One of the under-appreciated benefits of mixed-modal training may well be it’s ability to challenge the inspiratory muscles of respiration in a way that other modalities cannot. At the same time, this is probably still a big limiter for many athletes.
These muscles (the diaphragm and others) are responsible for both both breathing and postural (core) stability under load. This is why, after a tough workout, athletes will fold over or lean on something or even lie on the ground. Doing so removes the postural demands on these exhausted muscles and lets them concentrate on just breathing.
Research shows that these muscles can become significantly fatigued during intense efforts. When the inspiratory muscles become fatigued beyond a certain point, what is known as the inspiratory metaboreflex is triggered – basically, a reflexive shutdown of blood flow to the limb muscles. (sympathetic activation causing vasoconstriction) With this reduced blood supply, and along with it reduced oxygen, the perceived effort goes up as anaerobic processes begin to dominate and you are forced to slow. (this is likely a protective response to keep you from going faster than your breathing can handle) In other words, your legs may feel heavy not because they are actually fatigued, but because fatigue in your breathing muscles has triggered a reflex to shut them down.
Strengthening the inspiratory muscles can delay the initiation of this reflex, allowing for increased performance at a lower perceived effort.
Some points and also some of my thoughts relating to this:
1) High intensity conditioning sessions do not optimally strengthen the inspiratory muscles. It becomes impossible to spend enough time at a high enough intensity to develop them fully. (McConnell, 2011 – “Breathe Strong, Perform Better”)
2) Heavy mixed-modal circuits probably provide the strongest stimulus possible outside of direct training of the breathing muscles. The simultaneous heavy demands of core stability under high breathing that is seen in heavy “CP battery” type workouts is likely a stronger stimulus than can be provided by any monostructural activity.
3) This may be one of the reasons that mixed-modal trained athletes often do pretty well in endurance sports they’ve done little training in – a delayed inspiratory metaboreflex, allowing higher rates of sustained effort.
4) Even so, this probably doesn’t train the inspiratory muscles optimally. Furthermore, performing this type of training (eg: heavy “metcons”) for breathing development is very taxing both metabolically and to the CNS, and comes with a cost.
5) Engaging this reflex is a significant stressor, and probably not a good idea if one is training for health or longevity.
I’m experimenting with training to address this and will periodically post some updates. I’m still just beginning to learn more about breathing as a limiter.
Also, more tomorrow on off-season programming…..