1. Stay Warm
If you dive uninsulated, you’re heating the lake or ocean with your body, which increases your metabolism and oxygen-burn rates. Experiment with different amounts of protection. You want to stay warm during the dive but not overheat when you're not yet in the water.
2. Go Slowly
Rapid, jerky movements burn more air due to increased resistance underwater. You might actually see more around you when you slow down. Scuba diving is not a race.
3. Look, Ma, No Arms!
Imagine you have huge huge legs and tiny little arms, a T.Rex of the sea. Waving your arms and hands around burns incremental air, but won't affect your speed or your position.
4. Trim Up
Poor weight distribution creates increased drag and burns more air. So does loose gear. Try varying weight positions to get a more horizontal trim.
5. How Slow is Slow Breathing?
Try inhaling over a five- to seven-second period, and then exhaling over a six- to eight-second period. As a slower rate becomes more natural, you’ll no longer need to count. Don't hold your breath, though.
6. Reverse the Pause
If you pause at the top of our inhalation cycle, with our lungs full — instead of at the bottom of the cycle, as we usually do on land — it allows our bodies to extract a bit more oxygen from the air in our lungs.
7. Restrict the Flow
Try this: Hold your tongue against the roof of your mouth and breathe around the sides of your tongue. This artificially created restriction will force you to breathe in more slowly.
As with any sport, performance improvements come with practice.