Thanks to Total Immersion way I could swim 10k in 3h20min in swimming pool without stops. I felt the most waste of energy during the flip turns

I am 39 years old and 1.80m toll. I believe the Technic could be improved. I normally don’t have the training focus on TI Drills, I just make 2 beat kick and control the number of strokes per length, which is 18~20 for each 25m. I believe this SPL can be improved. If i focus only in SPL and make only one length it can reach 13~15 with 1.30s per stroke. But to achieve this the stroke is not relaxed. Because that, when the length count increases, the SPL increases as well.