It is corollary laws of physiology and physics that it is impossible to get muscles that big without becoming very, very strong. A simple fact of physiology determines that:
The individual contractile unit of muscle tissue, the sarcomere, does not become stronger. Which leads to a conclusion based on physics:
You can only become significantly stronger by increasing the number of sarcomeres in a muscle, and hence it's size.
I am using the word "significantly" because a lot of strength gains come from superior neuromuscular efficiency. But there are limits. Up to a point, the only way for a muscle to become stronger is for it to become bigger.
In other words, Coleman was just as strong as he claimed to be. He had to be to be 290 lbs with 5% bodyfat at 5'11. There is no other way.
SUCKMYMUSCLE