Special Forces: Ultraendurance and the Immune System

SPECIAL FORCES: ULTRAENDURANCE AND THE IMMUNE SYSTEM

Ricardo Guerra is an exercise physiologist who works
with professional soccer teams and other elite personnel.
He has a Master of Science in sports physiology from Liverpool John Moores University.
Most recently, he provided consultation to elements within the Italian police infrastructure.

28 April 2025
DefesaNet

DefesaNet Note

English version of a previous text published in Portuguese

Forças Especiais: Ultrarresistência e Imunologia

The Editor

SPECIAL FORCES: ULTRAENDURANCE AND THE IMMUNE SYSTEM

In recent years, there has been a notable surge in various modalities related to endurance competitions, including marathons, triathlons, and Ironman triathlons. Many athletes engage in rigorous training regimens to adequately prepare for race days. Some take these competitions so seriously that they travel extensively and make significant personal sacrifices. Often, juggling the demands of work, family, and a strict training schedule can become an overwhelming challenge. Yet, most athletes are convinced they reap substantial health benefits from their involvement in these sports.

Interestingly, the trend is not limited to amateur athletes. Elite units within the Armed Forces around the globe place a high premium on conditioning, particularly regarding aerobic capacity. It would be hard to find a member of the Navy SEAL teams—the United States Navy’s most renowned special operations force—who does not possess exceptional aerobic fitness. Many warriors participate in ultra-endurance competitions to prepare for their demanding roles. They would likely do very well in marathon and triathlon competitions if they were not fully committed to their units.

There’s a common perception that most forms of physical activity contribute positively to health, general well-being, and self-esteem, often overlooking the training load involved. This viewpoint, however, is overly simplistic and, at times, grossly generalized. It may be time to delve deeper into the practice of sports and physical activities that bring us such joy and satisfaction. Certainly, the psychological and physiological benefits of regular exercise are well-established, with numerous studies highlighting that moderate physical activity can enhance our immune systems, boost brain function, and even reduce the risks of cardiovascular disease and certain cancers.

But what if participating in these prolonged ultra-endurance events doesn’t provide the benefits that many athletes hope for? What if the intense training—sometimes recommended by those lacking formal qualifications in Exercise Physiology or Physical Education—not only threatens family and work life, but gradually undermines immune function? Extreme physical exertion can, at some point, do more harm than good and might even pose health risks. Many professional and amateur athletes are often unaware of the potential damage they inflict on their bodies. All too frequently, thousands across the globe, influenced by a network of trainers and self-proclaimed experts, find themselves subjected to excruciating training methods with excessive loads that can gradually weaken their immune systems.

Our immune system continually encounters challenges from various pathogens. Its robustness and effectiveness hinge on several factors, including genetic predispositions, environmental conditions, stress levels, diet, sleep quality, aging, and the amount of physical activity we engage in. Moreover, harmful habits such as drug addiction and indiscriminate use of certain medications, tobacco, and alcohol can erode immune resistance. Overusing antibiotics can disrupt the microbiome, resulting in lengthy recovery periods for this essential system and consequently affecting immune function.

Athletes frequently experience upper respiratory infections, such as colds, sore throats, and sinusitis in the days and weeks following significant races. This phenomenon is well-documented in scientific literature. Studies indicate that the likelihood of contracting upper respiratory infections can skyrocket by two to six times in the weeks following participation in a marathon or ultramarathon. Reports also link flu-like symptoms to periods of excessive training.

It’s worth noting that Special Forces units maintain physical standards that emphasize endurance and require covering extensive distances on foot with heavy loads. In the final stages of training for entry into Delta Force, candidates must complete approximately 50 miles while carrying a backpack weighing at least 70 pounds in under 17 hours.

Moving through such painful distances of mountainous terrain with an additional 70 pounds of diverse cargo on your backpack over a pre-determined amount of time is an unsurmountable task for the vast majority of people. It is infinitely more arduous and complex than simply carrying your weight under the same conditions. That in itself is already an extraordinary physical feat. Now imagine what these special forces operators can execute. Unique capabilities physiologically and psychologically empower a Delta Force or Navy Seal operator. These attributes are simply awe-inspiring.

Both ultra-endurance athletes and Special Forces members have elite levels of aerobic capacity. However, Special Forces members also have a high degree of overall core and functional muscular strength. This systemic type of muscular strength is biomechanically in unison. Most elite and ordinary long-distance runners don’t even come close to this specific capability compared to special forces members.

Special forces operatives not only have remarkable physical abilities but also possess unique cognitive processes and perspectives that enable them to view issues from unconventional angles. Such neurological capacity gives them insights and ideas many people might struggle to develop. They are capable of navigating through the most unexpected challenges and situations. This mind-boggling blend of mental and physical prowess empowers them to achieve extraordinary accomplishments that most civilians cannot match.

Parallel to that, some of the most intense periods of Special Forces training are often linked to severe sleep deprivation, strenuous exercise, and extreme reduction of psychological reserves, which together depress various immune parameters, leading to greater vulnerability to respiratory infections. It is not uncommon, for example, for Navy Seal candidates to succumb to double pneumonia and other related illnesses during these intense and unconventional training/testing phases.

Some physiologists and researchers advocate that prolonged exercise becomes harmful and that various immune system components begin to be affected after intense, continuous running lasting more than 90 minutes. And yet, a marathon can involve more than five hours of constant exercise, and an Ironman can last up to 17 hours.

The immune suppression that follows prolonged exercise is associated with increased levels of stress hormones, particularly adrenaline and cortisol, which rise during physical activity. High concentrations of these hormones can decrease essential blood cells, notably white blood cells like neutrophils and lymphocytes, which are crucial for a strong immune system. Neutrophils, in particular, can be likened to the iconic Pac-Man from the 1980s video game, tirelessly devouring harmful microorganisms in our bodies. Consequently, when the levels of these immune cells drop, our vulnerability to infections rises. In addition, excessive and prolonged exercise can disrupt other complex immune defense mechanisms.

Fortunately, the decline in immune function following an ultra-endurance race is reversible for most individuals. However, the challenge dedicated athletes face is not just the physical strain endured during competitions like marathons or Ironman events but also the ongoing compromise of their immune systems due to intense training regimens leading up to race day. As a result, their physical and psychological well-being may be constantly under pressure.

One might visualize the immune system taking repeated hits during weekly training sessions, ultimately leading to a “knockout” on race day. It’s worth considering the potential long-term effects on the immune system for those who regularly participate in several marathons a year while adhering to excessive training programs that lack a scientific foundation in exercise physiology.

This gradual, relentless weakening of the immune system over several decades could make someone more prone to serious health issues down the line. I often recall an enlightening conversation I had years ago at a sports medicine conference. I spoke with the medical director of a prominent ultra-endurance event. When I inquired about the long-term effects of yearly participation in these types of events coupled with intense training, he told me that several competitors he had observed over the years had unexpectedly developed different forms of cancer. I asked if he had any data to support his observations, but he noted that his conclusions were based solely on anecdotal accounts.

Regular, excessive exercise triggers the production and release of pro-inflammatory cytokines, which can disrupt various biological systems and mechanisms. When exercise is overly intense or lasts too long, and if there’s not enough time for rest, the body might struggle to handle the inflammation effectively. This phenomenon can, in turn, lead to chronic inflammation. Finding an exercise load that promotes beneficial immune adaptations is essential, though what constitutes the “ideal” amount can be somewhat subjective. Many physiologists recommend that moderate physical activity, like brisk walking or jogging for about 45 minutes five days a week, promotes health, overall well-being, and the physiological changes that bolster the immune system. This ideal activity level falls far short of the stress and exertion in marathons, Ironman races, or other ultra-endurance events.

Understanding how exercise impacts the immune system is crucial. This knowledge can deepen our appreciation for Exercise Physiology and the invaluable resources it offers to ultra-endurance athletes and Special Forces members. Exercise physiologists’ various techniques to accelerate recovery are significant for those engaged in ultra-endurance tasks.

Restoring glycogen levels within 36 hours following a marathon is achievable if athletes adhere to a suitable diet, utilize the right ergogenic supplements, and allow for adequate recovery time. One can draw an analogy between how glycogen operates in our muscle cells and the gasoline in a car’s tank—glycogen is the fuel that powers muscle contractions.

Beyond glycogen replenishment, other strategies, including various ergogenic supplements, are vital for restoring and enhancing our body’s defenses. These approaches can help minimize stressors to the immune system. Additionally, strengthening, stimulating, and diversifying the microbiome is essential to fostering and maintaining robust immunity. Over the years, researchers have increasingly recognized the microbiome’s significant role in influencing and integrating various physiological systems.

An exercise physiologist can leverage specific, advanced resources to enhance and sustain an individual’s physiological capacity. The effectiveness of these strategies depends on the athlete’s discipline in adhering to the recommended schedules for consuming various substances throughout the day. This commitment is key. Other modalities outside of the nutritional umbrella can also be utilized to augment recovery processes.

Certainly, in the context of Special Forces, undertaking extreme training loads can be crucial for achieving specific strategic goals. And some people will likely always be motivated to engage in endurance related modalities. Yet, activities such as running for four hours or more, spending prolonged hours swimming in the water, or cycling—similar to what Ironman competitors do—should not be considered exercise loads that enhance the immune system.

Towards the later part of his esteemed career, Dr. Kenneth Cooper cautioned that there comes a moment when excessive exercise can result in diminishing returns, ultimately undermining individuals’ immune systems.

On the other hand, the psychological and physiological benefits of daily physical activity are well-documented. And thus, a more moderate exercise routine is likely far more beneficial to everyone in the long run.

Ricardo Guerra is an exercise physiologist who works with professional soccer teams and other elite personnel. He has a Master of Science in sports physiology from Liverpool John Moores University.

Most recently, he provided consultation to elements within the Italian police infrastructure.

Throughout his career, Ricardo has worked with numerous football clubs across the Middle East and Europe, including serving the national teams of Egypt and Qatar. In 2015, he took on the role of exercise physiologist for Olympique de Marseille during their run to the French Cup final against PSG.

Ricardo holds the highest coaching license from The Football Association (England) and a UEFA license. He has traveled extensively worldwide, collecting data and evaluating the physiological capacity of soccer players from various countries.

For years, he has been consulting with some of the most elite athletes in the strongman modalities and refining those methodologies for practical purposes.

The author is a Ph.D. candidate and the author of an upcoming book about Brazilian soccer.

His articles have been published in over five languages across multiple news organizations.

He can be contacted at [email protected]

Other articles from Professor Ricardo Guerra in Portuguese

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