steevke:
.39 cuft/min is, for a male, very low...
I agree with the others, if you are getting headache, then you are probably having CO2 build-up.
Me: Male, age 50, height 6 ft, weight 148.2 pounds, reasonably fit. SUUNTO Dive Manager calculates me with a SAC at 0.39 to 0.42 depending upon currents. My best SAC was 0.37 on some particularly mellow and in the zone dives..
Breathing technique? None, I just breath normally, not puffing, not blowing, not skip breathing. Just breathing like I am sitting at my computer. I also just slowly fin along.
I believe far to much effort is put into so called breathing technique. While I will agree it is a factor. If you are taking chest heaving breaths, you are going to blow through a lot of air, and quick. But, a lot of improvement in SAC can be achieved by the following:
1. Proper weighting
2. Perfecting your buoyancy control of which item 1 plays a major role.
3. Exercise. Conditioned and toned mussels will use less oxygen than the out of shape ones.
4. Do not use your hands! Keep them still unless reaching for or pointing at something. Hands are not efferent at propulsion. Those long things on your feet work so much better at this.
5. Dive often. Getting comfortable in the water will help with the heavy breathing.
6. Do not skip breath, do not breathe rapid and shallow. Take what I would describe as normal breaths, slow in and slow out.
7. Move in S-L-O-W motion. I swim slow, I move everything slow. Water is dense, trying to move anything fast uses more energy and that means more air.
8. Streamline everything, reduce drag.