One can break this rule sometimes and try to put his energy into ...
I am especially concerned about the usage of 'his' along with 'one'.
I wanted to use one's instead of his but that gave me a sense of wrong sentence formulation because of multiple uses of 'one' in the same sentence.
There is nothing wrong with using one and one's, but it doesn't read that well. If you want to keep one at the beginning of the sentence, then you can use their in place of his. You will get a mixed reception about whether or not this is grammatical. (https://en.oxforddictionaries.com/usage/he-or-she-versus-they)
If you're opposed to that, another option would be to pluralize both one and his, so that it reads,
People can break this rule sometimes and try to put their energy into...
If you could come up with something more descriptive for one, you could also go with,
An athlete/Athletes can break this rule sometimes and try to put their energy into...
