I want to thank you for correcting my mistakes. I well knew that Italian word FORZA is strength, but after writing once in wrong way, I continued without thinking. Sorry, don't hesitate to correct my English when I write something wrong, is a good way for learning something better. Thank you again, next time you can also write your name, because you have reason.
Regarding the question about the TECHNICAL WAY for running hills, I can say, from my experience, that :
a) If you have an athlete running with very short strides, using high frequency, he needs to increase his strength and must use sprints climbing more for muscles than for nervous system. In this case, he has to push using long strides, also if the speed is a little bit slower than running with more frequency.
b) If instead you have an athlete using long strides (and of course slow motions), is better that sprinting he uses the idea of "skipping", running with very high knees and trying to increase his frequency. For him, RAPIDITY is more important than strength.
At least, short hills have the goal of improving the DEFICIENCIES rather than improving the qualities that you already have. Using hills, and mixing length, gradient and technique of running, you can leave a mark on different qualities, from nervous reactivity to the capacity in recruiting fibres, training all what you need for having and using more strength.