I've been modifying my form this year. I have been following the message in this video to improve my form. I have been feeling pretty healthy and quite a bit faster. Despite going faster I typically get a bit less tired because I am being more efficient.
I would say my main issue in experimenting with this new form is being a bit too robotic. So I have been working to loosen up.
These efficiencies really helped me last weekend in my first trail running race, which I will write about soon.