It's all a question of idiom.
"Is helpful to doing something" is not good idiom. "Helpful in doing something" is a little better; better yet is "helpful for"; but best of all, why not just say "helps"?
X "This is helpful to running." Poor.
V "This is helpful to him" (a person doing something, not the abstract action). Good.
-- "This is helpful in running". Passable, but a little odd.
V "This is helpful for running". Acceptable.
V "This helps him". Good English!
V "This helps him run". Good!
V "This helps his running". Good!
X "This helps running". Not so great.
V "This helps in running."
V "This helps to run". Good!
I'm not going to attempt an explanation of why some of these phrases sound better than others, but they just do.
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