Have you done any rowing? There is certainly some technique involved and you can't be all tensed up. But at the highest levels everyone has excellent technique. As an endurance sport, performance largely comes down to VO2 Max and pain tolerance, plus a bit from height.
My go-to golf philosophy book is "Cheng Hsin: The Principles of Effortless Power":
> To relax, you must surrender your mind-even the notion that you have a mind. You will find that relaxing your mind is the same thing as relaxing your body. There should be no separation between your mind's activity and your feeling-awareness of bodily sensations and impulses. Feel yourself letting go so that your body isn't "held" so much--this requires doing the same thing with your mind. When you relax your tissues, nervous system, organs, the muscles around your organs, every-thing, then the energy will flow. It is this very relaxation that allows for the energy, or feeling-attention inherent in your body-being, to circulate, develop, and be utilized.
Don't know how this affects daily writing ;)