Why do you get tired when you run?

When you run, your body goes through a series of physiological changes to adapt to the increased demand for energy and oxygen in your muscles. Here is a breakdown of why you feel tired when you run:

1. Energy Use: Your muscles need energy to function. They get this energy from a molecule called adenosine triphosphate (ATP). When you run, your muscles use ATP much faster than when you're at rest, and after a certain point, your body struggles to produce ATP at the rate your muscles are using it. This contributes to fatigue.

2. Oxygen Consumption: Running increases your muscles' demand for oxygen. Oxygen is essential for the metabolic processes that release energy from glucose or fat in your cells. As you run harder or longer, it can become difficult for your cardiovascular system to supply enough oxygen to the muscles. This lack of oxygen can lead to a sensation of tiredness.

3. Lactic Acid Buildup: When there's not enough oxygen available, your muscles produce energy anaerobically (without oxygen), leading to the production of lactic acid. An accumulation of lactic acid can change the acidity within the muscles, leading to discomfort and a feeling of fatigue.

4. Dehydration: When you run, you sweat as a way to cool down your body. Through sweating, you lose fluids and electrolytes, and if these are not replenished, it can lead to dehydration, making you feel even more tired.