# 5 Physiological perspectives on extreme endurance sports

During extreme endurance sports the body has significant physiological demands placed on it. Although an ultra-marathon is a race usually between 50 and 100 km without a break, there can be great variability in distances. For example, the Comrades Marathon in South Africa is 90 km, while the Marathon des Sables in the Sahara Desert is 250 km. The Marathon des Sables takes place across 11 days in Morocco. Nine of these days are in the Sahara Desert, running or walking across sand and rocks. In addition to having to cover 250 kilometres, the participants must carry all their food and equipment and sleep overnight in a tent.

Figure 3

The distance covered and duration of exercise during an ultra-marathon puts immense strain on the muscular, cardiovascular and other body systems and requires a large amount of energy. If a runner is unable to meet the energy needs of the activity they’ll be in a situation where they start to break down their skeletal muscle and fat stores to provide fuel for the body (Knechtle and Nikolaidis, 2018). In this way, the body starts to eat itself and muscle lost to energy production, including to the heart muscle, can significantly impair performance. Dehydration can also be a huge problem, particularly when there are extremes of heat, such as in the Sahara Desert. A runner can lose up to 2.8 litres of sweat an hour and it is a challenge for them to replace this fluid loss while still running and prevent the resulting performance loss (Bottoms, 2021). In Activity 4, Nick Tiller describes the physiological impact of an ultra-marathon.

## Activity 4 The cost of extreme endurance sports on the body

Allow about 30 minutes

First, listen to Audio 2 Endurance from Healthcheck on BBC World Service, from 14:51 to 18:40.

Next, note down what Tiller says (from his experience) can happen to the body around 25 miles, 50–60 miles, and after the ultra-endurance event.

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### Comment

Tiller outlines both the negative effects of extreme endurance running on the body with some positive effects such as improved cardiovascular health, aerobic fitness and quality of life. Three physical impacts he highlights are:

- after 25 miles, muscle soreness develops due to tightness and microtears in the muscles

- after 50 to 60 miles, the digestive system (which is key to rehydration and delivery of energy from food) can shut down, as energy for the working muscles is prioritised by the body. This means that any food or drink consumed stays in the gut, causing symptoms such as nausea and stomach cramps

- at the end of the race, inflammation in the body occurs owing to the oxidative stress caused by the huge amounts of oxygen that have been consumed.

The damage to the body caused by extreme endurance sports is generally reversed after a few days (Knechtle and Nikolaidis, 2018), but there is limited research on the long-term health impact on the heart. However, one study from Gajda and colleagues (2020) found that damage to the muscles and liver, as well as inflammation was reversed after 10 days, and that many years of intensive training and ultra-marathon running did not have permanent negative effects on a runner’s heart.

## Find out more

To find out more about what running 100 miles a day can do to the human body, you could read the article ‘I ran 100 miles in a day – this is what happened to my body’ (Tiller, 2018), which also includes links to relevant research. Reflect on how the article develops some of the ideas covered in this section of the course. For example, think about the factors that influence the amount of muscle damage caused during ultra-marathon running and how nutritional strategies can support participants in ultra- endurance events.

To find out more about the physical limits of the human body, you could read the BBC Sport article ‘Ultimate limit of human endurance found’ (Gallagher, 2019). Consider the factors that contribute to running economy and why it is important, and the limits on how much energy the body can produce.

OpenLearn - Extreme endurance performances
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