Stamina: A Life Long Asset

Written By Jennifer Pishko

Prepared by the CrossFit Medical Society with contributions from Dr. Jeanette Watkins and Jenn Pishko, MS, Nutrition Education

Key Takeaways

  • Stamina is more than grit—it's a measurable indicator of how efficiently your body uses energy.

  • Improvements in stamina metrics reflect powerful cellular adaptations that reduce oxidative stress, improve metabolic health, and increase resilience.

  • CrossFit’s constantly varied, functional, and high-intensity workouts are uniquely effective at developing these capacities.

The Cellular Architecture of Stamina

When most athletes hear “stamina,” they picture grinding through a grueling WOD. But in the CrossFit Level 1 Training Guide, stamina is defined more precisely: “the ability of body systems to process, deliver, store, and utilize energy.” This definition reframes stamina not as sheer willpower, but as a reflection of underlying cellular efficiency, and something that can be intentionally trained and measured.

Clinically, two physiological markers provide insight into this efficiency:

  • VO₂ max is like the size of your fuel tank and the horsepower of your engine combined. It indicates the highest rate at which your body can use oxygen during intense activity. 

  • Lactate threshold (LT) is your redline– the point at which your engine starts overheating as lactate builds up faster than it can be cleared. It’s a marker of metabolic flexibility, how effectively at different intensities your body can switch between using carbs and fat for fuel, before fatigue sets in.

These measures are more than just workout stats—they’re windows into cellular and metabolic health. In a landmark 46-year study of more than 5,000 men, researchers found that every 1 mL/kg/min increase in VO₂ max translated into an extra 45 days of life. Those with the highest fitness levels lived nearly five years longer than those with the lowest [1]. Similar research in both men and women shows that each 1-MET increase in VO₂ max is tied to a 13% lower risk of death from all causes [2].

Another key marker, the lactate threshold (LT), has been linked to better physical function, greater independence, and reduced risk of frailty [3]. While LT hasn’t been studied as extensively as VO₂ max in relation to mortality, it’s one of the best predictors of how well people perform—and recover—under real-world stress [4].

CrossFit training improves both markers through its foundational methodology: constantly varied, functional movements performed at high intensity. This approach challenges the body’s ability to take in and use oxygen, boosting VO₂ max [5]. At the same time, repeated efforts near threshold levels push the “redline” higher, raising LT and delaying fatigue [6]. The result is a training model that not only builds workout capacity but also strengthens the very markers most closely tied to long-term health and longevity.

The Cellular Revolution: How CrossFit Transforms Mitochondria

At the cellular level, CrossFit-style training sets off a chain of reactions that change how your body makes and uses energy. The star of this process is mitochondrial biogenesis—the creation of new mitochondria and the improvement of the ones you already have. If mitochondria are your body’s “power plants,” then training builds more of them and upgrades each one to run more efficiently. Research shows that high-intensity exercise greatly boosts PGC-1α, the “master switch” for this process [7]. Once it’s flipped on, your cells begin large-scale remodeling: more mitochondrial DNA, stronger enzymes for energy production, and better communication between power plants. It’s like replacing an old power grid with a modern, high-capacity system.

Another key player is AMPK, the cell’s “fuel gauge” and metabolic first responder. During demanding workouts, when energy use outpaces supply, AMPK jumps into action. When energy use outpaces supply, AMPK acts like a gear shift. Your body has to up its horsepower—pulling in more glucose, burning more fat, and then activating PGC-1α to build out a bigger, more efficient energy network.The harder the workout, the stronger the AMPK signal—like pressing the gas pedal [9]. This explains why CrossFit, with its intensity and variety, is especially good at driving these cellular upgrades.

CrossFit also taps into a principle called hormesis: small doses of stress that make the body stronger. High-intensity workouts briefly increase reactive oxygen species (ROS). ROS are tiny, unstable molecules your body makes during exercise and metabolism. In small amounts, they act as signals that tell your body to adapt and get fitter (like building stamina and resilience). But if there’s too much, they can cause damage [10]. In other words, the stress from CrossFit doesn’t wear you down—it teaches your body to bounce back stronger, improving recovery, resilience, and long-term health.

CrossFit’s Practical Benefits 

CrossFit’s design uniquely stimulates widespread cellular adaptation. Where traditional training often isolates a single energy system, CrossFit’s constantly varied structure activates all three energy pathways—phosphagen, glycolytic, and oxidative—across diverse movement patterns and time domains.This variety keeps adaptation moving forward and helps avoid plateaus, while providing the perfect stress dose to boost cellular defenses without overloading the body. 

In practical terms, the results speak for themselves. In just 12 weeks, CrossFit participants have shown 9–17% strength gains, higher VO₂ peak, better fatigue resistance, and improvements in explosive power [11]. The benefits don’t stop at the physical level. A single CrossFit session can improve working memory and self-control by 12–15%, outperforming moderate-intensity exercise [12].  These outcomes all stem from the powerful cellular adaptations that CrossFit is uniquely designed to unlock.

Conclusion: An Inclusive Tool for Health

CrossFit’s focus on measurable, observable, and repeatable results makes it easy to track progress in stamina. Benchmark workouts act as checkpoints, showing athletes exactly how their endurance improves over time. Just as important, CrossFit’s use of relative intensity means workouts can be scaled for anyone—whether you’re a beginner, a seasoned competitor, young, or older. By adjusting load, reps, or complexity while preserving the workout’s intended stimulus, every athlete can build stamina effectively and safely.

These improvements aren’t just about workout scores—they reflect deep cellular upgrades: stronger and more numerous mitochondria, smarter energy regulation, and greater resilience. That’s why stamina training carries over into everyday life, supporting long-term health, independence, and overall quality of life. As CrossFit Founder Greg Glassman put it, “The needs of Olympic athletes and grandparents differ by degree, not kind.” The pursuit of stamina benefits everyone—helping athletes not only add years to their lives, but more life to their years.

Action Steps for Coaches

  • Retest benchmarks regularly: Use repeatable workouts to track stamina gains over time.

  • Scale for intent, not ease: Ensure all athletes experience the intended metabolic stimulus by adjusting load, movement, or duration based on capacity.

  • Educate your athletes: Explain how stamina connects to health, longevity, and life outside the gym to build buy-in and motivation.

References

[1] Laukkanen, J. A., Lavie, C. J., Khan, H., Kurl, S., & Kunutsor, S. K. (2019). Cardiorespiratory Fitness and the Risk of Serious Ventricular Arrhythmias: A Prospective Cohort Study. Mayo Clinic proceedings, 94(5), 833–841. https://doi.org/10.1016/j.mayocp.2018.11.027

[2] Kodama, S., Saito, K., Tanaka, S., Maki, M., Yachi, Y., Asumi, M., Sugawara, A., Totsuka, K., Shimano, H., Ohashi, Y., Yamada, N., & Sone, H. (2009). Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA, 301(19), 2024–2035. https://doi.org/10.1001/jama.2009.681 

[3] Tanaka, H., & Seals, D. R. (2008). Endurance exercise performance in Masters athletes: age-associated changes and underlying physiological mechanisms. The Journal of physiology, 586(1), 55–63. https://doi.org/10.1113/jphysiol.2007.141879 

[4] Faude, O., Kindermann, W., & Meyer, T. (2009). Lactate threshold concepts: how valid are they?. Sports medicine (Auckland, N.Z.), 39(6), 469–490. https://doi.org/10.2165/00007256-200939060-00003 

[5] Buchheit, M., & Laursen, P. B. (2013). High-intensity interval training, solutions to the programming puzzle: Part I: cardiopulmonary emphasis. Sports medicine (Auckland, N.Z.), 43(5), 313–338. https://doi.org/10.1007/s40279-013-0029-x 

[6] Gist, N. H., Freese, E. C., Ryan, T. E., & Cureton, K. J. (2015). Effects of Low-Volume, High-Intensity Whole-Body Calisthenics on Army ROTC Cadets. Military medicine, 180(5), 492–498. https://doi.org/10.7205/MILMED-D-14-00277 

[7] Abrego-Guandique, D. M., Aguilera Rojas, N. M., Chiari, A., Luciani, F., Cione, E., & Cannataro, R. (2025). The impact of exercise on mitochondrial biogenesis in skeletal muscle: A systematic review and meta-analysis of randomized trials. Biomolecular concepts, 16(1), 10.1515/bmc-2025-0055. https://doi.org/10.1515/bmc-2025-0055 

[8] Li, Y., Zhao, W., & Yang, Q. (2025). Effects of high-intensity interval training and moderate-intensity continuous training on mitochondrial dynamics in human skeletal muscle. Frontiers in physiology, 16, 1554222. https://doi.org/10.3389/fphys.2025.1554222 

[9] Jäger, S., Handschin, C., St-Pierre, J., & Spiegelman, B. M. (2007). AMP-activated protein kinase (AMPK) action in skeletal muscle via direct phosphorylation of PGC-1alpha. Proceedings of the National Academy of Sciences of the United States of America, 104(29), 12017–12022. https://doi.org/10.1073/pnas.0705070104 

[10] Niknam, A., Gaeini, A.A., Hamidvand, A. et al. High-intensity functional training modulates oxidative stress and improves physical performance in adolescent male soccer players: a randomized controlled trial. BMC Sports Sci Med Rehabil 17, 38 (2025). https://doi.org/10.1186/s13102-024-01037-7 

[11] Rios, M., Pyne, D. B., & Fernandes, R. J. (2024). The Effects of CrossFit® Practice on Physical Fitness and Overall Quality of Life. International journal of environmental research and public health, 22(1), 19. https://doi.org/10.3390/ijerph22010019 

[12] Wilke, J., Giesche, F., Klier, K., Vogt, L., Herrmann, E., & Banzer, W. (2019). Acute Effects of Resistance Exercise on Cognitive Function in Healthy Adults: A Systematic Review with Multilevel Meta-Analysis. Sports medicine (Auckland, N.Z.), 49(6), 905–916. https://doi.org/10.1007/s40279-019-01085-x 

Jennifer Pishko
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