Breathing and stretching play an important role in influencing your mental state, emotionally, and physically. It is well known that in sports such as javelin, shot put, archery, and other sports that involve throwing or shooting, that the timing of the breath is crucial to success.
The mechanics of breathing is such that it influences your pulse, and blood pressure. Inhaling reduces intra-thoracic pressure, bringing more blood back to the heart that the heart in turn must pump with increased rate or increased volume. On exhaling, intra-thoracic pressure is increased which slows blood return, and hence heart output. This is a normal fluctuation that occurs during everyday activities as well as sports.
It is difficult to relax if you are breathing rapidly. If you breath more rapidly you also start to use accessory muscles of respiration ( scalene, pectorals, etc.) This increased effort heightens the sympathetic nervous system which affects muscle response and viscoelasticity.
By concentrating on breathing, athletes will increase body awareness. By focusing on your breath it allows you to ease into the new range of motion.
We can take this knowledge of how muscle tension is affected by breathing and apply it to stretching. Through relaxed breathing techniques we can release tension and concentrate on the tissues being stretched. As you exhale, your diaphragm relaxes, and your heart slows. This is the best time to lean into a stretch.
If you find your breathing is becoming more labored or you are holding your breath then you need to back off and work on a stretch that is less demanding.