This is certainly relevant to aikido, and in particular the somewhat nebulous concept of "aiki". Unnecessary tension in a technique creates a reaction in your partner which tends to block things. Skilled practitioners make things look effortless, and use much less tension - they are more relaxed. It's a fascinating study - and lots of fun. Very different sport - but check Shane Benzies and his books and videos on running and technique - how technique makes a huge difference, with less effort.