Jor-El explicitly links strength and senses to radiation, but because he mentions weaker gravity and Earth’s nourishing atmosphere [FN1], there is the misconception that Superman is powered by weaker gravity or Earth’s atmosphere. This is clearly not the case.
Superman’s powers are not dependent on gravity. Superman’s exhibits his powers under the weaker gravity of space and under the stronger gravity of the World Engine’s beam. Superman’s powers are not dependent on Earth’s atmosphere. He exhibits powers in a noxious oil rig fire with atmospherics low on oxygen. His powers allow him to survive an entire dream sequence underwater in the frigid ocean. He demonstrates, flight, strength, and durability in his multiple trips to the vacuum of space. Superman is not holding his breath. His mouth is open before he rescues Lois from the damaged escape pod. He and Zod vocalize during the satellite fight and on their return back to Earth. Even Jax-Ur explicitly ties Kal-El’s strength to radiation.
So why the confusion?
Partly because of a misunderstanding about Kryptonian helmets. Faora calls part relevant to Lois’s respiration a breather, but that doesn’t mean the helmet’s sole function is to serve as a breather (or that a helmet is called a breather). For example, if I handed you a cellphone and said, “Hold the microphone to your mouth to be heard.” I’m speaking about the part of the cellphone relevant to you being heard. It doesn’t mean the only function of a cellphone is to act as a microphone or that a cellphone is called a microphone.
This is supported by Superman’s explanation of Zod’s sensory overload. Superman has just learned that the apparatus contains a breather. If Superman believed the sensory overload was caused by or related to atmospherics, he would have said “breather.” Instead, Superman says, “helmet” because the source of the overload isn’t breathing Earth’s atmosphere but the fact that their helmets are no longer sealed from all non-filtered sound.
Just as their helmets have the capability to filter light into safe and comfortable ranges, and just as human military has the technology today, Kryptonian helmets bring the din of war down to safe and comfortable ranges until they’re damaged or compromised.
What does affect Kryptonian powers? The presence of Kryptonian atmospherics. Superman’s strength returns not because he’s breathing Earth atmospherics but because the Kryptonian atmospherics are displaced. If Superman was powered by Earth atmosphere, his strength would quickly leave him, exposed to the vacuum of space when Jor-El tells him to strike that panel.
Again, it isn’t gravity. Superman is perfectly fine flying around the World Engine, until he breaths some unknown concentration of Kryptonian-like particulate / atmosphere, which causes a brief coughing fit. When he leaves the cloud, his powers immediately return.
Of course, if Kryptonian atmosphere affects their powers, how was Zod able to demonstrate powers on Smallville? Watch the other videos in the series to find out!
[FN1] Why does Jor-El mention gravity and atmosphere at all? Essentially to explain how Krypton is a harsher environment and why Kal-El can survive is Earth’s environment but humanity cannot survive in Krypton’s.
If you’ve got an idea for a myth that my meager editing abilities might be able to tackle let me know for future videos!
Man Of Steel Answers Insight Commentary (MOSAIC) Podcast covers these kinds of questions and more in depth for fans of Man of Steel and those excited by the DC Cinematic Universe.