Wave frog raises his body at two o'clock, and his arm presses water; The core strength of abdominal contraction. I don't agree. It's just too early to flip your hands and clamp your arms. The procedure should be to flip your hands, separate your arms, lift your elbows, press down, stroke backwards, clamp your arms, close your elbows and stretch forward.
The arm pressing water means that when the arm is opened from the forward sliding state, it is opened to the butterfly angle (the maximum opening angle) with shoulder force, and the arm is bent with high elbow, and directly pressed down with pectoral muscle force (note that it is not just to clamp the arm), and the high elbow is rowed backwards, and then the arm is clamped to close the elbow.
The core strength of tummy tuck is two concepts. One is abdomen, and the abdominal muscles should be tense and not relaxed. If the waist is relaxed, it will collapse, and the posture of the body in the water will change, increasing the sliding resistance. The second is the core strength. This concept is so important that most people have misunderstood it. The concept of core strength refers to a whole that has power in series and conduction from head to toe, and it is called core strength to use this whole body to exert strength.