Physiology of the Extreme: Survival Mechanisms in Limit-Pushing Sports

March 27, 2025

From ultramarathons under a scorching sun to freediving at dozens of meters below the surface, more and more athletes are taking on extreme challenges that test the limits of human capability.
These feats demonstrate that the human body can adapt even to the most hostile environments. But how does one reach such a level of endurance?
What adaptive mechanisms help us survive—and sometimes even excel—in environments we usually consider inhospitable to life?

Extreme Sports: Physiological Stress and Biological Plasticity

The key to understanding these performances lies in the extraordinary plasticity of the human organism.

When subjected to extreme but controlled stress, the body can trigger adaptive processes involving the cardiovascular, muscular, respiratory, metabolic, and neuroendocrine systems.

During a desert ultramarathon, for instance, the body must operate in a constant state of energy depletion, with ambient temperatures exceeding 45°C.

The body activates a range of adaptive responses: it increases sweating, improves thermoregulation efficiency, and builds greater tolerance to dehydration.

Even as fluids decrease due to dehydration, the cardiovascular system continues to deliver sufficient blood and oxygen to the tissues.

Systemic Training and Acclimatization

These changes don’t happen overnight.

They require highly specialized training protocols—often built on periodized cycles—and extended acclimatization processes.

The underlying principle is hormesis: gradual exposure to a stressor improves the body’s ability to cope with it.

In the case of deep freediving, for example, we observe phenomena like diving bradycardia, peripheral vasoconstriction, and the so-called blood shift, where blood moves toward the lungs to prevent alveolar collapse under pressure.

Athletes can further enhance these partly innate responses—shared as an evolutionary trait with marine mammals—through targeted training, breathing techniques, and exercises that build tolerance to hypercapnia and hypoxia.

A Delicate Balance

Cold environments and high altitudes present entirely different challenges.

Extreme mountaineering—such as Himalayan expeditions without supplemental oxygen—requires the body to drastically increase red blood cell production to compensate for low oxygen partial pressure.

At the same time, mitochondrial adaptations in muscle tissue improve energy production under anaerobic conditions.

In response to extreme cold, the body triggers thermogenic responses like peripheral vasoconstriction, an increase in basal metabolic rate, and, in some cases, activation of brown adipose tissue, which is specialized in heat generation.

However, the balance between maintaining core body temperature and preventing tissue damage from frostbite remains extremely delicate.

Genetics, Mindset, and Psychophysical Resilience to the Extreme

Finally, it’s important to note that not everyone responds in the same way.

Genetics plays a key role.

Some elite athletes, for instance, possess gene variants that facilitate adaptation to hypoxia, dehydration, or thermal stress.

But beyond biology, there’s a crucial—often overlooked—factor: mental resilience.

The ability to endure pain, manage anxiety, tolerate prolonged discomfort, and remain mentally clear in extreme conditions often separates those who succeed from those who don’t.

For this reason, mental training, visualization, and biofeedback techniques have become essential tools in elite performance preparation.

At the Edge of the Human, Not the Impossible

The human body can, in fact, adapt to environmental conditions that seem incompatible with survival.

This is made possible by a combination of physiological, genetic, and psychological changes.

These transformations are triggered and strengthened through specific training, acclimatization strategies, and solid mental preparation.

Confronting extreme environments is not just an athletic challenge.

It’s also an opportunity to explore the untapped potential of the human body and the adaptive capabilities that have always enabled us to survive and thrive in the world’s most hostile conditions.

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