Running Physiology Explained: The Science Every Runner Needs to Know About Energy, Adaptation, and Injury

The Science of Running Training: Benefits, Risks, and Performance Optimization

Running has surged in popularity over the past decade, with millions of enthusiasts participating in challenging events worldwide. Beyond the personal achievement of crossing the finish line, there's a fascinating science behind how running training affects our bodies—from cellular energy systems to organ function and biomechanics.

Whether you're a seasoned runner or contemplating your first race, understanding the physiological adaptations, potential benefits, and risks of running training can help you train smarter and perform better while protecting your long-term health.

Running training triggers wide-ranging adaptations across the cardiovascular, musculoskeletal, endocrine, renal, immune, and respiratory systems. It enhances VO₂ max, lactate threshold, and running economy—key drivers of endurance performance. However, it also presents risks such as acute kidney injury, immune suppression, and musculoskeletal injuries. Scientific evidence supports integrating sprint interval training and periodization for optimal results. Cross-training modalities like Hyrox may further enhance fitness while reducing injury risk. Smart programming, personalized recovery, and evidence-based strategies are essential for performance optimization and long-term health in runners.

In this comprehensive guide, we'll explore the latest scientific research on running training and performance, drawing from multiple peer-reviewed studies to give you evidence-based insights into how your body responds to and adapts with endurance training.

The Energy Systems Powering Your Running Performance

ATP: Your Body's Cellular Batteries

At the most fundamental level, every stride you take during running training is powered by adenosine triphosphate (ATP)—the universal energy currency of your cells. Your body has limited ATP stores, enough for only a few seconds of intense activity, which is why you need energy systems that continuously replenish ATP during your runs.

The Three Energy Systems

Running relies on three primary energy systems, each playing different roles depending on your running intensity:

• Phosphagen System: Provides immediate energy for very short, explosive efforts (first few seconds of a sprint)

• Glycolytic System: Produces energy without oxygen (anaerobic) for high-intensity efforts lasting up to about 2 minutes

• Aerobic System: Uses oxygen to produce sustained energy for longer efforts—the primary system powering running.

Aerobic vs. Anaerobic Metabolism: Understanding the Difference

Anaerobic metabolism occurs without oxygen and produces energy quickly but inefficiently. It generates lactate as a byproduct and can only sustain effort for short periods before fatigue sets in. This system dominates during high-intensity intervals or hill sprints.

Aerobic metabolism, on the other hand, requires oxygen to produce energy and is much more efficient. It can use both carbohydrates and fats as fuel sources and is the predominant energy system during running. The better developed your aerobic system, the more efficiently you can run at your desired pace.

Key Physiological Determinants of Running Performance

VO2 Max: Your Aerobic Ceiling

VO2 max represents the maximum amount of oxygen your body can utilize during intense exercise and is considered the gold standard measurement of cardiovascular fitness and aerobic power.

Research suggests that genetics accounts for 40-50% of your VO2 max, but training can improve it by 10-20%, which can translate to significant performance gains. Higher VO2 max values correlate with better endurance performance, though it's not the only factor that determines running success.

Lactate Threshold: Your Sustainable Intensity

Your lactate threshold represents the intensity at which lactate begins to accumulate in your bloodstream faster than it can be cleared. This threshold is crucial for running performance as it effectively determines the pace you can sustain over long distances.

The good news is that lactate threshold is highly trainable—more so than VO2 max—and improvements here directly translate to faster running times. Tempo runs and threshold intervals at 80-90% of maximum heart rate are particularly effective for raising your lactate threshold.

Running Economy: Your Efficiency Factor

Running economy refers to how efficiently you use oxygen at a given pace—similar to fuel economy in a car. Two runners with identical VO2 max values can have significantly different running performances due to differences in running economy.

Several factors influence running economy:

• Biomechanics and running form

• Muscle fiber composition

• Neuromuscular coordination

• Tendon elasticity

• Body weight and composition

• Mental factors such as perceived effort

Improving running economy requires a multifaceted approach including proper strength training, technique drills, consistent running volume, and sometimes specialized methods like altitude training for elite athletes.

Recent Research on Running Training's Effects on Body Systems

Cardiovascular System Benefits and Risks

A comprehensive review published recently examined how running training affects various organ systems. The findings indicate that running training offers significant benefits for cardiovascular health, including:

• Improved cardiovascular risk factors

• Favorable cardiac adaptations

• Reduced all-cause mortality

However, the review also noted that immediately after a run, there are temporary changes in biomarkers that might suggest pathological events in the cardiovascular system. These changes typically normalize within a week, but they highlight the acute stress a run places on the heart.

In rare cases, running can pose risks such as sudden cardiac death, although such events are extremely uncommon considering the millions of runners each year.

Renal System Response

The study revealed that while running training can enhance quality of life in chronic kidney disease patients, acute kidney injury is relatively common among runners. Electrolyte imbalances, particularly hyponatremia (low sodium levels), can also occur during runs, especially when runners drink excessive amounts of water without adequate electrolyte replacement.

Gastrointestinal System Effects

Running training enhances gastrointestinal mobility and may reduce the risk of specific cancers such as colorectal cancer. However, many runners experience gastrointestinal distress during or after long-distance running, including symptoms like nausea, vomiting, abdominal cramps, and diarrhea. Proper nutrition strategies and gut training can help mitigate these issues.

Musculoskeletal Adaptations and Injuries

Running training strengthens bones and enhances skeletal muscle metabolism. However, running-related musculoskeletal injuries are common among runners, with studies showing annual injury rates between 37-56% among regular runners.

A recent cross-sectional study of 250 runners aged 15-75 years without history of running injuries provided valuable insights into biomechanical parameters across different age groups. The study found that runners over 55 years had slightly slower velocity and cadence compared to younger runners. Interestingly, natural interlimb mechanical asymmetry was high across all age groups, especially in kinetic parameters, suggesting that some level of asymmetry may be normal in healthy runners.

Immune System Response

Running is typically accompanied by an acute inflammatory response with transient immunosuppression, potentially making runners more susceptible to infections, particularly upper respiratory tract infections. This phenomenon is sometimes called the "open window" period of increased susceptibility to infection.

The review also noted that running training enhances hematopoiesis (blood cell formation) and improves the cytotoxic abilities of natural killer cells, suggesting potential long-term immune benefits despite the acute post-race suppression.

Respiratory System Changes

While running training generally enhances lung function over time, acute decreases in lung function have been observed immediately after runs. These changes typically resolve within days as the respiratory system recovers from the prolonged stress.

Endocrine System Adaptations

Hormonal alterations such as increased cortisol levels and decreased testosterone levels are commonly observed immediately after a run. Additionally, disturbances in sleep patterns are frequently reported by runners leading up to or directly after races, which can further affect hormonal balance.

Innovative Training Approaches: Sprint Interval Training vs. Traditional Training

A recent study comparing sprint interval training (SIT) versus traditional long-distance training in well-trained male distance runners yielded interesting results for those looking to optimize their training methods.

Twenty male distance runners with impressive credentials (VO2max: 67.4 ± 4.5 mL/kg/min, 5000m PB: 14'38") were divided into two groups:

• Intervention Training (IT) group performing sprint interval training

• Control Training (CT) group engaging in traditional long-distance training

Both groups completed their respective training regimens twice weekly for 6 weeks. The findings revealed that the sprint interval training group showed significant improvements in:

• Time to exhaustion

• Running performance across various distances (100m, 400m, and 3000m)

In contrast, the traditional training group only improved in 400m time. This suggests that incorporating sprint interval training into running preparation could yield superior benefits for enhancing running performance, particularly in time to exhaustion and middle-to-long distance events.

Hyrox: A New Fitness Modality for Runners

For runners looking to diversify their training, Hyrox—a fitness competition combining 8 functional exercises with running—presents an interesting option. A first-of-its-kind scientific study on Hyrox examined acute physiological responses during a simulated competition.

The study found that most of the Hyrox competition was performed at very hard and hard intensities (79.5% and 19.6% of maximum heart rate, respectively). Interestingly, faster Hyrox completion correlated significantly with:

• Higher VO2max

• Greater endurance training volume

• Lower body fat percentage

These findings suggest that Hyrox could be a suitable cross-training activity for runners, emphasizing endurance capacity with moderate requirements for strength, coordination, and mobility compared to other high-intensity functional training formats.

Practical Training Strategies for Running Success

Establish a Solid Aerobic Base

Before focusing on speed work or race-specific training, build a strong aerobic foundation through consistent easy and moderate-paced running. This develops mitochondrial density and capillary networks that enhance your aerobic capacity.

Progressive Overload

Gradually increase your training volume before ramping up intensity. Most coaches recommend increasing weekly mileage by no more than 10% to reduce injury risk while continuously challenging your body to adapt.

Targeted Workouts for Specific Adaptations

Different workouts stimulate different physiological adaptations:

• Tempo Runs: 20-40 minutes at a "comfortably hard" pace (approximately marathon pace to half-marathon pace) to improve lactate threshold

• Interval Training: Repeated high-intensity efforts with recovery periods to improve VO2 max (e.g., 5-8 × 800m at 5K pace with 2-3 minutes recovery)

• Long Runs: Weekly runs of progressively increasing distance (up to 20-22 miles for marathon training) to improve metabolic efficiency and fat utilization

Periodization

Cycle between different training emphases to optimize adaptations while preventing overtraining:

• Base Phase: Focus on building aerobic capacity and running volume

• Strength Phase: Incorporate hills and strength training

• Speed Phase: Add more high-intensity workouts

• Peak/Taper Phase: Reduce volume while maintaining intensity to arrive at the marathon fresh but fit

Complementary Training

• Strength Work: Focus on running-specific movements like squats, lunges, and hip strengthening exercises

• Flexibility and Mobility: Regular stretching and mobility work to maintain proper range of motion

• Cross-Training: Low-impact activities like cycling or swimming for active recovery days

Managing Risks: Practical Strategies

Based on the research findings regarding potential risks, here are strategies to minimize negative effects:

• Hydration: Follow a personalized hydration strategy based on sweat rate, avoiding both dehydration and overhydration

• Kidney Protection: Ensure adequate hydration without excessive water intake, and consider sodium supplementation during the race

• Gastrointestinal Comfort: Train your gut by practicing your race-day nutrition strategy during training; avoid new foods before or during the race

• Immune Support: Plan for extra rest and good nutrition in the weeks before and after a run to minimize the immunosuppressive effects

• Injury Prevention: Incorporate strength training, proper warm-up/cool-down routines, and recovery strategies to reduce musculoskeletal injury risk

• Cardiac Health: Consider a medical check-up before beginning running training, especially if you have risk factors or are over 40

FAQs About Running Training and Performance

It's fascinating how many factors influence the simple act of running! Here's a breakdown of the answers to those questions:

Q: Where does the body move when running?

Overall Movement:

• Running involves the entire body, with a primary focus on forward propulsion.

• The body's center of mass shifts vertically and horizontally with each stride.

• There's also rotational movement, particularly in the hips and shoulders, for balance and efficiency.

Key Body Part Movements:

• Legs: The legs cycle through a stance phase (foot on the ground) and a swing phase (foot in the air), involving complex movements of the hip, knee, and ankle joints.

• Arms: The arms swing in opposition to the legs, contributing to balance and momentum.

• Torso: The core muscles stabilize the torso, while the spine undergoes slight rotation.

Q: Why do runners with different body sizes run differently?

Biomechanics:

• Body size affects leverage and inertia. Taller runners may have longer strides, while shorter runners may have higher stride frequencies.

• Weight distribution influences the forces exerted on joints. Heavier runners may experience greater impact forces.

• Leg length, and the ratio of limb lengths affect the running economy of a runner.

Physiological Factors:

• Muscle mass and composition vary with body size, affecting power output and endurance.

• Lung capacity and cardiovascular function can also differ, influencing running efficiency.

Q: Does running change your body?

Musculoskeletal Changes:

• Running can increase muscle tone and strength, particularly in the legs and core.

• It can also improve bone density, contributing to skeletal health.

Cardiovascular Changes:

• Running strengthens the heart and improves circulation.

• It can also lead to a decrease in resting heart rate.

Body Composition:

• Running can help reduce body fat and contribute to weight loss.

Q: Why is running a good exercise?

Cardiovascular Health:

• It strengthens the heart and improves circulation.

Weight Management:

• It burns calories and can help with weight loss or maintenance.

Mental Health:

• It can reduce stress, improve mood, and enhance cognitive function.

Overall Fitness:

• It improves endurance, strength, and flexibility.

Q: How are running movements parametrised?

Spatiotemporal Parameters:

• These include stride length, stride frequency, stance time, and flight time.

Kinematic Parameters:

• These describe the motion of body segments, such as joint angles and velocities.

Kinetic Parameters:

• These describe the forces involved in running, such as ground reaction forces.

Biomechanical Analysis:

• Technology like motion capture, force plates, and wearable sensors are used to measure and analyze these parameters.

Researchers use these parameters to study running efficiency, injury prevention, and performance optimization.

Key Takeaways

• Running training offers comprehensive health benefits across multiple organ systems, with benefits generally outweighing risks.

• Three key physiological factors determine running performance: VO2 max, lactate threshold, and running economy—each requiring specific training approaches.

• Sprint interval training may offer superior benefits for enhancing running performance compared to traditional training alone.

• Post-run physiological changes in various organ systems typically normalize within 1-7 days.

• Common running-related issues include acute kidney injury, gastrointestinal distress, running-related injuries, and temporary immune suppression.

• Natural biomechanical asymmetry can be quite high even in healthy runners, particularly in kinetic parameters.

• Periodized training with targeted workouts for specific adaptations optimizes running preparation.

• Cross-training modalities like Hyrox can complement running training by emphasizing endurance capacity while adding elements of functional fitness.

Call to Action

Ready to elevate your running training with science-backed strategies? Start by assessing your current training approach against the evidence-based principles outlined in this article.

• Evaluate your training balance: Are you incorporating the right mix of easy runs, tempo efforts, intervals, and long runs to target all physiological systems?

• Schedule a performance assessment: Consider getting your VO2 max, lactate threshold, or running economy tested to identify your specific strengths and limitations.

• Experiment with sprint interval training: Based on the research findings, try adding one sprint interval session per week to your routine and monitor your progress.

• Prioritize recovery: Implement proper recovery strategies after intense training sessions, including nutrition, sleep, and active recovery.

• Consider cross-training: Explore complementary activities like Hyrox to enhance your overall fitness while reducing injury risk.

Remember, running training is a journey of continuous learning and adaptation. By aligning your training approach with scientific principles while listening to your body's feedback, you'll optimize both your performance and enjoyment of this challenging yet rewarding endurance pursuit.

What aspect of running training will you focus on improving first?

Related Article

Endurance Training and Body Transformation: Metabolic, Muscular, and Cardiovascular Changes Explained | Healthnewstrend

Citations

Braschler, L., Nikolaidis, P. T., Thuany, M., Chlíbková, D., Rosemann, T., Weiss, K., Wilhelm, M., & Knechtle, B. (2025). Physiology and Pathophysiology of Marathon Running: A narrative Review. Sports Medicine - Open, 11(1), 1-67. https://doi.org/10.1186/s40798-025-00810-3

Vincent, H. K., Popp, R., Cicilioni, O., Vincent, K. R., Pezzullo, L., Martenson, M., & Nixon, P. Reference Biomechanical Parameters and Natural Asymmetry Among Runners Across the Age Spectrum Without History of Running-Related Injury. Frontiers in Sports and Active Living, 7, 1560756. https://doi.org/10.3389/fspor.2025.1560756

Brandt, T., Ebel, C., Lebahn, C., & Schmidt, A. (2025). Acute physiological responses and performance determinants in Hyrox© – a new running-focused high intensity functional fitness trend. Frontiers in Physiology, 16, 1519240. https://doi.org/10.3389/fphys.2025.1519240

Jin, K., Cai, M., Zhang, Y., Wu, B., & Yang, Y. (2025). Effects of 6-week sprint interval training compared to traditional training on the running performance of distance runners: A randomized controlled trail. Frontiers in Physiology, 16, 1536287. https://doi.org/10.3389/fphys.2025.1536287

Disclaimer

The information on this website is for informational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition or treatment.Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

About the Author:

Dr.T.S. Didwal, MD, is an experienced Internal Medicine Physician with over 30 years of practice. Specializing in internal medicine, he is dedicated to promoting wellness, preventive health, and fitness as core components of patient care. Dr. Didwal’s approach emphasizes the importance of proactive health management, encouraging patients to adopt healthy lifestyles, focus on fitness, and prioritize preventive measures. His expertise includes early detection and treatment of diseases, with a particular focus on preventing chronic conditions before they develop. Through personalized care, he helps patients understand the importance of regular health screenings, proper nutrition, exercise, and stress management in maintaining overall well-being.