I'll stipulate to running and standing in gravity (but not in full gravity as I'll explain presently). That pic clearly shows them designed to lope along like a very angry mountain cat (minus a leg of course).
However, Dark 4ce, you forget that squids and the like don't ever real mass with those tentacles. You don't push loads with rope. You pull them, because you have no rigidity with which to push them. Bones and exoskeletons provide that.
Whilst an exoskeletal beast like an ant can indeed push up and carry a ridiculous multiple of its own mass, this has something to do with the size of the creature to begin with. Take a look at crabs sometime. You'll notice that hard shelled crabs don't get very large, and those that do are ponderous and slow. Shivans are not ponderous and slow. If you further examine arthropoda, you'll find very large creatures, like South American bird-eating spiders. Those can be as much as a foot long, but they lack an exoskeleton. They couldn't catch birds if they had one because their own exoskeleton would slow them down--or even render them immobile.
When dealing with the motive capacity of animals (humans and Shivans included) you deal with something called the square-cube rule. As the linear size of a volume increases, the rate of surface increase is the square of the linear increase, and the volume is the cube of that linear increase.
Imagine a 1m square. If you double its size to 2m*2m, the surface area doesn't go up linearly. The progression is a square function. When you start dealing with volume, it gets even uglier, as the progression is a cubic. when you double the dimensions of a 1m cube to 2m, you end up with eight times the volume, and consequently eight times the mass (2^3=8). Imagine the increase in mass required to bring your ant up to the size of a Shivan. Now imagine the how much more muscle tissue would be required to move that mass. At a certain point, no matter how much muscle you add, its own mass outstrips its own ability to move itself. Thats why there aren't any human sized exoskeletal beasts on the surface of the earth.
Venom pointed out the possibility of cybernetic enhancement as possible explanation, but I don't buy this theory. I agree, indeed, that Shivans probably tote around cybernetic enhancements in their bodies, but servo-motors for asissted movement? I think not. Imagine a growing shivan. He would have to have his servos replaced year after year. As there is no external evidence of these motors, they must be internal, and thus a shivan undergoes surgery regularly to upgrade his internal motive systems. Further, a Shivan whos cybernetic enhancements fail is stuck, unable to move under his own weight until his buddy, Carl the Shivan (not to name names) comes along and helps him to a doctor/mechanic.
All of that can be avoided, however, if you look to the example of ocean going arthropoda, such as giant sea crabs. When I lived in West Germany (for such was it called back in my day), we went to a natural science museum and saw a crab with legs longer than my entire body! How could such a beast support itself? Water is buoyant and sea water especially so. The water helps the sea crab support itself by lowering its effective weight. A shivan, adapted to low gravity, would not need water or servo-motor implants to move because he would not weigh as much. He would still have to overcome his own mass and inertia, but that's a different thing entirely.
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"Your guy was a little SQUARE! You had to use your IMAGINATION! There were no multiple levels or screens. There was just one screen forever and you could never win the game. It just kept getting harder and faster until you died. JUST LIKE LIFE." --Ernie Cline