When we think of terrifying opponents in combat sports, we often picture someone muscular with broad shoulders, perhaps a fast-twitch fighter who packs dynamite in his hands, capable of ending a fight with a single clean punch.

I beg to differ. The most terrifying archetype in fighting is the relentless and unbreakable pressure fighter. What makes this type so terrifying is their ability to take punishment while constantly moving forward, never giving their opponent time to breathe or reset. No matter how many shots they absorb, they keep coming—like a zombie—the walking dead. These fighters have accepted their mortality; they are prepared to die in the ring; they are dead and alive at the same time.

You could be the greatest tactician, but if you’re up against a freak like this, with unnatural physical and psychological endurance and seemingly a granite chin, you’d better finish the fight, or you’re in for a tough night.

We could say (with a little exaggeration) that this type of fighter tests an opponent’s will more than their technique or tactics. Every second feels like survival, and soon, even the most skilled boxer can crumble under the psychological pressure of an unbreakable force who simply won’t stop. This relentless pace forces mistakes, drains energy, and turns the fight into a war of attrition.

I hereby present you with perhaps the greatest freak athlete in recent history: Oleksandr Khyzhniak.

Being an expectation to the rule

In any sport, there are principles shaped by years of refinement and passed down through generations. In boxing, one of these principles is to assume unpredictability—hiding your intentions. And for good reason: the goal is to hit without getting hit.

Expect… Some fighters don’t rely on unpredictability; in fact, everyone knows exactly what they’re going to do. But it doesn’t matter—because the real question is, can their opponent handle it? When talking about fighters like Khyzhniak with an inhumane gas tank and resilience, the only way is to either match their pace or end the fight quickly. Khyzhniak understands this and embraces his predictability with no hesitation. For him, it just doesn’t matter, because he knows that most of his opponents will not have an answer anyway. They might match his p  ace or even outwork him for the first minute or an entire round, but very rarely will they be able to match it for the entire fight—eventually, they will crumble and succumb to the inevitable fatigue.

The pressure a fighter like this applies is terrifying to face in the ring. If you’re not moving, he’s hitting you. If he’s hitting you, he doesn’t stop. It’s a relentless blizzard while you desperately seek shelter.

Establishing your brand

As cliché as this might sound, all of us have a unique genetic make-up that is further shaped by all of the experiences we have gone through—both physically and personality-wise. There has never been and never will be an exact genetic copy of you—you’re a one-time deal. We are all predisposed to certain attributes and traits.

Some athletes have gas tanks for days, others are twitchy and explosive, and others are in between. The key lies in identifying what category you belong to and, above all, knowing your psychological strengths and limitations.

To be fair, this is a very sensitive and multifaceted territory, so I am very careful when drawing strong conclusions and voicing my opinions. This is by no means an attempt to quantify them. But on a general basis, perhaps we can all agree on this: people are different, each possessing unique cognitive and physical strengths and weaknesses that are influenced by both genetic predisposition and environmental factors.

Some athletes rank highly in mental and cognitive attributes such as competitiveness and resilience, while others prefer to take a more tentative or picky approach, and some may feel anxiety and pressure more than others. Yet, despite these differences, they may all, under the right circumstances, be capable of reaching world-class standards. There is no single-deciding attribute—it’s all an intricate clockwork. Ultimately, it comes down to the individual athlete, and shaping a plan brings out one’s greatest attributes.

It is such a simple concept that is needlessly overcomplicated—why choose a path that is inappropriate for your innate strengths? If you ‘naturally’ excel at X, why would you choose Y? If you naturally outran all of your teammates in the 100-meter field, you should pursue sprinting, not marathon. If you effortlessly jump 40 inches without any prior training, you should perhaps choose a sport that can make use of this quality. If you’re a snappy and twitchy boxer who packs dynamite, chances are (although not necessarily) that you will lack other attributes, such as stamina. Choose a strategy that paves the way for this.

Some fighters have a trademark—something they do better than others—a moat that is hard to break through, acquired from years of trial, error, and introspection.

When speaking of these moats, we may think of Mayweather’s ability to slip punches with his shoulder roll, Tyson’s combination of explosive power and the peek-a-boo defensive style, Lomachenko’s footwork and his ability to create angles and step around opponents, and, of course, Khyzhniak’s relentless forward pressure and inhuman endurance.  

Obviously, it’s not all physical attributes; Khyzhniak is a master of inside fighting. This is his world. He’s been doing this for years, day in and day out, in every boxing practice session. He has found this to be the department at which he excels, and above all, he is a master at taking the fight to that department exactly—nullifying any advantage his opponent may have over him. He goes full terminator mode, sticking to his objective, wastes no time, and doesn’t fool around. This is a timeless principle of combat sports: take the fight where you are the strongest and the opponent is the weakest.

He is not reckless, as some might think. In fact, he is a defensive genius for the style he has adopted (the very reason his aggressive forward-moving style works in the first place is due to his defense). Some may notice him crossing his feet at times during a match and interpret it as ‘unrefined,’ but they are missing the context. While this is not something a beginner boxer should be taught, in Khyzhniak’s case (as an inside fighter), his primary objective is to fight on the inside as quickly as possible. Sometimes, to achieve that, he may naturally cross his legs to accelerate forward rather than maintaining a traditional stance. Once inside, he has an incredibly tight and compact guard, and his opponents very rarely land a clean shot on him. He absorbs the majority of his shots on the guard. In this regard, his fundamentals are exceptionally well developed. For an outside observer, it might look chaotic and ugly, but there is tremendous technical finesse to his game.

Additionally, he implements a form of ‘’catch and pitch’’ style as explained by Teddy Atlas. Which involves catching or deflecting an incoming punch. (Atlas uses the analogy of catching a ball to explain the action of receiving a punch). After blocking, Khyzhniak uses the inertia of the block to quickly follow up with a counterpunch, taking advantage of the opening. Essentially, the opponent’s attack and your counterpunch combine into a single, harmonious movement. This method is particularly useful when fighters are in close proximity, where traditional long-range punches may not be as effective. It involves keeping the body close to the opponent, utilizing short and powerful punches, and remaining compact like a package. It can be seen as a way to turn a defensive move into an offensive opportunity.

Muscle fiber types

The body’s skeletal muscles are made up of different types of fibers with varying characteristics. Some are twitchy and explosive, while others are slower and more durable, and these fibers may change size or composition depending on the demand placed upon them. In regards to this variance, sports scientists have developed a classification system.

This classification is determined by firing rate and fatigue resistance; as a result, they are classified as slow-twitch and fast-twitch muscle fibers. The fast-twitch fibers are further divided into two types: Type IIa and Type IIx (the latter being the more powerful but more susceptible to fatigue).

Slow-twitch fibers primarily rely on aerobic metabolism, whereas fast-twitch fibers rely on anaerobic metabolism; thus, the former are more common in talented endurance athletes such as long-distance runners and cross-country skiers, whereas the latter (Types IIa and IIx) are more prevalent in power athletes such as sprinters, weightlifters, and throwers.^1,2 (Luckily, boxing has no optimal proportion of muscle fiber types because the sport is so diverse—your proportion will likely dictate the style you adopt.)

If we were to dissect a muscle, we would find morphological variance in the fibers, with the more powerful fiber types being whiter in color and the slower and more endurant types being more densely red due to the high levels of myoglobin and capillaries.³

There are advantages and disadvantages to each type. Slow-twitch muscle fibers fire at a slower rate, but they are better able to supply energy and withstand fatigue over time. Fast-twitch fibers, on the other hand, produce a high power output but fatigue quickly, mainly due to their high ATPase activity (the enzyme responsible for the breakdown of ATP).^2,4

It should also be noted that advances in histochemical techniques have led to even further classifications in subcategories of muscle types, i.e., hybrid muscle fibers such as I/IIa and IIa/IIx.² Those hybrid muscle fibers will range from slow twitch to fast twitch, leaning predominantly towards one or the other. Thus, when it comes to classification, there appears to be a gray zone.

Muscle Fiber Type	Contraction Speed	Fatigue Resistance	Force Production	Energy Source	Color
Type I (Slow Twitch)	Slow	High	Low	Aerobic (oxidative)	Red
Type IIa (Fast Twitch)	Fast	Low	High	Anaerobic (glycolytic)	White
Type IIx (Fast Twitch)	Very Fast	Very Low	Very High	Anaerobic (glycolytic)	White

Genetics of muscle fibers

A study conducted on North American men and women revealed significant variability in the proportion of Type I muscle fibers in the vastus lateralis muscle, ranging from 35 to 65%.¹⁹

This gives insight into how certain athletes may have an innate predisposition for certain athletic attributes. For example, whether one is fast and twitchy but easily fatigued, whether one is slow and durable, or somewhere in between.

This begs the question: are they elite because of their muscle fiber composition, or have their training regimens over time shaped this distribution? If the latter, to what extent did training influence the outcome?

Nature and nurture meet again. We know they both matter, but to what extent is another issue. In Khyzhniak’s case, he is likely in the mid-pint, a predominance of Type IIa fibers, further backed by a tremendous amount of endurance training, controlled pacing, and mental clarity (stay tuned).

Defining fatigue

To understand endurance, we must first understand fatigue. What is fatigue, and what causes it? In athletic contexts, it can simply be described as a bodily response that increases one’s desire to cease the activity due to discomfort. This discomfort is primarily caused by the release of various byproducts into the bloodstream, including lactate and hydrogen ions from anaerobic metabolism, as well as the depletion of energy sources like glycogen or creatine. Such fatigue can be classified as ‘physical’ or peripheral (for the fancy scientific term).

A lesser-known type of fatigue is that of the brain (the central nervous system)—known as central fatigue. As the name implies, you simply feel tired in your brain. The brain, like the muscles, becomes fatigued after a long period of intensively recruiting motor units.

Undoubtedly, central fatigue is an enormous area with numerous contributing factors. Biochemical aspects (e.g., serotonin levels), emotional aspects (e.g., anxiety or anger), environmental aspects (e.g., an optimistic or pessimistic environment), the list goes on.

In essence, peripheral fatigue is the tiredness and subsequent decline in muscle performance following exercise, whereas CNS fatigue is the decline in the CNS’s ability to activate muscles.^21,22

Regardless of the type of fatigue we’re discussing, the two main deciding factors are the athlete’s fitness and experience. A more physically fit and experienced athlete will recover more quickly, be less aroused and anxious in various situations, and reduce the severity of both peripheral and central fatigue.

Defining endurance

Endurance is sometimes misnamed ‘cardio.’ This term is an abbreviation for ‘cardiovascular’, which refers to the relationship between the heart and blood vessels. When the heart pumps, oxygen flows to the muscles via the blood vessels, resulting in aerobic metabolism.

However, if we define endurance as the ability to delay the onset of fatigue and endure it when it occurs, there are more factors to consider. These include anaerobic metabolism, neuromuscular factors, and psychological factors. When we define endurance in this way, it opens up a whole new set of parameters. As the figure below depicts, these include: aerobic capacity and power, neuromuscular factors, and psychological factors. These can then be broken down into smaller subcomponents:

All of the above contribute to higher movement efficiency, lactate threshold, VO₂max, power output, and mental toughness—resulting in increased endurance. And each of these broad categories has a suitable training method.^13,23

Common methods for increasing aerobic capacity include steady-state endurance and lengthy interval training. Various HIIT formats primarily target anaerobic factors and lactate threshold (with a secondary focus on aerobic endurance). Strength and power training is best suited for neuromuscular factors such as motor unit recruitment and rate coding, as well as the powerful ATP-PCr system. Refining your technique (on the training modality in question) will improve your motor control and movement efficiency.

Regarding the psychological aspects of endurance, we can all agree that mental toughness plays a crucial role. However, defining this and its origins is a bit more complex, which would require a separate book.

As you can see, when endurance is viewed from this perspective, it becomes multifaceted. Now it’s more than just running a 5K or doing some intervals here and there. It becomes like clockwork, with all training interventions influencing each other.

One could argue that this complicates the process, but simplifying at the expense of accuracy is not a viable solution either. With enough knowledge, you can at least focus your efforts in the right direction.

Importance of relaxation for endurance

When most people think of endurance, what typically comes to mind are the biochemical aspects, such as having a high VO₂max, a high lactate threshold, etc. However, the factors associated with mental clarity and relaxation seem to be overlooked. How is this related to endurance?

Imagine you’re backed into a corner, met with a barrage of punches from the opponent. You try to go to your left, but the opponent follows up. You go to the right, same thing. You’re trapped. A powerful shot lands on your chin; you tense up, and before you have even processed what has occurred, another shot follows up—all while you’re isolated in this corner. Naturally, most people, especially inexperienced ones, would tense up and go into fight-or-flight mode. Stress hormones such as adrenaline, noradrenaline, and cortisol are released, and the energy expenditure shoots up. Ironically, this is precisely the situation where you need to maintain the highest level of relaxation to make sound decisions. The more experienced the boxer, the better they will regulate this stress response, and the more clear-headed they can stay in overwhelming situations like this.

Therefore, to conserve energy, you must have mental clarity and remain calm under pressure. It doesn’t matter if you can run a 5K in world-class numbers—it is not the same as hand-to-hand combat. If you tense up too much in boxing, you will deplete your tank very quickly. Many athletes, while objectively possessing good endurance in terms of physiological attributes, suffer from significant energy leaks in terms of movement efficiency and relaxation. It is often less of an energetic question than a mental/psychological one.

Conversely, imagine you’re the aggressor (as Khyzhniak so often happens to be), with a fighting style that delivers endless combinations and forward pressure. Although it may appear that he is very tense in there, trying to end his opponent with every shot, he is actually very relaxed, and he paces himself very well. He displays excellent movement economy, tensing up and relaxing at the right moments. All of this while his opponent’s fatigue skyrockets due to an overwhelming forward pressure.

I can imagine that he puts a lot of training into pacing, mindfulness, and controlled breathing. Since his style is so bound to stamina and constant pressure, he probably does everything in his capacity to aid this attribute, approaching it from every possible improvable entry point—both physically and psychologically.

One of the first conclusions that beginner boxers draw when they get tired quickly is that they lack fitness. I often get questions like, “How long should I be able to run before starting boxing?” or “What fitness level is required?” My answer is always the same: it doesn’t matter. When you first start, you’ll feel fatigued, not necessarily due to a lack of fitness but due to a lack of relaxation, poor coordination, and mental clarity. You’ll experience unnecessary tension at the wrong moments.

One fascinating study compared the performance of soccer players who were given cues to induce relaxation (such as smiling and loosening up), to a control group that played normally without any specific instructions, and another group that was encouraged to frown and tense their muscles. The results revealed that players who followed the relaxation cues had a significantly higher running economy than the other groups.²⁴

Learning to relax takes a long time to master. Even professional athletes on the world stage are working on it using techniques like visualization, affirmations, and mindfulness.¹⁵

If there is one takeaway from this section, it’s that your mental and physical relaxation will significantly affect your endurance. It is especially important to remain calm and composed during critical situations. It is counterintuitive because we have a natural tendency to become tense as the situation gets more critical. This is clearly not a skill that one is born with; it requires training.¹⁶ A pilot or astronaut has years of training to remain calm and mentally clear in critical situations. If a screw came loose on a spaceship, it’s not the time for irrational emotions and tense reactions. In such a case, a far better solution would be to enter cold-hearted inspector mode and solve the problem objectively. It’s not about suppressing emotions or avoiding anxiety; the key is to master them instead of allowing them to control you. Use them to your advantage, which is entirely possible with proper training.

Sources

1. Pette, D., Peuker, H., & Staron, R. S. (1999). The impact of biochemical methods for single muscle fibre analysis. Acta Physiologica Scandinavica, 166(4), 261-277.
2. Scott, W., Stevens, J., & Binder-Macleod, S. A. (2001). Human skeletal muscle fiber type classifications. Physical Therapy, 81(11), 1810-1816.
3. McComas, A. J. (1996). Skeletal muscle, form and function. Human Kinetics.
4. Haff, G. G., & Triplett, N. T. (Eds.). (2015). Essentials of strength training and conditioning (4th ed.). Human Kinetics.
5. Pette, D., & Staron, R. S. (1997). Mammalian skeletal muscle fiber type transitions. International Review of Cytology, 170, 143-223.
6. Ricoy, J. R., Encinas, A. R., Cabello, A., Madero, S., & Arenas, J. (1998). Histochemical study of the vastus lateralis muscle fibre types of athletes. Journal of Physiology and Biochemistry, 54(1), 41-47.
7. Plotkin, D. L., Roberts, M. D., Haun, C. T., & Schoenfeld, B. J. (2021). Muscle fiber type transitions with exercise training: Shifting perspectives. Sports, 9(9), 127.
8. Malisoux, L., Francaux, M., Nielens, H., & Theisen, D. (2006). Stretch-shortening cycle exercises: An effective training paradigm to enhance power output of human single muscle fibers. Journal of Applied Physiology, 100(3), 771-779. Andersen, J. L.,
9. Klitgaard, H., & Saltin, B. (1994). Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: Influence of training. Acta Physiologica Scandinavica, 151(2), 135-142.
10. Bathgate, K. E., Bagley, J. R., Jo, E., Talmadge, R. J., Tobias, I. S., Brown, L. E., & Galpin, A. J. (2018). Muscle health and performance in monozygotic twins with 30 years of discordant exercise habits. European Journal of Applied Physiology, 118, 2097-2110. 11.
11. Howald, H., Hoppeler, H., Claassen, H., Mathieu, O., & Straub, R. (1985). Influences of endurance training on the ultrastructural composition of the different muscle fiber types in humans. Pflügers Archiv, 403(4), 369-376.
12. Trappe, S., Harber, M., Creer, A., Gallagher, P., Slivka, D., Minchev, K., & Whitsett, D. (2006). Single muscle fiber adaptations with marathon training. Journal of Applied Physiology, 223 101(3), 721-727. Strength and Conditioning for Wrestling.
13. Zatsiorsky, V. M., Kraemer, W. J., & Fry, A. C. (2020). Science and practice of strength training (2nd ed.). Human Kinetics.
14. Burnham, R., Martin, T., Stein, R., Bell, G., MacLean, I., & Steadward, R. (1997). Skeletal muscle fibre type transformation following spinal cord injury. Spinal Cord, 35(2), 86-91.
15. Biering-Sørensen, B., Kristensen, I. B., Kjær, M., & Biering-Sørensen, F. (2009). Muscle after spinal cord injury. Muscle & Nerve, 40(4), 499-519.
16. Scott, W., Stevens, J., & Binder-Macleod, S. A. (2001). Human skeletal muscle fiber type classifications. Physical Therapy, 81(11), 1810-1816.
17. Vikne, H., Strøm, V., Pripp, A. H., & Gjøvaag, T. (2020). Human skeletal muscle fiber type percentage and area after reduced muscle use: A systematic review and meta analysis. Scandinavian Journal of Medicine & Science in Sports, 30(8), 1298-1317.
18. Andersen, L. L., Andersen, J. L., Magnusson, S. P., Suetta, C., Madsen, J. L., Christensen, L. R., & Aagaard, P. (2005). Changes in the human muscle force-velocity relationship in response to resistance training and subsequent detraining. Journal of Applied Physiology, 99(1), 87-94.
19. Simoneau, J. A., & Bouchard, C. (1989). Human variation in skeletal muscle fiber-type proportion and enzyme activities. The American Journal of Physiology, 257(4), E567-E572.
20. Andersen, J. L., Schjerling, P., & Saltin, B. (2000). Muscle, genes, and athletic performance. Scientific American, 283(3), 48-55.
21. Davis, J. M. (1995). Central and peripheral factors in fatigue. Journal of sports sciences, 13(S1), S49-S53.
22. Tornero-Aguilera, J. F., Jimenez-Morcillo, J., Rubio-Zarapuz, A., & Clemente-Suárez, V. J. (2022). Central and peripheral fatigue in physical exercise explained: A narrative review. International journal of environmental research and public health, 19(7), 3909.
23. Bompa, T. O., & Buzzichelli, C. (2019). Periodization-: theory and methodology of training. Human kinetics.
24. Brick, N. E., McElhinney, M. J., & Metcalfe, R. S. (2018). The effects of facial expression and relaxation cues on movement economy, physiological, and perceptual responses during running. Psychology of Sport and Exercise, 34, 20-28.