, he did have to change into the Hulk twice before regaining his full range of motion.
There is no in depth explanation that I am aware of that actually compares the tissue of the Hulk to ordinary tissue. Then again, super strength is one of the most common** super powers, so people in that setting will be less inclined to study something that seems perfectly natural to them. When asking these sorts of questions, it is important to consider the POV of the characters who would be asking and answering them.
* He was named David Bruce Banner in the TV series because the producers were worried that the name "Bruce" sounded a little gay. Trivia Man strikes again!
** Third after universal attractiveness and gravity defying boobs, naturally.
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.
