It would help your question when you tell us what your current body state and abilities are.
Medium aerobic abilities are needed, outstanding aerobic abilities may prevent people getting past the 'easy' to learn first 5 minutes men, 4 for women.
Bad conditioning
The trouble with high level aerobic training is that one teaches the body to have the wrong reaction to low O2.
Under stress and high O2 needs, the body learns to increase the Heart Rate. Freedivers want it to stay down.
Some modest aerobic training in combination with a healthy diet can help to loose weight, clean up the body, cardio vascular system, and mind. However to prevent it from interfering with my freediving, I would not push the envelope, and slow down when I feel I'm getting out of breath. That means jogging instead of running. Or in water, just a modest pace you could keep up 'forever'.
Easy fase, stuggle fase
In Freediving we have several fase's we go through. I just mention the two most important ones: Easy fase, stuggle fase.
The easy fase is where your body has plenty of O2 and works aerobically.
The struggle fase starts when tension and or contractions set in, from then on there is a scarcity of O2 and abundance of CO2. The muscles will get less O2, and will change over to work anaerobically. This slows down the overall metabolism(O2 burning), and allows relaxed freedivers to swim so far beyond the easy fase. Usually the first 50-75m are the easy fase, after that it's the anaerobic fase, which is tough but can be learned to be tolerated and even enjoyed.
What will happen if you have a high Aerobic ability?
Well your heart is conditioned to speeding up and pumping more volume to accommodate the muscles, who are also better supplied by more and bigger veins, and can better absorb the O2 out of the bloodstream. The result is that instead of slowing down the circulation, and transferring to anaerobic muscle work, the body stays longer in aerobic, consuming much more O2 and leaving much less for the brain and heart to use. The final result is that these divers have to give up
because they do not have enough O2 for their brain. They have very little or no 'leg burn' - acid build up, and recover quickly from their dives. Freedivers who have their body switch faster to 'freediving mode' will have their legs and other muscles feel like very heavy, even impossible to use, however they have still enough O2 in their bloodstream to sustain their heart and brain. Because their muscles are full of acid they can not do a similar dive without hours of recovery.
Due to the long and fast cycling to my job, I'm having a high aerobic ability, and therefore my dives have to end because of lack of O2 in circulation, whilst my muscles feel hardly no lactic acid at all.
I have a tall, slender body with little fat.
My advice is to seek to do a freediving course, and find dive buddies. Until you have those you can improve your swimming technique, build your neck weight, get a good freediving mask, snorkel and fins, read up on freediving, learn breathing and stretching and enjoy some
modest easy fase dives - provided you rebelliously abstain from hyperventilating and make sure you're rested and warm and hydrated.
