A lot goes on in our physiological system during heavy exercise that we may or may not think about or be aware of.  In normal breathing the latissimus dorsi or commonly referred to as lats are active briefly during very deep inhalations and inhalation against resistance.  During exhalation they become active again when air is expelled with great force.  When swimmers and climbers experience latissimus fatigue their respiration changes and they notice it.

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Pendulum Lat Combo Pull

The sternocleidomastoid neck muscles support inhalation when lung volume nears 100% of vital capacity in deep breathing or when exercise is very rapid.  The scalene neck muscles help by lifting our ribs to get more air in our lungs.  In a 2013 study in Advances in Experimental Medicine and Biology researches looked at the electromyographic activity of a series of muscles involved in respiration to fatigue.  They found that early signs of respiratory fatigue could actually be found by examining the fatigue rate of the sternocleidomastoid and scalenes.  In other words when the musculature of the neck begins to fatigue due to heavy breathing soon the athlete will falter. 

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Pendulum 5-Way Neck

A well organized athletic program must include the development of the upper back and neck to maximize performance whether you are running or doing any activity that requires heavy breathing.