On the surface it may seem like a paradox that someone can simultaneously display cardiovascular fitness and disordered breathing patterns. In the pursuit of enhanced performance – we engage in various forms of cardiovascular training. Depending on the intensity and type of training, significant demand can be placed on muscles with overlapping roles. These roles may include breathing, postural control and physical performance.
Pushing physical performance elevates respiratory drive through multiple interdependent pathways. Elevated respiratory drive co-opts postural and shoulder girdles muscles to act as accessory breathing muscles. This pattern of use is an appropriate adaptation to increased levels of physical performance, but is maladaptive in other contexts (e.g. during normal activities or rest). It is not uncommon for recreational and highly driven athletes to develop tense wiry neck and shoulder girdle muscles – which may unnecessarily engage while breathing at rest.
Extreme demand on the diaphragm, not only compels the body to engage accessory breathing muscles, it also shunts and diverts blood to the diaphragm – this is called the metaboreflex. This reflex diverts blood flow from the lower limbs and spinal stabilisers to the diaphragm – ironically both of these responses quickly erode performance and increases the risk of injury.
Research into inspiratory muscle training shows that the metaboreflex can be blunted and delayed with training. Inspiratory muscle training is not a solution to the habitual engagement of accessory breathing muscles. Training inspiratory muscles would amount to the superimposition of ‘fitness on dysfunction’.
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J.D Witt et al: Inspiratory muscle training attenuates the human respiratory muscle metaboreflex (2007).