All You Need to Know About Inspiratory Muscles Part I

No matter the distance, every swimmer is out of breath at the end of a race….excuse me if I just blew your mind! This obvious statement has lead swim coaches to attempt various training means to prevent “being out of breath” as the main limiting factor in swimming. The most common attempt was increasing swimming volume, while others implemented underwater training to improve this function, unfortunately, some swimmers will have limitations secondary to inspiratory muscle fatigue. Of the two aforementioned strategies, underwater training should improve the isometric strength of the forced inspiratory muscles, but is this enough to maximize and optimize inspiratory muscle performance…

Quiet breathing is necessary to live and it is essential for athletes (and everyone) to breathe properly at rest. At rest, the diaphragm is the primary breathing muscle and improper use of their diaphragm can cause added stress to other structures. From my experience, approximately 50% of Junior National level swimmers have improper diaphragm use and dissociation!

This series will address the breathing muscles/biomechanics, the importance of inspiratory strength, effects inspiratory fatigue demonstrates on performance, screening and lastly discuss a few dryland exercises to improve this deficiency. Let’s start improving this number and optimizing swimming potential!

Breathing Biomechanics
Breathing is a uniquely simplistically complex function performed by numerous muscles. It is commonly believed the chest is the primary location of respiration. This misconception is secondary to the location of the lungs, but when emphasized can lead to faulty breathing patterns. Before we discuss faulty patterns, let’s discuss the four types of breathing and typical biomechanics:

Quiet Inspiration
Quiet Expiration
Forced Inspiration
Forced Expiration

Here is what the John Hopkin’s School of Medicine has to say about respiration:

“During quiet breathing, the predominant muscle of respiration is the diaphragm. As it contracts, pleural pressure drops, which lowers the alveolar pressure and draws air in down the pressure gradient from mouth to alveoli. Expiration during quiet breathing is predominantly a passive phenomenon, as the respiratory muscles are relaxed and the elastic lung and chest wall return passively to their resting volume, the functional residual capacity.

However, during exercise, many other muscles become important to respiration. During inspiration, the external intercostals raise the lower ribs up and out, increasing the lateral and anteroposterior dimensions of the thorax. The scalene muscles and sternomastoid also become involved, serving to raise and push out the upper ribs and the sternum.

During active expiration, the most important muscles are those of the abdominal wall (including the rectus abdominus, internal and external obliques, and transversus abdominus), which drive intra-abdominal pressure up when they contract, and thus push up the diaphragm, raising pleural pressure, which raises alveolar pressure, which in turn drives air out. The internal intercostals assist with active expiration by pulling the ribs down and in, thus decreasing thoracic volume.”

During a deep inspiration these are the steps I look for:

Diaphragm descends
Ribs expand, elevate and rotate forward
Shoulder blades move laterally

As stated, many people feel the chest and lungs need to be the primary mover for inspiration. This is commonly due to the lack of understanding of which muscles are used during inspiration. Here’s a list of the muscles during passive breathing and inspiration:

Diaphragm: This inspiratory muscle lies across the bottom of the rib cage and is essential for optimal swimming and breathing. Is commonly felt during belly breathing and helps raise and lower the abdominal wall, allowing expansion of the lungs. Used during all forms of breathing.
Intercostal Muscles: These muscles help expand the chest and move the ribs, allowing for further chest expansion. Different fiber orientations are used during different times. External fibers are used during inspiration and internal are used during expiration. Used during all forms of breathing.
Scalenes: There are three scalene muscles which attach from the first few ribs to various vertebral structures. These muscles should only be used during inspiration (preferably forced).
Pectoralis Minor: Runs from ribs 3-5 to a part of the shoulder blade (coracoid process). Mainly used during inspiration.
Serratus Anterior: Spans from the outer surface of ribs 8 and 9 to the shoulder blade. Used during inspiration.
Sternocleidomastoid: Spans from the sternum and collarbone to the back of the head. Used during inspiration.
Levator Costarum: This muscle runs from the sides of the vertebrae to the posterior aspect of the ribs. Used during inspiration.
Upper Trapezius: Runs from the back of the head to the outside of the collarbone. Used during inspiration.
Latissmus Dorsi: Segments exist at multiple parts, most notably for breathing at the 3rd and 4th rib and shoulder blade running to the inside of the arm. Used during inspiration.
Subclavis: Runs from the first rib to the shoulder blade. Used during inspiration.

As you can see, inspiration is a complex movement utilizing many muscles. Ten muscles alone are used to breathe inward, this doesn’t include the importance of expiratory muscles (mainly the abdominal muscles). The epicenter of inspiratory breathing is the diaphragm, imagine if this muscle is not working correctly….more stress is placed on specific shoulder muscles, potentially leading to earlier fatigue in the arms and inspiratory muscle fatigue or worse, shoulder injury. Stay tuned for the next installments, focusing on the expiratory muscles, a literature on inspiratory muscle fatigue, screening, and exercises.

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