Creatine phosphate is the ideal energy source for apnea exercise. Your body can store enough creatine phosphate for 5 seconds of 100% maximal exercise, which converts to as much as 2 minutes of submaximal diving style movements.
Seals and marine mammals have vastly higher creatine concentrations in their muscles and use it as a primary fuel during dives.
Upon depleting the creatine phosphate energy reserve, about 50% of it is regenerated within 60-seconds of recovery breathing. After 5 minutes of recovery 90% of the creatine phosphate has been regenerated.
The fact that higher muscle creatine can effect weight training has very little to do with freediving---in the sense that the PRIMARY gain of higher creatine by far is the instant energy it provides without the use of oxygen or carbohydrates. Burning creatine phosphote stored in muscles produces no byproducts such as CO2 or lactic acid. It is a totally 'clean burning' fuel, the only drawback is you can only store a limited amount of it.
Anaerobic training will naturally cause a huge increase in muscle creatine concentrations.
As an example, during a 10-sec 100m sprint by a world class sprinter, 50% of the energy comes from creatine phosphate, 50% comes from stored ATP, and virtually 0% comes from glycogen (carbohydrates). This is why a 10-sec sprint doesn't produce lactic acid; to produce lactic acid requires burning carbohydrates.
Another example:
During a 100m sprint:
- The first 5 seconds burn pure ATP
- Then, the ATP stored is exhausted
- Then, the creatine phosphate in the muscles is consumed as it regenerates the ATP store
- The ATP store is basically back to normal now, but all the creatine phosphate has been broken down into creatine and phosphate
- You now can burn the ATP with 5 more seconds of sprinting
- Now you have exhausted all your ATP and all your creatine phosphate, so you must start to burn carbohydrates which produces lactic acid and will try to consume oxygen as well
If you stop after 10 seconds of sprinting, the reason you are out of breath is because your body is trying to regenerate the creatine phosphate and ATP, and it is trying to regenerate those by burning carbs to produce ATP, which in turn restores your ATP store and also rebuilds the creatine phosphate molecules.