Zenkai (全開; lit. "Full Release") is an integrated mind-body technique developed by Ranma when he first learned to use chi and ki as weapons on Jurai that allows the user to constantly expand their reserves of ki.
This technique altered the flow of ones ki so that it continuously cycles throughout their entire body allowing their reserves to continue to grow, but not to the rate where they would trash user’s body i.e. a workout without doing the work. However the technique wasn’t perfected upon it’s creation as Ranma didn’t take into account that a practice of both mind and body means simultaneously cultivating the mind and tempering the body. This flaw causes the user’s reserves to grow far quicker then anticipated making impossible for user to restore their ki flow to proper order.
This causes the body to have more energy than it is trained to hold and use adequately. If the body is not trained to a high degree, then even if the mind were capable, the body would falter. It would be impossible for user to keep up with their reserves and everyday, the gulf between the two will grow larger and larger until the strain eventually kills them. In the end Ranma perfected this technique eliminating this weakness.