Some time ago exercise physiologists thought that the VO2max was the single determinant of human exercise performance in the respiratory system, assuming that maximal ventilation could be maintained indefinitely.

Nowadays it is known that inspiratory muscles tire with exercise, and that the increased work of breathing during exercise also demands higher blood flow from the circulatory system in order to sustain muscle contraction. This effect is called “inspiratory muscle metaboreflex”, and is caused by the accumulation of metabolites in the respiratory muscles, which trigger a widespread vasoconstriction in order to allow a higher blood flow in the lungs.

Muscle fatigue and vasoconstriction are limiting factors of physical performance, and give way to the so-called respiratory muscle fatigue, or RMF, firstly described in marathon runners during the 1980s.

Measuring maximal inspiratory pressure (MIP) it was found that after running a marathon there was a fall in MIP, with no alteration in the maximal expiratory pressure (MEP). Consequently they talked about an inspiratory muscle fatigue, or IMF, without expiratory muscle fatigue, or EMF.

The overall effect would be:

                                                           RMF = IMF + EMF

               (Respiratory Muscle Fatigue = Inspiratory Muscle Fatigue + Expiratory Muscle Fatigue)

When using a ventilator to help with the inspiration process during breathing it was found a 4.3% increase in leg blood flow. On the contrary, when the ventilator was used to add resistance to the breathing process, leg blood flow decreased by 7%, worsening leg fatigue.

There is evidence that strengthening of respiratory muscles can potentially improve physical performance. The strengthening procedures are defined as respiratory muscle training, or RMT, and they could be focused on inspiratory or expiratory muscles, therefore distinguishing between IMT (Inspiratory Muscle Training) and EMT (Expiratory Muscle Training).

Among the physiological effects to consider after RMT:

  • diaphragm hypertrophy
  • change of muscle fibers (increasing proportion of type I and size of type II)
  • improved neural control of respiratory muscles
  • increased respiratory muscle economy (reducing work of breathing)
  • attenuation of the respiratory muscle metaboreflex (therefore preventing blood diversion away from limbs)
  • decrease in perceived breathlessness and exertion (allowing longer exercise times until exhaustion)

RMT exercises can have exercise intensity fixed, with the physical activity carried away until exhaustion, or time trials. Time to exhaustion is sensitive to small physiological improvements, making it a good indicator of training procedures.

Among the methods we could talk about:

  • Endurance training, using voluntary hyperpnea. It involves recruiting respiratory muscles during deep breaths. It requires to learn correctly the techniques, used in many relaxing/meditation procedures.
  • Resistance training, with external loads in mouth position. It involves using a device, with many commercially available. One of the most popular categories is the linear pressure resistors (LPR), which are affordable and can be easily used in training.

The LPR devices facilitate IMT, as they offer different resistance levels and a chance of evaluation and exercise prescription.

In disease patients and healthy individuals IMT improved physical performance, mainly by improving blood flow distribution.

For athletes, with usually good respiratory function due to years of training, there is no clear protocol defined. Also there are differences depending on the sport type. In aquatic and intermittent disciplines (basketball, football, tennis, etc) the energy is mainly coming from glycolytic pathways, while endurance sports (running, cycling, rowing, etc) use oxidative pathways, which require more oxygen to keep energy levels for longer periods.

IMT is clearly an ergogenic agent in non-aquatic sports, by helping to reduce fatigue and energy expenditure in respiratory muscles. Thus IMT should be introduced in training routines to get an extra advantage and improve performance. Improvements were found in athletes when exercising respiratory muscles twice daily, and at least three times per week.

Don´t forget to train your respiratory muscles, they can be your secret weapon to improve your personal best.



Respiratory muscle training as an ergogenic aid.

AK McConnell

J Exerc Sci Fit, Vol 7, No 2 (Suppl), S18–S27, 2009


Inspiratory flow resistive loading improves respiratory muscle function and endurance capacity in recreational runners.

TD Mickleborough, T Nichols, MR Lindley, K Chatham, AA. Ionescu

Scand J Med Sci Sports 2010: 20: 458–468


Recent advancements in our understanding of the ergogenic effect of respiratory muscle training in healthy humans: A systematic review.

R Shei

The Journal of Strength and Conditioning Research, August 2018


The effects of inspiratory muscle training with linear workload devices on the sports performance and cardiopulmonary function of athletes: A systematic review and meta-analysis.

M Karsten, GS Ribeiro, MS Esquivel, DL Matte

Physical Therapy in Sport 34 (2018) 92e104

Human respiratory system
Device for Inspiratory Muscle Training Plus+ . (Courtesy of POWERbreathe Spain)

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