When Peter Parker transforms into the Amazing Spider-Man, he instantly develops incredible powers. He shoots spider webs from his wrist, sticking the ropy ends to skyscrapers as he swings through the metropolis battling evil and saving the day.
Let's start with Spider-Man's origins. He didn't create his superpowers in a secret lab. Instead, a radioactive spider chomped on him, permanently altering his DNA and making him an athletic freak of nature.
Then there are those long strands of webs that seemingly emerge from his wrists. Those dozens of feet of web have to come from somewhere, because matter doesn't just spontaneously materialize. Even if those webs were fashioned from his own body's cells, he'd run out of mass after just a few long swings. That's particularly true of the fantastically strong web material, which has a tensile strength of about 120 pounds per square millimeter.
Then there's all that swinging and jumping. As Spider-Man hurdles off of tall buildings and into a downward swinging arc, his body remains remarkably intact, with nary a shredded limb or broken neck. That's in spite of the incredible acceleration and deceleration he'd have to withstand. Those forces are entirely too much for a normal human body, and possibly too much even for a superhero like Spider-Man.