Why Do We Get Tired When Running

When I go for a run, I often find myself wondering why I get so tired even after a short distance. It turns out there are several reasons why running can leave us feeling exhausted. Let’s explore the science behind why we get tired when running.

The Role of Oxygen

During running, our muscles require more oxygen to produce energy. As we increase our pace, our breathing rate also increases to supply our muscles with the necessary oxygen. However, there comes a point where our muscles cannot get enough oxygen, leading to the production of lactic acid. This buildup of lactic acid can contribute to that burning sensation and fatigue we often feel during intense runs.

Energy Depletion

Running depletes our energy stores, especially when we engage in longer or more intense runs. Our muscles primarily rely on adenosine triphosphate (ATP) for energy, which is produced through the breakdown of glucose and fat. As we continue running, our energy reserves diminish, leading to fatigue and the sensation of hitting a wall. This is often referred to as “hitting the wall” in the running community, and it can be a challenging experience for many runners.

Heat and Dehydration

When we run, our bodies generate heat, especially during vigorous exercise. To regulate our temperature, we sweat, which is our body’s way of cooling down. However, excessive sweating can lead to dehydration, causing our blood volume to decrease. This reduction in blood volume makes it harder for our heart to pump blood to our muscles, leading to increased fatigue and a decrease in performance.

Mental Fatigue

Running is not just physically demanding; it can also be mentally taxing. The constant effort and focus required to maintain form and pace can take a toll on our mental resources. As we push ourselves during a run, our brain’s glycogen stores become depleted, leading to mental fatigue and a decrease in motivation and willpower.


Understanding why we get tired when running can help us better prepare for our runs and improve our performance. By optimizing our breathing, fueling our bodies with the right nutrients, staying hydrated, and training our minds to endure mental fatigue, we can enhance our running experience and push our limits further. So, the next time you feel tired during a run, remember that it’s a complex interplay of physiological and psychological factors contributing to your fatigue.