In 2023, Tigist Assefa of Ethiopia set a new record with a time of 2 hours, 11 minutes, and 53 seconds. Scientists, trainers, and athletes alike have wondered about the extent to which muscle structure and function contribute to success in athletes such as Assefa. What makes elite distance runners so good? Are their muscles somehow different from those of less successful athletes and non-athletes? To discover the relationship between muscle-fiber types and performance, researchers obtained tiny biopsies of the gastrocnemius of 14 elite distance runners, 18 trained but non-elite distance runners, and 19 untrained subjects. They categorized the fiber types as slow or fast. (At the time of the study, intermediate fibers had not been identified as a third type.) Some of their data are shown here (* means 𝑃<0.05; BioSkills 3). What conclusions can you draw from these data?

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Welcome back. Here's our next question. Four individuals are actively engaged in four different sports which are listed below. Which of the following sports is most likely to increase the proportion of slow twitch fibers. Well let's recall from our content videos that in muscles we have slow twitch and fast twitch fibers and the slow twitch fibers mainly use aerobic respiration. So that combination of glycol Asus and the Krebs cycle and that is a slower process. And you can help remember that by slow twitch slower process but generates more A. T. P. As you recall when you go through the Krebs cycle, you generate 38 ep molecules per molecule of glucose so they generate lots of 80 P. But going through Gladiolus and the Krebs cycle is a slower process. It also requires large amounts of oxygen so it's rate limited by how quickly the body can get oxygen to it to allow this process to continue. So slow twitch muscles are really good for long endurance type activities. Long distance running. Um Other things where you're not um rapidly burning up energy but you need that to last for a long period of time. Fast twitch muscles mainly rely on anaerobic respiration. So like hollis is only so it generates less A. T. P. But faster. So we recall that in glycol Asus we only generate to a tee pee molecules per molecule of glucose. Um but it does not require oxygen so it can very even though it generates less P. It can generate very very very quickly. It's a fast process and so that makes it ideal for activities sprinting. Um jumping, lifting heavy weights things where you need a quick burst of muscle movement and it doesn't need to last that long. Um In this process in the glycol Asus your end product is piru bait and the piru bait gets converted to lactate or lactic acid that builds up in the muscles which causes a burning sensation, soreness and that's actually a protective mechanism to keep you from over exerting and um overextending your muscles. So let's look at our answer choices and we're looking for which sport is most likely to increase the proportion of the slow twitch fibers. Um the ones that um generate more 80 p. But at a slower rate. Um And the proportion of slow versus fast fast twitch fibers is somewhat genetically determined in the individual but by repeatedly engaging in an exercise that uses one type of muscle over the other. You can increase the proportion of that muscle. So we look at Choice A. Is powerlifting. Powerlifting is going to use fast twitch muscle fibers since you need a burst of muscle movement to lift the weights and not over a long period of time. Choice B. Is sprinting sprinting also you want rapid acceleration. It doesn't need to last long. So that also prioritizes fast twitch muscles and to I see jumping also fast twitch um Choice D. Is distance running. And distance running would build up slow twitch muscle fibers. Um You run at a slower pace and you want to be able to endure and keep up that exertion over a long period of time. So you'd want the greater a TP production um even at a slower rate of the slow twitch muscle fibers, so which sport is most likely to increase the proportion of slow twitch fibers. Choice D. Distance running? Hope to see you in the next video.

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Key Concepts

Muscle Fiber Types

Genetic Variation in Muscle Composition

Training Adaptations