Yesterday I had my weekly 20km paddle-tour to the kayakclub and back. The weather was very beautiful so I decided it was safe enough, regarding the crossing of the Alkmaardermeer, to paddle my old K1-racer today.
After having started I, developed the target for this evening: "working on my body-posture". Especially the position of my head&neck, as well as keeping my upper body straight while paddling.
This is related to my visits last months to a Mensendieck-therapist because of neck-problems. It turned out to be that pushing the head forward (something I clearly did so for years already) puts an enormous strain on the neck.
By reducing that, with help of Mensendieck and exercises, I managed to solve cq. reduce the problem in daily life. However while kayaking this turns out to be more difficult as it is not so easy to ban out the habits of a lifetime of paddling. As I noticed last years that I had a very tired neck after a heavy paddling day, sometimes even resulting in severe headaches 
, it is necessary to improve my paddling style as well. I am proceeding gradually however and evenings like this help a lot.
It feels a quite bit contradictionary, while pushing and pulling your paddle, to straighten your backbone, to push forward your breastbone and, as a result, hold your head higher.
I got the impression tonight that working on my posture also results in higher speed. But after realising sometimes ""Hé men, you´re cruising at 10km/h now
often the "FLOW" was gone immediately with a dropping speed as a result.
However focussing on posture helped quit a lot in getting "flow" again.
This is what I concluded:
- Making longer strokes results in higher speed than shorter ones at higher frequency.
- The longer stroke gets the biggest benefit in the forward part: starting more to the bow.
- Also important is that last part of each stroke: making it longer this results in more body-rotation.
- I should sit with straight upperbody while bending forward. This helps also in making the forward part of the stroke longer.
- Keeping the arms straight while paddling results in more rotation (obviously this is best possible with the wing-paddle)
- may be my paddleshaft is too short, regarding the tendency to paddle at a higher frequency.
- Last but not least: the stroke must feel good and preferably make no noise. May be this is the most important issue in this list.
What all this has to do with a GPS? Well, while using the speed-indicator from the GPS you get direct feedback on your paddle-technique and the things you try out, giving you a very fast learning curve.