There are several factors that influence the achievement of a good dive in a state of apnea. Freediving is mostly based on mental training, then physical ability, followed by good technique and the use of appropriate equipment. The key to freediving is to remain relaxed underwater and maintain a slow heartbeat while delivering adequate oxygen to vital organs in your body. Naturally, when we exercise our heart rate increases to compensate for the higher oxygen demand by our muscles. In freediving, however, the goal is to minimize oxygen consumption in terms of efficiency. Sustaining a low heart rate at the same time as doing physical activity not only requires strong mental training, but good physical conditioning as well. A strong comfort in water is also required in order to remain relaxed and alert.
Mental training helps overcome and control tension, fears and possibly apprehension when freediving. Jacques Mayol used tibetans relaxation techniques. Francisco "Pipin" Ferreira Rodrigues uses yoga and Umberto Pelizzare uses yoga and self-suggestion. In the practice of yoga the pranayama is the mental control of the breathing. This is the yoguic respiration. Proper respiration must be diaphragmatic and thoracic. When inhaling your abdomen must protrude and then your thorax should lift up, in that way the alveoli will fill up. A good book about yoga could be useful when learning about the pranayama and how to control breathing. The purpose of using yoga and other relaxation techniques all focus on one thing lowering your heart rate. During deep dives Pipins heart rate has been measured as low as 4 beats per minute.
The ability of the diver to control the psychological activity under water is quite important for the protection of their life and health. That is why one must have a good psychological preparation to ensure psychological alertness. A diver's psychological alertness is determined by the status of his own cognitive abilities - the level of the attention, perception, thought, memory, and prediction of deeds and situations.
Most freediving training occurs is in the pool. There are two main aspects of training, static apnea and dynamic apnea. Within dynamic apnea training: long and short recovery times are used to enhance the bodys use of oxygen. In the short recovery phase the exercise is faster and the resting time is shorter, whereas the apnea is shorter. In the long recovery phase the exercise is slower and the resting time is longer so the apnea is longer. I recommended starting with short recovery apnea to condition the body to the build up of high levels of lactic acid that occur during breath-hold dives. Eventually, longer recovery apneas can be used to train for longer bottom times.
Descending techniques: Before a breath-hold dive, you should be relaxed floating on the surface taking slow, deep, quiet breaths. In the final moments before the descent you should breath just 4 times in a minute (as a guide). It is important to be familiar with the physiological effects of hyperventilation before attempting a breath hold dive, because improper hyperventilation is extremely dangerous (refer to hyperventilation link on the side bar). For your last breath, forcefully exhale to the maximum and then fill your lungs to capacity. While pre-equalizing your ears, initiate some forward momentum then bend your body at the waist lifting one leg in the air to enter into the water in a vertical position. You must sink without movements until your fins are under the surface. At this moment start to kick, release the snorkel (optional) and start to equalize. After a few meters, little effort is needed to glide deeper underwater.
Ascending techniques: The best hydrodynamic position for ascent is to keep your hands together and over your head. Don't look up or down and swim as fast as you can. You must keep your eyes in the line for reference. After a long dive, it is common practice to exhale slightly as you approach the surface (refer to the shallow water blackout section in the physiology link).
Regulation of breathing is of vital importance when trying to relax. It is necessary to decrease the frequency of breathing and increase the duration of exhaling. After inhaling, the air is held in the lungs for a few seconds and then is slowly exhaled. This slow rhythmic breathing cycle helps calm the body. The relaxation is usually performed with closed eyes and relaxed body. The relaxation state should be similar to that of sleeping but without the drowsiness. The muscles of the limbs and the torso are slackened. Consequently, a notion of heaviness, calm breathing, rhythmic pulse, warmth of body, and coolness of the forehead are triggered. Relaxation can take anywhere from 5 to 20 minutes. Finally, the relaxation doesn't end when immersed in water, the diver must have a continuing comfort in water in order to conserve oxygen and remain alert and prepared.
The ability to equalize pressure with the surrounding water is of paramount importance in freediving. Without proper equalization, pressures greater than a few meters (~10 feet) of water become unbearable due to pressure differentials in the sinuses and inner ear. Moreover, without proper mask equalization, the compressed air under the faceplate will painfully crush the mask to your face as you descend. It is important to remember, that for successful ear clearing, one must clear early, often and gently. Don't force clearing and don't dive with a cold.
Interestingly, while pressure increases linearly with depth, the volume change in the sinuses and inner ear, resulting from these pressure changes are not linear (Figure: % Volume Change with Depth). Therefore, it is more difficult to equalize the pressure in the first ten meters than after 100 meters.
For more information on the physiology of equalizing, refer to the discussion of barotrauma in the diving physiology section.
Antonio Valsalva lived in the 1700's and was the first to record a technique for pressurization of the middle ears. With the nostrils pinched closed, pressure is increased in the chest. An attempt is made to blow out the closed nostrils and cheek muscles are kept tight and retracted, not puffed out. With this technique, gradients of 6-10' of sea water can be achieved. This technique does have some disadvantages, however, as prolonged effort can cause venous engorgement of the tissues around the Eustachian tubes. It also causes a decrease in venous return to the heart and can lower blood pressure if the effort is prolonged. It does seem to be the easiest and most intuitive of the techniques and usually is what a students will perform on their own with no other training.
Herman Frenzel was a Luftwaffe commander who taught this technique to dive bomber pilots during WW2. The pressure changes in commercial aviation are usually much more gentle and occur more slowly than in diving. A dive bomber pilot will experience pressure changes more rapidly however, much the same as in diving. The technique developed for flying is to close off the vocal cords, as though you are about to lift a heavy weight. The nostrils are pinched closed and an effort is made to make a "K" or guttural "guh" sound. By doing this you raise the back 1/3 of the tongue and the "Adams Apple" will elevate. For this reason I call the technique the "throat piston". A diver is actually making a piston out of the back of the tongue, pushing it upward. This maneuver compresses air in the back of the throat and the pressurization effort can be seen in the fleshy tissues of the nose. A student may practice the technique by watching the nose inflate and by watching the "Adams Apple" move up and down. Bobbing the "Adams Apple" is good practice for dive bomber pilots and scuba divers alike. This technique is actually my preferred pressurization maneuver as it can be done anytime during the respiratory cycle and it does not inhibit venous return to the heart. The effort is usually brief and can be repeated may times quickly.
Joseph Toynbee lived in the 1800's and as you recall, he first identified the crackling sound present in ones head with the anatomic opening of the Eustachian tube during swallowing. His technique is to pinch nostrils shut while swallowing. The muscles in the back of the throat pull open the Eustachian tube and allow air to equalize if a gradient is present. Swallowing can be difficult for the novice diver, especially while breathing dry air. This technique is not recommended for rapid descent as there is no margin for error if the Eustachian tube does not equalize on first effort. If a middle ear squeeze is already occurring, it will be more difficult for the Eustachian tube to be pulled open.
Presented at the 23rd Annual Undersea and Hyperbaric Medical Society, Pacific Chapter meeting (Seattle, WA 1995) by Edmond Kay, MD