How to Build Mileage As a Runner: A Physiological Perspective

Running, like any physical endeavor, is fundamentally governed by the laws of physiology. If you want to build mileage as a runner, it's essential to understand how your body responds to the demands of increased distance. Let's explore this from a physiological perspective and delve into strategies that optimize your body's adaptation for long-distance running.

1. Aerobic Capacity:

Distance running is primarily an aerobic activity, which means your body relies on oxygen to produce energy. When you increase mileage, you're essentially challenging your aerobic capacity. Over time, your heart becomes more efficient at pumping blood, and your muscles develop a higher number of mitochondria (the powerhouses of your cells). This allows your muscles to produce a greater amount of ATP (Adenosine Triphosphate) in a shorter amount of time and therefore, improving your endurance.

2. Slow and Steady Increases:

The physiological process of building mileage is intrinsically tied to the concept of progressive overload. Gradual, incremental increases in distance allow your body to adapt without excessive stress. Sudden jumps in mileage can lead to injuries and limit physiological adaptations. It's all about striking the right balance between challenging your body and allowing it to recover. **One golden rule of running is to never increase weekly mileage and intensity at the same time!

3. Muscular Adaptations:

Distance running places specific demands on your leg muscles. When you build mileage, your muscles undergo various adaptations. Your slow-twitch muscle fibers become more efficient at utilizing oxygen, mostly from building capillary networks throughout the muscle fibers for easy oxygen exchange and more mitochondria, allowing you to sustain a steady pace for longer. Additionally, connective tissues, such as tendons and ligaments, strengthen to support the increased workload. **All this takes time, so do not rush the process. If you get injured it will take you significantly longer to successfully improve your mileage.

4. Energy Systems:

Your body utilizes different energy systems during running. Short sprints rely on the anaerobic system (phosphagen system and anaerobic glycolysis), while longer distances primarily engage the aerobic system. Building mileage shifts your body's preference toward the aerobic system, which can sustain energy production over extended periods from 2 minutes up to 24+ hours. This transition is crucial for endurance running (also in sprinters a lot more than you would think). **Your training runs need to focus on aerobic system, which means the run should feel easy! If it doesn’t than you will never improve your mileage because you are training the wrong energy system.

5. Thermoregulation:

As you increase mileage, your body's ability to manage heat becomes more efficient. Sweating and cooling mechanisms improve, helping you maintain a stable core temperature. This is especially important during long, hot runs to prevent heat-related issues.

6. Fuel Utilization:

Your body becomes better at using stored energy sources, such as glycogen and fat, as you build mileage. Efficient fuel utilization is key to preventing the dreaded "wall" in long-distance running. Your body learns to conserve glycogen and switch to fat as a primary energy source, extending your endurance.

7. Heart and Lung Function:

Distance running significantly enhances cardiovascular function. Your heart becomes stronger, pumping more blood with each beat (stroke volume), and your body’s ability to use oxygen improves (VO2 Max). **Your lung capacity doesn’t change, but your bodies ability to utilize the full extent of your current lungs capacity does improve with endurance training. Most people do not reach the full potential that their lungs have to offer, because they don’t train aerobic system enough.

8. Recovery and Overtraining:

Understanding your body's recovery limits is critical. Overtraining can lead to physiological setbacks, such as suppressed immune function, hormonal imbalances, and increased injury risk. Balancing training with adequate rest and nutrition is vital for avoiding overtraining. **Injuries from overtraining are caused because your body is underprepared for the stress you put on it. If you have an adequate stress/rest ratio, especially with a running coach/physical therapist, then you will likely never obtain an overuse/overtraining injury.

9. Individual Variability:

It's important to remember that physiological responses to training can vary from person to person. Genetics, age, and previous running experience play a role in how your body adapts to increased mileage. Therefore, it's crucial to tailor your training to your individual needs and capabilities. **I always recommend runners to discuss their goals with a trained running specialist or a performance physical therapist to design a training program specifically with the goals in mind!

In conclusion, building mileage as a runner is a remarkable journey of physiological adaptation. By understanding how your body responds to the increasing demands of distance running and applying the principles of progressive overload, and challenging the correct energy systems, you can optimize your training and reach your long-distance running goals while minimizing the risk of injury and maximizing your performance potential. May the information of physiology be your ally on the road to success!

If you have any questions, feel free to reach out via email or book a free 15-minute call on our “get started” page and I’d love to chat with you about your goals and give you some tips to get you on the right path!

Stay Strong and Stay Healthy!

Dr. Jayson Dahlquist DPT, CAFS, Running Specialist/Coach