Just training to approach your physical limits may make you better, but only to a certain extent. You've got to pick those days where you exceed those limits and go to your very breaking point, you've got to train to your mental limits. Try picking one day a month to push yourself right over the edge, not just before the edge, but right over the thing. Next time you go to train, your mental AND physical limits will be that much higher.
You see, training just before your breaking point will mean you always will have the same limits. Training just past the breaking point, until compete physical AND mental exhaustion means you have just broken through that wall and set a new standard, a new limit. Its not always about how much of a physical exercise you can do, sometimes its about how many times you can get into the position and fail. The effort you make to achieve the movement, not just the movement itself.
"I have trained my mind, and my body will follow"