We take breathing for granted, but breathing and basketball are inextricably linked. I'm not so self-absorbed to believe that there is only one way or a best way, but share what I've found helped players who are willing to take instruction.
"the more deeply you exhale, the calmer and more capable you become..." - Jocelyn Glei
1. Centering breaths are part of Jason Selk's recommended "Ten-Minute Toughness" sports psychology routine. The broader routine includes centering breath, identity statement (this is who I am), mental highlight reel, performance statement (this is how I play), and centering breath.
Air doesn't "enter" the diaphragm, which is a muscle. The diaphragm contracts (shortens), which lifts and spreads the chest cavity and produces negative pressure in the space between the lungs and chest wall. This allows air to flow passively into the chest. Controlled breathing tends to reduce anxiety and accompanying shortness of breath.
2. Quick Physiology lesson. Heart and lung performance are linked to provide oxygen to working muscles. This can be measured with a "metabolic cart" measuring expired gases (oxygen and carbon dioxide) to calculate 'oxygen consumption' (VO2) and examine the relationships between heart and lung performance. Ordinarily, we are NOT limited by breathing but by our ability to deliver oxygen to working muscles, a function of heart performance. When our metabolism becomes anaerobic (not enough oxygen delivered), lactic acid builds in muscle (burning feeling in the legs), and we compensate by breathing faster (hyperventilation) to eliminate carbon dioxide and control body acidity (pH).
3. The Cooper 12-minute run correlates with VO2max, the number that is the best measurement for cardiorespiratory (heart and lung) fitness. The last time I did this (age 59), I overtaxed my ankles and actually had a health setback...and obviously this can set off problems for individuals with heart, lung, or orthopedic issues. Check with your physician...
4. We differential abdominal versus thoracic breathing. Abdominal breathing tends to be deeper and slower. Abdominal or 'diaphragmatic' breathing is believed to aid in relaxation.
We use the expression: "take a breath", meaning slow down and don't get ahead of yourself.
5. Practical application. Free throw shooting. Aside from the mechanics itself, this is how I teach young players to approach a free throw. Do not go to the line until you are ready to receive the ball. This helps avoid "freezing up." Visualize the shot going in. Receive the ball and take your pre-shot routine. I favor three dribbles and a good breath and full exhalation.
Targeting happens simultaneously. I don't like players 'spinning' the ball. I don't want players 'actively breathing' (inhaling or exhaling) during the shot itself. Every shot is therefore taken after full exhalation. Get players to focus on the 'process' not the outcome of the shot.
Ronald Paul Sen, M.D., F.C.C.P. (Fellow, American College of Chest Physicians)