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? Compare and contrast the structure and function of the three types of skeletal muscle fibers.

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Hi everyone, welcome back. Let's look at our next question. It says which of the following is or are relatively high in slow twitch muscle fibers as compared to fast twitch muscle fibers. When we look at our answer choices, let's keep in mind that we have choice D. Being all of the above. So let's remember that. That's a possibility. Well we're going to recall from our content videos that slow twitch muscle fibers. As of course their name lets us know contract slowly, but they also maintain those contractions for a longer period of time. Um As we recall, muscle fibers need a TP to allow contraction to happen. A TP allows myosin to bind to the acting filament and then let go. Which is what drives muscle contraction. So they need lots of 80 p. Being steadily produced over a long period of time. So that means that slow twitch muscle fibers utilize aerobic respiration to provide for their A. T. P. Needs Aerobic respiration doesn't doesn't produce a T. P. Um It produces a relatively slow rate but produces a lot of a T. P. So aerobic respiration allows the slow twitch fibers to sustain their exertion over longer periods of time since it's steadily going along producing lots of a. T. P. But to drive that aerobic respiration um we do need a steady supply of oxygen. Now we want to compare slow twitch muscle fibers to fast twitch muscle fibers and of course sometimes you need muscles to contract quickly right away. Which calls for a T. P. At a quicker rate than aerobic respiration can supply. So as a result, as we recall, those fast twitch muscle fibers turn to anaerobic respiration in the form of glycol icis. And that produces a teepee very quickly but less a teepee overall. So the fast twitch muscle fibers can contract very quickly without burst of a quick a teepee from like Alexis, but they burn through it very quickly also so they tire more quickly. So when we look for our answers at what we'd find in relatively higher levels and slow twitch muscle fibers, we want to focus on the fact that slow twitch fibers require a steady supply of oxygen to drive aerobic respiration. So with that in mind, let's look at our answer choices. Choice A says mitochondria. While mitochondria are those factories that are producing a teepee where aerobic respiration takes place. So since we are using aerobic respiration and our slow muscle fibers, mitochondria, we'd expect to see in higher levels in those types of fibers. Choice B. Myoglobin, myoglobin is the protein that binds oxygen in those muscle fibers. And since we need a steady supply of oxygen, we would also expect to see higher levels of myoglobin in our slow twitch muscle fibers. And finally, choice see blood vessels while blood vessels are what is going to be delivering the oxygen to those slow twitch fibers. So again, to provide that steady stream of oxygen, we will expect to see more blood vessels in slow twitch fibers. So our correct answer is going to be choice D all of the above. Since all of these things mitochondria, myoglobin and blood vessels, we'd expect to find in relatively higher levels in slow twitch muscle fibers, as compared to fast twitch muscle fibers. See your next video.

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Key Concepts

Skeletal Muscle Fiber Types

Muscle Structure and Function

Adaptation to Training