Understanding the Physical Effects of Running a Marathon
Global Running Day: Here’s what running a marathon really does to your body

Image: The Independent
As the London Marathon approaches, many runners are curious about the physiological changes their bodies undergo during the race. Key effects include increased heart and breathing rates, muscle micro-tears, elevated sweat production, and a shift in metabolism from glycogen to fat as energy sources, leading to potential fatigue.
- 01During a marathon, heart rate and breathing rate significantly increase to deliver more oxygen to the muscles.
- 02Micro-tears in muscles occur due to repetitive movements, leading to delayed onset muscle soreness post-race.
- 03Runners experience increased sweating as their bodies regulate temperature, which can result in dehydration if fluids are not replenished.
- 04Metabolism shifts from glycogen to fat as the race progresses, with glycogen stores depleting around mile 18-20, potentially causing fatigue.
- 05Cardiac drift may occur, indicating dehydration and overheating, leading to increased heart strain.
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As the London Marathon approaches, many runners are preparing for the physical challenges of the race. Francesca Bagshaw, a performance physiologist at Nuffield Health MIHP, explains several physiological changes that occur during a marathon. Runners experience a significant increase in both heart and breathing rates to meet the muscles' demand for oxygen. This heightened activity can lead to cardiac drift, a condition where heart rate rises disproportionately, often due to dehydration. Additionally, the repetitive nature of running causes micro-tears in muscles, resulting in delayed onset muscle soreness within 24-72 hours post-race. As runners exert themselves, their bodies also increase sweat production to regulate temperature, which can lead to fluid and electrolyte loss. Furthermore, metabolism shifts from burning glycogen to fat as glycogen stores become depleted, particularly around mile 18-20, leading to fatigue and a phenomenon known as 'hitting the wall.' Understanding these changes can help runners prepare effectively for their marathon experience.
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Understanding these physiological changes can help runners better prepare for the marathon, potentially improving their performance and reducing the risk of injury.
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