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Take Home Points on Swimming and Building Muscle

  1. It is believed three mechanisms exist for muscle growth (mechanical tension, metabolic stress, and muscular damage).
  2. These three mechanisms influence one another.
  3. The importance of muscle growth for swimmers is likely individual.


The importance of muscle in any sport is obvious, as muscle and strength typically


coincide. Now, swimming is a unique sport where muscles clearly don’t correspond with speed and even strength doesn’t correlate with performance. Nonetheless, understanding the main mechanisms for muscle growth are necessary, as building specific-swimming strength is necessary and muscle growth is an adaptive process for any sport.

Brad Schoenfeld and Bret Contreras have been discussing these topics in great detail, so if you want more information, please see the related reading below for further reading. This article will outline the three mechanisms for muscle growth and provide some insight on this importance for swimmers.

Many realize gaining strength, in swimming, or any avenue requires overloading the muscle with added tension on the muscle. This is believed to force muscles to grow, adapting to the stress. Unfortunately, tension is only one method for size gains, as if it were the only method power lifters would be the biggest athletes (Contreras 2013).

Although tension is commonly sought as the main mechanism of muscle growth, it is likely only one of three mechanisms:

  1. Mechanical tension
  2. Metabolic stress
  3. Muscle damage


Mechanical Tension

Mechanical tension is typically described as muscle feeling like it is going to rip off the

bone. Different types of tension do exist:

“[i]f you place tension on a muscle by stretching it passively (without letting it contract), the source of tension is called passive elastic tension. If you place tension on a muscle by flexing it as hard as possible via an isometric contraction, the source of tension is known as active tension (Contreras 2013)”.Performing a movement through the full range of motion (like in swimming or any sport) and you’ll have a combination of active and passive tension. In swimming, the mechanical tension is relatively low, but the overall volume is high (even in lower volume programs). This combination of low intensity, but high volume likely results in moderate mechanical tension.


Metabolic Stress

Imagine performing 10 x 100 for time on 2:00. Think of the feeling of your arms, as bricks

and your stomach turning … this is metabolic stress. This is a frequent feeling for swimmers, likely being the main contributor to muscle growth in the sport. Metabolic stress is aided by (Contreras 2013):

  1. The occlusion of veins by persistent muscle contractions, which prevents blood from escaping (Blood-Flow Resistance Training).
  2. Hypoxia or lack of oxygen supply in the muscles (quite common in swimming due to the lack of breathing).
  3. Build-up of metabolic byproducts such as lactate and the increased hormone surge.
  4. Cell swelling or “pump” of the muscles, also due to pooling of blood (not as common in swimmers)

Metabolic stress is likely high in swimming, due to the hypoxic nature in combination of lactate sets. 


Muscular Damage

Delayed onset muscle soreness (DOMS) typically peaks 48 hours after exercise. This damage is believed to occur from eccentric exercise or stretching a muscle while it’s being activated. Muscle damage is also spiked by exercise novelty, one reason why one is more sore at the beginning of the season or when they do a new dry-land activity. Novelty is important for building muscle size, a uncommon process in swimming, but possible through various drills and toys used in the pool. 



These three mechanisms are interrelated, as they signal hypertrophic responses through similar pathways. For example, it is uncommon to perform only one of these items. If you are performing the 10 x 100 sprints, then you’ll have high metabolic stress, accompanied with low (but still present) muscular damage, and tension. If this activity were novel (first week at practice), then the amount of damage will undoubtedly increase, making it a more anabolic activity. 

Even more interestingly, metabolic stress, places tension inside the myocytes (muscle cells), by increasing the swelling in the cell. These three mechanisms increase satellite cells (muscle stem cells) activation as well as activation of the mTOR pathway.



Now, many know elite swimmers without muscle mass. This is because swimming is a highly skilled sport, where the neural and biomechanical skills are the greatest contributor for force production. Often times, neural components are not anabolic, allowing improvements with minimal muscle growth. These items are often a continual process for those seeking improvement (even ultra-elite swimmers). In fact, one could argue ideal biomechanics are never achieved by any swimmer, and their true potential (or ceiling) is never reached. However, if you are seeking methods for increasing your ceiling (the ceiling can increase, without one increasing their force generating capacity, which likely occurs during swimming), then increasing muscle mass may increase the ceiling. This is likely most beneficial for sprint events (25- and 50-m), but may expand to 100-yard races due to the frequency of turns. If you are seeking increased muscle mass, increasing variety, and variable rep ranges/intensity are necessary for maximizing growth.

Muscles don’t just respond to tension. They respond to tension, metabolic stress, and damage. A sweet-spot of these factors likely exists that maximizes hypertrophy, and the ideal combination might differ between individuals (Contreras 2013).


Related Reading:




By Dr. G. John Mullen received his Doctorate in Physical Therapy from the University of Southern California and a Bachelor of Science of Health from Purdue University where he swam collegiately. He is the founder of Mullen Physical Therapy, the Center of Optimal Restoration, head strength coach at Santa Clara Swim Club, creator of the Swimmer’s Shoulder System, and chief editor of the Swimming Science Research Review.

Dr. John Mullen, DPT, CSCS world-renowned physical therapist and strength coach.
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