The Most Active Muscles in Freestyle Swimming

The Most Active Muscles in Freestyle Swimming

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The Most Active Muscles in Freestyle Swimming

Swimming requires heavy amounts of repetition. It’s repetitive nature demands high amounts of strength and endurance from your muscles. This is particularly evident in freestyle swimming as it is the most common swim stroke used

It is important to investigate how these muscles are used so you can properly strengthen the high-priority muscles and prevent overuse injuries. As the shoulder is the main propulsive force in swimming, most analysis and research has been performed in the upper extremities.

Fine-Needle EMG Test

In an older, yet fundamental, article by Pink et al.2, the researchers explored how the upper extremity muscles are used during freestyle swimming. They used fine-needle EMG to test when muscles were active and measured the percent of activity.

They placed fine-needles in the individual muscle bellies. They monitored the amount and duration of muscle activity for that particular muscle. The researchers also recorded the signal intensity for upper extremity muscles during moderately paced freestyle swimming. They compared that signal intensity with a manual muscle test (MMT) for the same muscle. The muscle activity was then reported as a percentage of its MMT (%MMT).

Swim Stroke Phases

The researchers also simultaneously videotaped the swimmers, allowing them to link the EMG data with the stroke cycle to see which specific muscles were being used during the specific phases of the stroke cycle.

They broke down the swim stroke into two phases: (1) the recovery phase and (2) the pull phase.

Each phase was further divided into early and late categories. Thus, the swim stroke for one arm consisted of an early pull phase, followed by a late pull phase, then an early recovery phase, followed by a late recovery phase.

While this is a rather simplistic (and outdated) view of the stroke cycle compared with today’s standards3,4, it gave the researchers a basic system to analyze the stroke cycle. In addition, the basic muscle firing patterns of the stroke remained similar to the modern stroke style, making this a reliable description of stroke firing patterns.

You’ll note that this system did not take into consideration the “catch” phase of the stroke cycle. The researchers realized this after the data was collected and made special mention of this in the article. This, however, did not change the general results of the data gathered.

The researchers analyzed the following muscles:

  • Anterior, middle, and posterior deltoid
  • Rotator Cuff Muscles – Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis
  • Rhomboids
  • Upper trapezius
  • Serratus Anterior
  • Pectoralis Major
  • Latissimus Dorsi

The authors measured when which muscles were active during the stroke cycle and at what percentage of MMT (%MMT).

Significance of the Results

I would like to hone in on one of the results from this article that I believe is most valuable for coaches and swimmers.

They found the subscapularis and serratus anterior muscles to be consistently active throughout the entire stroke cycle at levels >20%MMT. No other muscles exhibited this type of activity. They go on to reference another article by Monad et al.5, which found that muscles functioning between 15% and 20% of their maximal voluntary contraction are at the highest level of sustainable activity before fatigue sets in.

To put this in perspective, all the other muscles tested had brief periods with higher level of activity. Periods with minimal activity followed this phase, allowing the muscles to rest.

The serratus anterior and the subscapularis muscles did not have these rest periods, meaning they had to perform continually and with little to no rest.

This is quite a demand placed on these two muscle and exposes a vulnerability in the stroke cycle.

I believe this is important because it lets us know a potential place for breakdown in the stroke cycle. When a muscle fatigues, two things happen:

  • It becomes more susceptible to injury.
  • Other muscles compensate for the fatigued muscle, causing altered stroke mechanics and increased potential for injury to other muscles. It’s almost like a cascade effect that can trickle its way down to several other muscles and eventually affect the entire stroke.

Real-World Application
Knowing this, we can direct special attention to these muscles to ensure they perform at an optimal level and meet their demands. We can condition the serratus anterior muscle –during dryland practice– for endurance so that it can handle the continual load demanded of it.

We can also include serratus anterior muscle activity while exercising other muscle groups to further adapt this muscle to continual low-level loads. We can do the same for the subscapularis. This muscle, however, has a natural tendency to become too restrictive, which can affect the muscle balance of the upper extremities.

To be more specific to the subscapularis, we must include stretching and soft tissue techniques to prevent this muscle from becoming too tight or restrictive.

The important takeaway from this research is that the serratus anterior and subscapularis muscles are very important muscles in freestyle swimming. They merit swimmers’ and coaches’ continual attention via strengthening or stretching to ensure they can perform at their optimal level. We can discuss how to specifically exercise these muscles in a later article.


1.Beach ML, Whitney SL, Dickoff-Hoffman S. Relationship of shoulder flexibility, strength, and endurance to shoulder pain in competitive swimmers. J Orthop Sports Phys Ther. 1992;16:262-268.
2.Pink M, Perry J, Browne A, et al: The normal shoulder during freestyle swimming An EMG and cinematographic analysis of twelve muscles Am J Sports Med 19. 569-576, 1991
3.Johnson JN, Gauvin J, Fredericson M. Swimming biomechanics and injury prevention: new stroke techniques and medical considerations. Phys Sportsmed. 2003;31:41-46.
4.Souza TA: The shoulder in swimming, in Sports Injuries of the Shoulder: Conservative Management. New York City, Churchill Livingstone, 1994, pp 107-24
5.Monad H. Contractility of muscle during prolonged static and repetitive dynamic activity Ergonomics 28(1) 81-89, 1985wilfred diaz headshot

Written by Wilfred Diaz, P.T., D.P.T., O.C.S. Wilfred received his Bachelor of Science degree in Kinesiology from Cal Poly San Luis Obispo. He then attended the University of Southern California, receiving his Doctor of Physical Therapy degree. While at USC he received the Honor of the Golden Cane award. This is the highest honor awarded to graduates demonstrating outstanding accomplishments in a variety of professional areas. Wilfred is also a Board Certified Orthopaedic Specialist. Wilfred regularly attends courses to stay up to date on the latest treatments and research, and helps patients with most all orthopaedic diagnoses. Wilfred does treat a high amount of water athletes due to his background in water sports. Wilfred is fluently bilingual in Spanish and English.

Originally posted May 2013

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