it doesn't make sense that he can't get stronger by exercising because of his healing ability, it should be quite the opposite because he has super regeneration which actually makes him stronger quite fast, what the mc is talking about is restoration which would explain why he can't get stronger by exercising.
A thing that the author didn't mention before :
Why does Joshua have all Animal DNA in his own DNA ???
you didn't mention that jodhua assimilated such DNA before ....
Make Joshua go and learn various superhuman martial arts from Kun'Lun mountains & the members of The Hand ....
Those martial arts can make a normal human into a superhuman level .....
Using Chi , One can increase the strength & spedd of their body indefinitely , as long as they have enough chi ...
Also , Chi Manipulation can allow Joshua to learn self-Biology manipukation even better ...
He'll be able to comtrol his blood glow & other things ...
Lascivious