The Anti-Cancer Mechanisms of Aerobic Training: Research on Exercise-Induced Tumor Microenvironment Changes

Epidemiology has long shown that regular exercisers have a lower risk of cancer and higher cancer survival rates. In recent years, mechanistic studies have revealed how exercise combats cancer through changes in the immune system, hormones, and the tumor microenvironment, bringing “exercise as anti-cancer therapy” into the realm of precision medicine.

This article, grounded in research from leading international academic journals, systematically dissects the scientific basis of aerobic exercise and cancer prevention. Starting from the methods and findings of key papers, we will delve into the underlying physiological mechanisms, quantify the relationship between training dose and effect, compare differences across populations, and ultimately translate these academic findings into actionable training recommendations for Taiwanese endurance athletes. This is not merely a compilation of knowledge, but a practical map leading from the laboratory to the training ground. In an era where it is difficult to distinguish truth from falsehood, returning to rigorous scientific evidence is the most worthwhile investment for any athlete who takes their training seriously.

Review of Academic Research

The most effective way to understand this topic is to directly examine representative studies from leading international journals. Below is a compilation of several landmark or methodologically rigorous papers that, from different angles, collectively construct our current scientific understanding.

1. Moore et al. (2016, JAMA Intern Med)

This study examined exercise and cancer risk. Regular exercise reduced the risk of 13 types of cancer. The value of this study lies in its systematic approach to testing hypotheses, providing a quantifiable basis for subsequent training prescriptions and allowing us to move beyond the ambiguity of rule-of-thumb practices.

2. Hojman et al. (2018, Cell Metab)

This study provided a comprehensive review of the mechanisms of exercise and anti-cancer effects. Exercise suppresses tumors through NK cells and myokines. The value of this study lies in its systematic approach to testing hypotheses, providing a quantifiable basis for subsequent training prescriptions and allowing us to move beyond the ambiguity of rule-of-thumb practices.

3. Pedersen et al. (2016, Cell Metab)

This study examined exercise and NK cells. Exercise mobilizes NK cells to infiltrate tumors and inhibit growth. The value of this study lies in its systematic approach to testing hypotheses, providing a quantifiable basis for subsequent training prescriptions and allowing us to move beyond the ambiguity of rule-of-thumb practices.

4. Ashcraft et al. (2016, Cancer Res)

This study examined exercise and tumor blood flow. Exercise improves tumor perfusion and treatment response. The value of this study lies in its systematic approach to testing hypotheses, providing a quantifiable basis for subsequent training prescriptions and allowing us to move beyond the ambiguity of rule-of-thumb practices.

Looking across the above literature, a common trend emerges: contemporary exercise science increasingly emphasizes replacing intuition with objective data and rigorous experimental design. These studies echo and reinforce each other, collectively pointing to a consistent core conclusion, giving us greater confidence when formulating training strategies. The next section will delve into the physiological mechanisms behind these phenomena.

Integration of Core Findings

Exercise combats cancer through multiple mechanisms: adrenaline mobilizes natural killer (NK) cells and guides their infiltration into tumors; myokines (such as IL-6, irisin) directly regulate tumors; improved tumor blood flow enhances the effects of radiotherapy; and it reduces pro-carcinogenic environments such as insulin levels and inflammation. Epidemiology shows that regular exercise reduces the risk of 13 types of cancer.

It is worth emphasizing that these findings are not isolated laboratory numbers, but robust conclusions repeatedly validated across different populations and study designs. Precisely because of this, they can serve as the scientific cornerstone of training prescriptions. However, between “research findings” and “training application,” there lies a layer of mechanistic understanding—only by figuring out the “why” can we make correct adjustments in the face of individual differences and on-the-ground variables, rather than rigidly applying numbers. This is also the key dividing line between “an executor who follows a plan mechanically” and “an athlete who truly understands training”—the former merely replicates workouts, while the latter can flexibly adjust every training decision based on their own condition, environmental changes, and race demands, maximizing the benefit of limited time and energy.

Core Physiological Mechanisms

Behind any training adaptation, a cascade of physiological changes operates from the molecular, cellular, to organ-system levels. Understanding these mechanisms helps us judge which training methods truly address the limiting factors of performance and which merely add fatigue with limited benefit. The table below summarizes the key physiological mechanisms closely related to this topic and their functions:

Mechanism/Adaptation	Physiological Change	Effect on Performance
NK cell mobilization	Adrenaline-driven	Infiltration inhibits tumors
Myokines	IL-6/irisin	Regulate tumors
Tumor blood flow ↑	Improved perfusion	Enhances treatment response

These mechanisms do not operate independently but are interwoven and mutually influential within an overall network. For example, without a simultaneous improvement in peripheral muscle metabolic capacity, the increased oxygen delivery from central cardiovascular adaptations cannot be effectively utilized; and vice versa. This “barrel effect” reminds us that comprehensive and balanced training stimuli often lead to more lasting progress than extreme focus on a single point.

More importantly, the “timing” of these adaptations varies. Some changes (such as plasma volume expansion, neural coordination) can manifest within days to weeks, while others (such as cardiac structural remodeling, bone adaptations) require months or even years of accumulation. Understanding this temporal dimension helps us maintain reasonable expectations for training outcomes, avoiding the mistake of declaring a method ineffective before giving it sufficient time—a key reason why many people give up halfway.

Training Dose and Effect Relationship

“How much should I train?” is the most pressing question for every athlete. Exercise science answers this with the concept of “dose-response”—there is a quantifiable relationship between training variables (intensity, frequency, duration, volume) and the magnitude of adaptation, but this relationship is almost never simply linear. Understanding the shape of the dose-response curve helps us find the “sweet spot” with the highest return on investment, avoiding both undertraining and overtraining.

The table below summarizes dose recommendations and expected effects in different scenarios as a reference for practical planning:

Population/Scenario	Recommended Dose	Expected Effect
Regular aerobic exercise	Several times per week	Reduced risk
During cancer treatment	Moderate exercise	Improved prognosis
Survivors	Maintain exercise	Reduced recurrence

Several general principles can be drawn from the table. First, diminishing marginal returns: as fitness levels rise, the training stimulus required to achieve the same magnitude of improvement increases, which is why elite athletes often measure progress in “fractions of a percent.” Second, ceiling effect: beyond a certain threshold, additional training volume not only yields sharply diminishing returns but may even backfire due to fatigue accumulation. Third, individual thresholds: the minimum effective dose required to trigger adaptation differs for each person, explaining why the same workout plan yields vastly different results in different individuals.

Therefore, the smartest training strategy is not blindly pursuing “more,” but pursuing “just right”—providing sufficient stimulus to trigger adaptation, paired with adequate recovery to allow the adaptation to actually occur. Periodization is designed precisely to achieve this goal: through planned fluctuations in load, it avoids linear fatigue accumulation and allows the body to peak at critical moments.

Differences Across Populations

A recurring and undeniable theme in research on aerobic exercise and cancer prevention is “individual and population differences.” Applying the same conclusions indiscriminately to everyone is one of the most common errors in training prescription. Below, we analyze these differences from several key dimensions.

Beginners vs. Advanced Athletes: Beginners, being far from their physiological ceiling, respond significantly to almost any regular stimulus—this is the so-called “beginner’s bonus.” Highly trained athletes, however, have limited adaptive capacity and require more precise, higher-intensity, or more varied stimuli to continue progressing. This means the optimal training strategies for the two groups are fundamentally different; advanced athletes especially need to prioritize training “quality” and “specificity” rather than simply accumulating “quantity.”

Men vs. Women: In absolute values (such as absolute VO2max, muscle mass, hemoglobin concentration), men generally exceed women, primarily due to differences in body size, hormones, and body composition. However, in “relative training responses” (percentage improvements), differences between the sexes are often insignificant—women benefit fully from various types of training as well. Notably, women’s menstrual cycles, hormonal fluctuations, and energy availability (RED-S risk) need special consideration in training planning.

Age Differences: With advancing age, maximal heart rate, muscle mass, recovery speed, and hormonal environment all change, but extensive research confirms that even middle-aged and older populations retain the capacity to adapt to training, albeit potentially at a slower rate and requiring more recovery. In other words, “it’s useless to train when you’re old” is a complete myth. Older adults, in fact, need regular training even more to combat sarcopenia, bone loss, and cardiorespiratory decline.

Genetic Factors: Don’t forget the “responder–non-responder” phenomenon. Large family studies indicate that a considerable proportion of training response can be explained by genetics, meaning that faced with the same plan, some progress rapidly while others improve slowly—often not due to lack of effort, but inherent differences in response potential. Recognizing this helps athletes maintain a healthier perspective on their own and others’ progress rates and become more willing to experiment with different training modes to find the stimulus that suits them.

Practical Training Application

The value of theory lies in guiding practice. Translating research findings on aerobic exercise and cancer prevention into daily executable training requires grasping three key principles: “specificity,” “progression,” and “measurability.”

Specificity Principle: Training must target the energy systems and physiological adaptations required by the goal. If the goal is long-distance endurance, substantial aerobic base training is needed; to break through VO2max limits, targeted high-intensity interval stimuli are required. The most common problem with indiscriminate training is falling into the “moderate-intensity black hole”—each session is somewhat breathless but not hard enough, failing to effectively build the aerobic base while also not reaching the critical high-intensity stimulus, ultimately leading to stagnation.

Progression Principle: The body only adapts when faced with loads slightly above its current capacity, but load increases must be gradual. A practical guideline is to “keep weekly training volume increases within approximately 10%” and schedule a deload week every 3–4 weeks to allow accumulated fatigue to dissipate and adaptations to consolidate. Rushing progress is the number one cause of injury and overtraining in amateur athletes.

Measurability Principle: Replacing subjective feelings with objective data is the core of modern training. It is recommended to establish the following monitoring habits:

• Morning resting heart rate and heart rate variability (HRV): Reflect recovery status and autonomic nervous system balance; an abnormally elevated resting heart rate or a sudden drop in HRV is a warning sign of fatigue.
• Power or pace: Tracking output at the same intensity under standardized conditions is the most objective way to assess fitness progress.
• Subjective fatigue and sleep quality: Simple daily self-assessments capture overall status beyond the numbers.
• Periodic testing: Conduct a standardized test (such as threshold power, time trial) every 6–12 weeks to objectively evaluate training effectiveness and adjust accordingly.

Integrating these principles, a mature training plan should be “building the base with large volumes of low intensity, pushing the ceiling with small volumes of high intensity, consolidating adaptations with adequate recovery, and navigating direction with objective data.” Rather than blindly chasing mileage numbers every day, it is better to execute 1–2 high-quality sessions per week with discipline and truly relax the rest of the time—this is the essence of quality over quantity.

Local Application in Taiwan

Cancer has long been the leading cause of death in Taiwan, making exercise for cancer prevention and adjunctive therapy highly significant. Aerobic activities such as cycling and brisk walking are accessible and easy to perform. It is recommended that the general population exercise regularly to reduce risk, and that cancer patients, under the guidance of their medical team, engage in moderate exercise to improve treatment tolerance and quality of life.

Taiwan’s unique geographical and climatic conditions necessitate local adaptation when applying conclusions from international research. The hot, humid summers, mountainous terrain, and dense, diverse race culture are both challenges and advantages. By knowing how to utilize high-altitude resources like Hehuan Mountain and Wuling for altitude stimulus, how to perform heat acclimatization and maintain hydration and electrolyte balance in hot, humid environments, and how to adjust training focus based on the characteristics of Taiwanese races (such as a high proportion of climbing), Taiwanese endurance athletes can turn local conditions into a competitive advantage. Remember, any data from laboratories in temperate countries needs to be interpreted and applied against Taiwan’s actual training environment—this is the final mile for scientific training to take root locally.

Debunking Common Myths

There is often a significant gap between scientific findings and popular beliefs. Many “common sense” notions widely circulated in the sports community do not withstand empirical scrutiny. Below, we debunk common myths related to this topic one by one:

Myth 1: Exercise has nothing to do with cancer.

In reality, exercise reduces the risk of multiple cancers and improves prognosis. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

Myth 2: When sick, you should rest completely.

In reality, moderate exercise aids treatment and recovery. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

Myth 3: Only prevention is useful.

In reality, exercise during treatment and survivorship is equally beneficial. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

The key to debunking myths lies in cultivating the habit of “asking for evidence.” Whenever you hear any training claim, ask yourself, “What research supports this? Which population does it apply to?” Only by relying on evidence can we avoid plausible-sounding traps in the age of information overload and make truly beneficial training decisions.

Conclusion: From Evidence to Action

Looking across the academic research on aerobic exercise and cancer prevention, several clear conclusions emerge. First, endurance performance is the result of the synergistic action of multiple physiological systems; no single metric or training method holds the exclusive key to success. Second, the essence of training is “precise stress plus adequate recovery,” not merely the accumulation of effort. Third, individual differences are omnipresent; the best training plan is always the one “tailored for yourself and continuously adjusted based on data.”

Looking ahead, exercise science is rapidly advancing toward “precise individualization.” Advances in genomics, metabolomics, and wearable devices will eventually allow us to predict an individual’s response potential before training and fine-tune each session in real time based on physiological data. For Taiwanese athletes and coaches, building a local physiological database and developing training models adapted to the local climate and races are crucial tasks for narrowing the gap with the world’s elite.

For every reader, the most important action recommendation remains the same: First, understand your physiological baseline through objective testing; then design training based on scientific principles; pair it with disciplined recovery and continuous monitoring; and be patient with progress. There are no shortcuts to building endurance, but there is a correct direction. May this science-based analysis serve as a reliable guide on your training journey, accompanying you in pursuing your limits while also enjoying the purest joy of sport.

Related Reading

• The Impact of Aerobic Training on Telomere Length: Molecular Biology Research on the Anti-Aging Mechanisms of Exercise
• The Benefits of Exercise in Cancer Adjunctive Therapy: Research on Safe Training During Chemotherapy
• Exercise Intervention After Female Breast Cancer: Research on the Benefits of Aerobic Training During Chemotherapy
• The Benefits of Long-Term Aerobic Training on Cognitive Function: Research on Hippocampal Volume and BDNF