How Marathon Training Transforms Your Body: The Science of Endurance 🏃‍♀️

With the Cape Town Marathon just around the corner, I thought it would be an apt time to delve into the amazing and complex physiological adaptations that occur when we commit to endurance training, or more specifically, a marathon training plan. We're not just getting fitter; we are scientifically remodelling our internal systems for peak performance.  

So, let’s dive into it... 

Cardiovascular Adaptations - The Optimized Pump 

The most striking change from consistent, long-duration endurance training occurs in your heart. This process, known as cardiac remodelling, is why highly trained runners have exceptionally low resting heart rates. 

The training stimulus causes a thickening of your heart walls and a significant enlargement of the left ventricle (the main pumping chamber). This adaptation allows your heart to dramatically increase its stroke volume (the volume of blood ejected with each beat).  

Since cardiac output is the product of heart rate and stroke volume, increasing stroke volume allows your heart to deliver the same, or even greater, amount of oxygenated blood to your working muscles with fewer beats or rather, a lower resting heart rate. This enhanced efficiency is a core contributor to your VO2 Max (your body's maximum capacity to use oxygen). 

Training also improves efficiency at the muscle level. Your muscles grow a massive network of tiny blood vessels called capillaries, which shortens the distance oxygen has to travel from your blood into your working cells. 

Metabolic Adaptations - Fuelling the Long Haul 

Every marathon runner knows the feeling of hitting "the wall," the sudden, dreadful moment your body runs out of its carbohydrate fuel. 

When you start running, your body's preferred fuel is stored carbohydrates, or glycogen. Glycogen is fast and easy to burn, but your body stores a very limited supply, typically only enough for about 90 minutes of intense effort. 

The key to marathon success is becoming efficient at utilizing the body’s nearly limitless reserve: fat. 

The moment your body senses those glycogen stores are running low, it executes a "fuel mobilization" plan, sending massive amounts of fat into your bloodstream to be burned for energy. This switch is made possible by the engine's powerhouses: the mitochondria. 

Endurance training causes these tiny power generators to multiply inside your cells and become much better at using oxygen and burning fuel. This fat adaptation is critical because: 

• Fat is stored in huge amounts. 

• Training allows your body to process that fat more efficiently at higher intensities, sparing your limited glycogen stores for those later, critical miles of the race. This is how you delay the wall. 

Studies confirm this mobilization, showing that markers for Free Fatty Acids (fat fuel) can jump by an incredible 5.8 times immediately after a race. 

Systemic Stress and Risk Management 

While training makes you a stronger machine, the race itself is a temporary stress test. Understanding these limits is vital for a safe, successful run. 

Intense, prolonged exertion triggers a significant, though temporary, inflammatory and stress response. High levels of stress hormones transiently suppress your immune system for about 3 to 72 hours post-effort. This creates an "open window" where you are more susceptible to picking up infections. This is precisely why it is so important to prioritize meticulous hygiene, rest, and sleep immediately after your hardest runs and the race itself. 

Blood Shunting and Internal Organs 

During the systemic stress of a marathon, blood is actively diverted away from non-essential organs to fuel your working muscles. This is called splanchnic blood shunting. While prioritizing your working leg muscles, this shunting causes trouble elsewhere: 

• Gastrointestinal issues: Reduced blood flow to the gut causes tissue ischemia (a lack of oxygen), leading to issues like nausea and the infamous "runner's trots." Takeaway: Practice your race nutrition during long runs and never experiment on race morning. 

• Kidney risk: In extreme cases, this reduced blood flow can stress your kidneys. Takeaway: Skip the NSAIDs (painkillers like ibuprofen); they can make your kidneys much more vulnerable during a long, hard race. Prioritise adequate hydration and electrolyte management during and after the race.  

Musculoskeletal Adaptations - Building a Resilient Frame 

The belief that running ruins your joints is largely a myth. Research shows that recreational runners have a lower risk of osteoarthritis (OA) than people who are sedentary. Joint tissues, bones, and cartilage actually adapt to the load and become stronger and healthier. 

However, the number one reason runners get hurt is trying to force the supporting tissues to adapt faster than they are physiologically capable: 

• Tendons and Ligaments: These structures have less blood flow and remodel their collagen much slower than muscle tissue. The common 10% Rule respects their slow adaptation rate. 

• Bone Density: Increasing mileage too quickly can cause bone breakdown to outpace bone-building, leading to stress reactions or stress fractures. 

Takeaway: Listen to persistent pain. Pain that is sharp, localized, and doesn't go away is a signal that a structure is failing to adapt. When in doubt, scale back. 

Taper Week Essentials 

You're running with a scientifically optimized machine. The key to longevity in this sport is respecting the science of adaptation - push the engine hard enough to change, but never so hard that the frame breaks. 

Here are a few practical things to prioritize as you prepare for the race: 

• Taper like you love yourself. The last 7–14 days are for backing off mileage so your legs arrive fresh. You don't "lose fitness" - you just let fatigue go. 

• Sleep. Aim for more, not less. 

• Carbs on race week. Increase them sensibly to top up your glycogen tanks. 

• Hydration. Practice your fluid and electrolyte strategy, avoiding excessive plain water consumption. 

• Skip the NSAIDs. Use ice or rest for niggles; painkillers increase kidney risk during the race. 

I wish everyone running the Cape Town Marathon all the very best! 

Run strong and healthy,  

Dr. Megan Males, 

General Practitioner 

The Science of Endurance