Average male adult gorillas tend to weigh around 300 to 400 pounds, and as they are growing, they climb trees to get to better food sources, and play by swinging on tree branches or jumping from one tree to another. When they are moving on the ground, they do not walk upright as humans do. They use their fists to move with their feet, like bears do. Because bears and gorillas are so heavy, and "walk" the same way, they are both have great upper body strength. However, due to the different pelvic sizes, bears tend to have stronger lower body strength because their pelvic structure supports most of their upper body weight.
In an evolutionary sense, humans had to adapt to different living conditions, whereas gorillas did not. Endurance was, and still is a factor for humans, while it is not for bears or gorillas. In the gorilla world, the usually the strongest gorilla becomes the leader, and gets to mate with all the females, much like lions and wolves, etc.
One of the most common myths about Gorillas is that they are several times stronger than humans. This is false. No strength tests have ever been done on gorillas. Some people say that gorillas are stronger than chimps and chimps are 4-6 times stronger than humans, therefore gorillas are much stronger than humans. This is also false, Chimpanzees are not 4 to 6 times stronger than humans. The study which lead people to believe that chimps possess superhuman strength was proven wrong in 1943 and again in the 1960s. There is a difference between pound for pound and absolute strength. A chimp's absolute pulling strength is equal to a human's absolute pulling strength.
However, the pushing strength of a human is probably much stronger than the pushing strength of any other primate due to our lifestyles. So, gorillas are probably stronger than humans at pulling but weaker than humans at pushing. Most gorillas weigh around 180kg while the heaviest can weigh up to 210kg.