Inspiratory Muscle Fatigue in Swimmers

The goal of elite swimmers is to improve race performance and race times to achieve competitive success. The differences between winning and losing are small. Training has traditionally focused on building skeletal muscle strength and endurance; recently the focus has recently shifted to training the inspiratory musculature.

What Causes Inspiratory Muscle Fatigue in Swimming

Swimming is unique as it requires frequent breath holding, breathing patterns, and high expiration.

During races, breathing patterns play a major role in inspiratory muscle fatigue. One study suggested that breathing less frequently causes more IMF than breathing more frequently (one breath taken every fourth stroke instead of every second stroke). However, research has been unable to support a relationship between breathing frequency and IMF (inspiratory muscle fatigue). 

In a Swimming ScienceInterview, Dr. Mitch Lomax, leading inspriatory fatigue researcher, noted:

"It is important not to ignore the relationship between breathing frequency, stroke rate and stroke length here. All three can change in the presence of IMF and we have found relationships between IMF and stroke rate, and IMF and stroke length. If IMF is shortening stroke length and stroke rate is increasing to compensate, breathing frequency will also increase because breathing is coordinated with stroke cycle, especially during front crawl."

The best we can say at present is that the magnitude of IMF is not affected by breathing frequency when swimmers take a breath no less frequently than once every third stroke during a competitive 200m swim. Clearly, more work is needed to understand the interactions between IMF, breathing frequency, stroke rate and stroke length.

Focusing just on breathing frequency is likely to be too simplistic."

These thoughts by Lomax are supported by the literature, as inspiratory muscle fatigue occurs in all strokes in a similar degree. 

Research on Inspiratory Fatigue in Swimming

Lomax, notes inspiratory fatigue before racing impairs performance. Lomax later demonstrated that inspiratory muscle fatigue only negatively influences the latissimus dorsi muscles in arms only sprint swimming, not the pectoralis major.

Overall, it seems clear IMF prior to swimming impairs performance, but can inspiratory muscle training (IMT) improve swimming and prevent fatigue?

Research on Inspiratory Muscle Training and Swimming Performance

Several studies have demonstrated that training the inspiratory muscle system using an inspiratory muscle training regime (IMT) has additional benefits. IMT has been shown to enhance exercise performance in untrained and trained individuals in several endurance sports as well as during repeated sprinting.

The effect of IMT in competitive swimmers has been assessed previously. One study found that supplemental respiratory muscle training with 12 weeks of concurrent inspiratory and expiratory muscle training improved dynamic pulmonary function variables including forced inspiratory volume in 1 s (FIV1) and forced expiratory volume in 1 s (FEV1).

There was no additional improvement above that of swim training alone on ventilatory response to hypercapnia, pulmonary function, sustainable breathing power or swimming performance. The study concluded that swimming training itself may well act as a form of IMT.

A recent study from Kilding’s group assessed the role of 6 weeks of IMT in a sham controlled trial of 16 competitive club-level swimmers. The IMT consisted of 30 repetitions, twice per day using a hand-held pressure threshold device. The IMT group had a small improvement in swim times over 100 and 200 m with larger effects for maximal inspiratory pressure and rates of perceived exertion when compared to the sham control group.

Overall, the effects of IMT on performance is not well understand as the research is mixed. 

Are there any ways coaches can measure IMF without high tech equipment? 

One difficulty with IMF is measurement.

Currently, specialized equipment is needed for measurement and if you want to track improvements, like is common with other forms of training, this is difficult.

Nevertheless, IMF it is typically associated with an increase in the unpleasant sensation of breathing as well as an increase in breathing frequency and stroke rate. A word of warning here though, stroke rate and breathing frequency naturally increase with swimming speed independently of IMF. So an increase in stroke rate and breathing frequency should not automatically be taken as proof of IMF, even if swimmers are finding breathing unpleasant. IMF should be confirmed by a more direct measure and I would say that investing in a mouth pressure meter of some sort is worthwhile.

How to Improve Inspiratory Muscle Strength

Luckily, if you are looking for IMT, there are methods to strengthen the inspiratory muscle. Dr. Lomax says:

"It is clear that swim training alone is not sufficient to protect against IMF. Targeted training of these muscles is my advice i.e. inspiratory muscle training (IMT). There are various devices that can be purchased to train the breathing muscles, some are relatively inexpensive and others more so. These devices target either the inspiratory muscles or permit both the inspiratory and expiratory muscles to be trained (expiratory muscle fatigue is less frequently reported in the scientific literature but there is evidence that it too can negatively impact exercise).

There are also different types of respiratory muscle training e.g. pressure threshold training, flow resistive training and voluntary isocapnic hyperpnoea. Regardless of the type used, IMT is easy to incorporate into a training programme and can be undertaken by swimmers at home or could be integrated into a training session by a coach – typically the kit used is light and most devices are hand held. The type of IMT we administer (pressure threshold training) takes about 5 minutes to complete twice a day and consists of 30 breaths with a force equivalent to ~50% of maximum.

We have seen that inspiratory muscle strength improves in as little as four to six weeks with such a programme, and so too does performance. However, the benefits appear to plateau after around six weeks and begin fade entirely after a few months if IMT is stopped. We are currently investigating how to incorporate IMT into a swimming training programme for long term benefits i.e. IMT periodization."

Summary

Overall, it seems more research is needed on IMF and IMT before everyone jumps on board, especially if you're a casual swimmer. Just keep an eye out on the literature or if you have the time/money, consider trying IMT!

References

  1. Lomax M, Tasker L, Bostanci O. Inspiratory muscle fatigue affects latissimus dorsi but not pectoralis major activity during arms only front crawl sprinting. J Strength Cond Res. 2014 Jan 7. [Epub ahead of print]
  2. Lomax ME, McConnell AK. Inspiratory muscle fatigue in swimmers after a single 200 m swim. J Sports Sci. 2003 Aug;21(8):659-64.
  3. Lomax M, Iggleden C, Tourell A, Castle S, Honey J. Inspiratory muscle fatigue after race-paced swimming is not restricted to the front crawl stroke. J Strength Cond Res. 2012 Oct;26(10):2729-33.
  4. Lomax M, Castle S. Inspiratory muscle fatigue significantly affects breathing frequency, stroke rate, and stroke length during 200-m front-crawl swimming. J Strength Cond Res. 2011 Oct;25(10):2691-5. doi: 10.1519/JSC.0b013e318207ead8.
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Mullen, Gary. "Inspiratory Muscle Fatigue in Swimmers." ThoughtCo, Jan. 7, 2015, thoughtco.com/inspiratory-muscle-fatigue-in-swimmers-3170073. Mullen, Gary. (2015, January 7). Inspiratory Muscle Fatigue in Swimmers. Retrieved from https://www.thoughtco.com/inspiratory-muscle-fatigue-in-swimmers-3170073 Mullen, Gary. "Inspiratory Muscle Fatigue in Swimmers." ThoughtCo. https://www.thoughtco.com/inspiratory-muscle-fatigue-in-swimmers-3170073 (accessed October 18, 2017).