Wednesday 31 August 2011

How inspiratory muscle training (IMT) improves performance…in a nutshell

You can obtain more information about breathing training at, where you can also find out about my comprehensive guide to breathing and exercise “Breathe Strong, Perform Better” (published by Human Kinetics Inc.). Scroll to the bottom of this page to visit the ‘Breathe Strong’ Amazon store.

So, having cleared the air in my previous Blog, this second instalment provides an introduction to how IMT improves performance, and explains why it has nothing to do with maximal oxygen uptake (VO2max), or inhaling more oxygen (a common misconception).

Let’s start by returning to the question of what people believe they know about the role of breathing in exercise limitation, and why it’s only half of the story. We’ll begin by considering a factor that is synonymous with training and improved performance – maximal oxygen uptake (VO2max). Most lay people  ‘buy into’ IMT because they [incorrectly] assume that IMT increases the amount of oxygen in the blood, thereby increasing VO2max. It’s therefore a surprise to learn that breathing more DOESN’T do any of this (find out why below). On the other hand, sport scientists know that breathing more doesn’t increase VO2max, so they find it hard to understand how on earth IMT can possibly improve performance. So for many people who know about VO2max, the ‘knee-jerk’ response to the concept of IMT is to conclude that it can’t possibly work, i.e., because there is no obvious underlying mechanism. However, IMT improves performance via an entirely different mechanism to VO2max, but one that is, nonetheless, linked to oxygen delivery. I’ll provide more detail in a later Blog, but what follows is the ‘abridged’ version of how IMT improves performance. If you want to know the nitty-gritty detail, then please revisit my Blog, as I’ll be discussing this in due course. In the meantime, you can also find out more in my book, “Breathe Strong, Perform Better” (see or scroll to the bottom of this page to visit the ‘Breathe Strong’ Amazon store).

How IMT improves performance

Over the course of the past decade, an important cardiovascular reflex has been discovered. The reflex originates from the breathing muscles, and when it’s activated, it causes blood flow to the limbs to be restricted (a process known as vasoconstriction). Impairment of blood flow to exercising muscles reduces the delivery of oxygen and nutrients, as well as impairing the removal of metabolic by-products such as lactic acid. The reflex is activated when the breathing muscles are forced to work hard, or for prolonged periods, and it’s triggered by build-up of metabolic by-products in the breathing muscles (for this reason, it’s called a metaboreflex). The impairment of blood flow and oxygen delivery to limb muscles resulting from activation of the metaboreflex causes them to fatigue more quickly, thereby impairing performance. Research has now shown that the intensity of breathing work required to activate the metaboreflex can be increased by IMT. In other words, athletes can work harder, and longer before the metaboreflex causes blood flow to be directed away from their limbs. The result is that IMT improves performance in a wide range of sports and exercise modalities because it preserves oxygen delivery and metabolite removal from exercising muscles. It’s that simple, and that profound.

In addition to influencing the metaboreflex, IMT also makes breathing feel easier. Because the inspiratory muscles are stronger and more powerful after IMT, they are able to undertake the work of breathing more ‘comfortably’. In other words, the muscles are operating at a lower percentage of their maximum capacity, which makes the activity feel easier. For the same reason, being stronger also increases the endurance of the inspiratory muscles, delaying fatigue, and making breathing feel easier. Finally, because breathing feels easier, and because the limb muscles are better supplied with blood (delivering oxygen and removing metabolites), leg discomfort, and the sense of effort associated with exercise (perceived exertion) is also lower – athletes feel as though they are not working as hard.

Now you know how IMT does work, let’s finish by explaining why IMT does not increase VO2max.

Why breathing doesn’t limit VO2max

The transport of oxygen to the working muscles involves four stages:
1. Alveolar ventilation—Delivery of atmospheric air to the alveoli (breathing).
2. Pulmonary diffusion—Transfer of oxygen from the alveoli to the capillary blood.
3. Transport by the blood—Collection and delivery of oxygen in combination with the blood from the lungs to the muscles.
4. Tissue diffusion—Transfer of oxygen from the muscle capillary blood to the muscle cells.

There is no active transport of oxygen at any point in its journey from lungs to tissues. The entire journey occurs via a process of passive diffusion. During diffusion, oxygen moves from an area of high concentration (the atmosphere) to one of lower concentration (the muscle). The rate and efficiency of diffusion are directly related to the size of the gradient. Think of a river flowing downhill; the steeper the gradient of the hill, the faster the water flows.

In theory, any one of the four listed stages could limit the transport of oxygen. In practice, for people with healthy lungs who are at sea level (not at an altitude where the oxygen gradient is reduced), steps 1 and 2 operate with almost 100 percent efficiency in terms of their purpose, which is to oxygenate the blood fully before it leaves the lungs. Steps 1 and 2 are the only steps in the transport of oxygen that can be influenced by breathing, and because the blood is almost 100 percent saturated with oxygen when it leaves the lungs, increasing breathing cannot improve oxygen transport (the oxygenation of the blood is already almost 100 percent). In other words, breathing more cannot increase maximal oxygen uptake, and this is why people sometimes incorrectly jump to the conclusion that IMT cannot possibly improve performance. This is incorrect, so spread the word!

If you found my first blog interesting, please come back for further articles and news, as well as my musings on all things breathing and sport related. Also, don’t forget that you can obtain more information about breathing training at, where you can also find out about my comprehensive guide to breathing and exercise “Breathe Strong, Perform Better” (published by Human Kinetics Inc.). Scroll to the bottom of this page to visit the ‘Breathe Strong’ Amazon store.

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