Thursday, 17 November 2011

If it ain’t broke don’t fix it?

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.

As a scientist, I feel a duty to exploit new knowledge to drive innovation, and in doing so, to make things better. So when someone tells me that, “the POWERbreathe works perfectly well”, and cautions me, “if it ain’t broke don’t fix it”, my natural response is to say, “it’s good, but it could be even better”.

In this Blog I thought I’d share with you some of the scientific insights that led to the development and launch of one of the most exciting new training products to hit the market in a very long time…the POWERbreathe® K-Series. (but then I would say that, wouldn’t I?)

The birth of POWERbreathe®

When I first conceived the idea for the POWERbreathe® in the late 1980s, we knew comparatively little about how to train the breathing muscles. However, what was abundantly clear was that the devices that preceded POWERbreathe® didn’t work very well. Early products were very crude; they generated training loads using simple, static flow resistors, which were akin to breathing through a straw. In other words, they made breathing harder by passing inhaled air through small holes with fixed diameters. This type of breathing training is known as inspiratory flow resistive loading (IFRL) and typical training products allow users to select from a range of different sized holes that occlude the inspiratory port of the device. In theory, for a given rate of inhalation, the smaller the orifice, the greater the load to breathing. In practice, the training load doesn’t just vary with the size of the hole, it also varies with the rate of airflow; the faster one breathes through a given hole, the harder it is to inhale, and vice versa for slow inhalation. This makes IFRL is a bit like pulling a trolley loaded with passengers who keep jumping on and off the trolley; the load is never constant, or predictable. For this reason, IFRL fell out of fashion, and whilst some IFRL products still persist in the market, the primary reason for their continued existence is their low manufacturing cost, because their efficacy is highly questionable.

So, at the time that I undertook my first breathing training studies, there was nothing in the market that met my need for a device that delivered an effective training stimulus to the inspiratory muscles. Without any commercialisation agenda (see Blog 1), I therefore set about creating a training device that would provide that most important requirement for any device that is to be used to train muscles - a reliable load. The resulting device was a little “Heath Robinson”, but it imposed a reliable inspiratory resistance using a spring-loaded valve, and became the precursor to the mechanical POWERbreathe® range.

The drive to optimise

As knowledge and understanding of the inspiratory muscles increased, it became apparent (to me at least) that the inherent characteristics of the load provided by the mechanical POWERbreathe® were not optimised. Why so you might ask, surely all you need is a reliable load, a suitable training regimen, and the muscles will do the rest? That’s true up to a point, but effective is not the same as optimal, and I wanted optimal. In order to understand my discontentment with the loading provided by the mechanical POWERbreathe®, it is necessary to delve into some fundamental muscle physiology.

Muscles have a number of inherent properties, which if they are overlooked, can impose limitations upon their ability to adapt to training. One of the most important is the fact that the force generating capacity (strength) of muscles varies, depending upon their length. For example, the biceps is weakest when the elbow is fully extended, becomes stronger as the elbow flexes, and then becomes weaker again at full flexion. This property is known as the ‘length-tension’ relationship, and it was first described in detail by an English physiologist called A.V. Hill in the 1930s. Most modern gym weight training machines incorporate a cam system that accommodates the ‘length-tension’ properties of the muscle group being trained. This innovation makes it possible to overload muscles maximally, and also maximises the number of repetitions that can be achieved.

In the context of the breathing muscles, their ‘length-tension’ relationship determines the tension (force) they can generate at any given lung volume. Since we cannot measure the force generated by the respiratory muscles directly, the relationship is expressed as a ‘volume-pressure’ relationship. As might be predicted, the inspiratory muscles are strongest when the lungs are empty, and the expiratory muscles are strongest when they are full. But this relationship is so potent that the inspiratory and expiratory muscles have little or no pressure generating capacity at their weakest lung volumes (see Figure 1 below for the inspiratory muscles). This phenomenon is also known as “functional weakening”.

Figure 1. Strength (pressure) vs. lung volume for the inspiratory muscles. Note there is functional weakening as lung volume increases.

The practical implications of functional weakening are not obvious at first sight, but they have a profound influence on how the inspiratory muscles respond to a load of fixed intensity (like that provided by a mechanical POWERbreathe®). The problem with fixed intensity inspiratory load is that its relative intensity increases with lung volume. In other words, as the muscles become weaker throughout inhalation, the relative intensity of the load increases. For example, when the lungs are empty, and the inspiratory muscles are strong, the load might be only 50% of the maximal strength. As inhalation progresses, the muscles become functionally weaker, and this same absolute load becomes a progressively greater and greater proportion of the strength of the muscles. Finally, the load exceeds the maximal strength of the muscles at that lung volume, and inhalation must cease. This leads to a phenomenon that I call “breath clipping’.

In the Figure 2, the implications of the changing relative intensity of a fixed load are clearer.  It illustrates the interactions between inspiratory muscle strength (black line), different training loads (40%, 50%, 60% and 70% of maximal inspiratory muscle strength [coloured lines]) and the breath volume that can be achieved during training, as well as the effect of fatigue (dotted lines). For example, at a load of 40%, it is possible to inhale to around 60% of lung volume, whereas at a load of 70% it is only possible to inhale to around 35% of lung volume before the breath is clipped. This is equivalent to being restricted to the first 35 degrees of elbow flexion of a bicep curl – not very satisfactory.

Figure 2. The interactions between inspiratory muscle strength (black line), different training loads (coloured lines). The slopes on the coloured lines illustrate how the relative intensity of the load increases during inhalation.

The paradox of heavy loading

So, what are the practical implications of functional weakening and the breath clipping that results? Although muscle is a very adaptable tissue, research has shown that the adaptations elicited by inspiratory muscle training are specific to a number of characteristics of the training stimulus (Romer & McConnell, 2003 -, including the lung volume at which training takes place. The practical implication of this is that optimal results are only achieved if inspiratory muscle training is undertaken across the full range of lung volume, i.e., from the point at which the lungs are as empty as they can be, to the point at which they are full. Failure to do this will lead to sub-optimal adaptation at some lung volumes, which may have a performance impact if these volumes are called upon during exercise. As can be seen in Figure 2, if the load is too heavy, it’s not possible to train across the full range of lung volume, and the heavier the load, the lower this range is. Furthermore, when you add fatigue into the mix, it becomes even worse.

In addition, loading too heavily can also compromise the amount of work that can be undertaken during training, which also impairs the training response. In a recently published study (McConnell & Griffiths, 2010 -, we examined the effects of various inspiratory loads upon a range of different variables, including the number of repetitions that could be tolerated, the volume of each breath during the training session, the amount of work completed during the session, and whether the session activated the inspiratory muscle metaboreflex (see Blog 2 for information about this important reflex). We studied well-trained young rowers who had not undergone any IMT previously. As expected, the number of breaths (reps) declined as load increased (e.g., just 4 breaths at 90% of maximal inspiratory muscle strength and 84 breaths at 60%), and the volume of each breath declined with increasing load, as well as during each session (because of fatigue). The most surprising finding was the influence of heavy loads (>70%) upon the amount of work that was undertaken per breath (work is equivalent to the load multiplied by the breath volume). Because the volume of each breath was lower with heavy loads, the amount of work done per breath was reduced markedly. This effect is completely counter-intuitive, because during limb muscle training, heavier loads mean more work (that’s because if you’re maintaining good form, the range of movement doesn’t change a great deal when moving from moderate to heavy loads). The detrimental effect of the reduction in breath volume upon the training stimulus delivered to the inspiratory muscles was compounded by the reduction in the number of breaths at heavy loads. In other words, the total amount of work done by the inspiratory muscles is reduced markedly by increasing the load above 70%. This finding explained some confusing results from previous, unpublished studies undertaken by two of my Masters students. In two separate studies, we noted that professional rugby players, and professional soccer players showed virtually no change in inspiratory muscle function in response to training at loads in excess of 70%. So you can have too much of a good thing!

It should be apparent by now that, although the mechanical POWERbreathe® ain’t broke (it works extremely well), it could benefit from some improvement. The optimal training device would be one that enabled heavy loading, without compromising lung volume achieved, and work done.  That was the conclusion I reached in 1997, and it sparked an ambition in me to develop the “perfect POWERbreathe®”.  Somewhat frustratingly, it has taken more than a decade to realise my original vision, but it’s finally here.

Designing the “perfect POWERbreathe®”

From the preceding paragraphs, it should be apparent that in order to deliver an optimised training load, the perfect POWERbreathe® must do the following -

1.  Promote maximal volume excursion

2. Promote maximal load setting without compromising volume

3. Maximise the amount of work undertaken during a given training session

As luck would have it, all of these requirements can be satisfied by a loading mechanism that is sympathetic to functional weakening of the breathing muscles (Figure 1). In other words, rather than maintaining the same absolute load throughout the breath, it maintains the same relative load, i.e., despite functional weakening, the load starts at 50% of the strength, and ends at 50%. To achieve this the device needs to taper the absolute load during inhalation, so that it is the same shape as Figure 1 (above).

The POWERbreathe K-Series is born…

The POWERbreathe® K-Series (PBK) does precisely what the physiology specified for the perfect POWERbreathe® - it provides a tapered load that optimises breath volume, work and tolerability during training.

The PBK design is a departure from the spring-loaded valve technology of the past, favouring instead, real-time, dynamic adjustment of a flow resistor valve. In essence, the surface area of a variable flow orifice is adjusted within each breath according to the prevailing respiratory flow rate.  It’s the world’s first dynamically adjusted flow resistance trainer, and it is the result of a long-term collaboration between POWERbreathe®, myself and colleagues at Brunel University in London.

Adjustments to the valve are made 500 per second, taking less than a millisecond to complete (see video clip 1 below). This means that, in theory, ANY pressure load profile can be imposed. In practice, a tapered load akin to that in Figure 1 is provided (see video clip 2 below). This allows for maximal volume excursion, and a considerable improvement in tolerability, which enhances the number of breaths before ‘failure’. Trials have also revealed that at loads above 50% of inspiratory muscle strength, the amount of work completed per breath is greater using the PBK than when using the mechanical POWERbreathe®. The tapered load also permits ‘heavier’ loading, improving the amount of work done per breath still further.

videoVideo Clip 1: PBK valve adjusting at 500 times per second

The first PBK products were launched in 2010, and real-time PC connectivity via POWERbreathe®’s unique BreatheLink® software came on stream just this month. The BreatheLink® software is a revelation, even for me. You can observe key functional indices in real time as you train, which makes it possible to correct bad technique, as well as focussing on maximising key variables such as volume and airflow rate.  Even I’ve noticed how much better my technique has become over the period I’ve been test-driving the BreatheLink® software. More importantly (and remarkably), I even notice an improvement in how my breathing feels under ‘stress’, such as during interval and hill training. That’s amazing, given that I’m the longest serving member of the POWERbreathe® training club! It’s VERY addictive…see the video below for a quick peak…

videoVideo Clip 2: BreatheLink® software providing continuous feedback during PBK training. Top left panel is the training load during each breath.

Of the many unique and innovative features offered by the PBK, its auto load setting utility is one that many users will find especially helpful. Every training session starts with two unloaded set-up breaths, during which the user must exert maximal effort to inhale as quickly and deeply as possible. These set-up breaths provide data that are used to calculate an index of inspiratory muscle function, and a measurement of lung volume. In “Automatic” mode, the former is used to automatically programme the appropriate training load; the latter is used to provide a personalised taper for the training session. This means that the loading of each and every training session is optimised to the prevailing function of the inspiratory muscles. Of course, it’s also possible to set your load manually, and with the BreatheLink® software it’s even possible to create your own training sessions, and to upload these to the PBK unit. I’ve been experimenting with some interval training sessions using this facility. Needless to say, the ability to make within and between breath adjustments makes this type of device extremely versatile from the loading perspective.

More than a decade after concluding POWERbreathe® was “good, but could be better”, I finally have my perfect POWERbreathe® - it’s taken longer than I expected, but it’s been well worth the wait – there’s virtually nothing that the PBK and BreatheLink® software cannot deliver...
        …breathing training really has become 

          “a piece of cake”.


Look out for the FREE Breathe Strong Foundation Training App on iTunes at the end of the month.

If you found my 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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