跟讀練習: How Caffeine Affects Exercise & Athletic Performance - 通過影片學習英語口語

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Caffeine is one of the most widely used psychoactive substances in the world.

Now, most of the time we think of caffeine as a stimulant that could help us feel more alert or awake, or get us through the workday, if you will.

However, caffeine as a performance enhancer for exercise, sports, and athletics is getting more and more attention,

with people using energy drinks or pre -workout supplements that contain caffeine, with the hopes in that it could maybe improve endurance,

or improve weightlifting capabilities or even just improve performance in certain sports.

So in today's video we're gonna talk about if caffeine can actually improve exercise and athletic performance, how it could possibly do this,

and the amount that you would need to take in order to get some of these potential benefits.

It's going to be a stimulating one, so let's do this.

So let's start by answering the first big question.

Can caffeine improve exercise and athletic performance?

Now there have been countless studies done on this, a handful of which we'll include in the description below, but the overall answer is yes, caffeine can improve exercise and athletic performance.

And it seems that these benefits of caffeine can be applied to a wide range of different exercises.

For example, caffeine has been shown to improve exercise capacity at prolonged submaximal exercise,

things lasting longer than 90 minutes like a long run or a long bike ride, but it has also been shown to improve it at the mid -range or more of a little bit higher intensity,

something that you might only be able to do for like 20 to 60 minutes.

Not only that, it's been also shown to improve at the higher intensity, it's like that high intensity interval timeline of one to five minutes.

So that you can see caffeine

and these improvements can be applied to a wide range of cardiovascular dominant type exercise

that requires a lot of output from the heart and cardiovascular system.

Not only that, caffeine has also been shown to improve movement velocity during resistance training, so moving weights faster, and also has been shown to improve reaction time.

So you can see how these characteristics or improvements in those two characteristics could be applied or be beneficial to weight training,

or sports that require explosive movements like throwing or jumping, or maybe even a sport that might require improvement in reaction time,

like maybe you're a martial artist and you need to react to a ninja kick coming towards your head.

But how is caffeine doing this?

What is it doing inside of your body that is accounting for these potential performance benefits?

Well, we're going to take a look at two main mechanisms.

One is how caffeine is a stimulant of the central nervous system, and the central nervous system or CNS in anatomy just includes the brain and the spinal cord.

And then we'll also look at how caffeine could possibly affect muscle tissue.

So let's start with the central nervous system by zooming in to what we'd find in your brain.

Now to be fair, this is a very simplistic drawing of what you'd find in your brain.

Really I just drew one neuron or one nerve cell, but the reality is you'd find billions of these neurons throughout your brain and nervous system.

But we actually only need to take a look at one to understand how caffeine affects athletic performance.

So if we take a look at this extension from the neuron, this is called the axon.

And I've drawn some branches here and I've zoomed into one of those branches by drawing it up here.

It's called the axon terminal, just the end of the axon and there are multiple receptors or chemicals that you find throughout your brain and nervous system.

We're obviously gonna focus on the receptor that has to do with caffeine, and I've drawn this in as these little green Ys, and these green Ys represent the adenosine receptor.

Now the blue diamond is the actual adenosine molecule which will obviously bind to the adenosine receptor, like a lock and key analogy.

You need a very specific shaped key to fit into a very specific shaped lock in order to turn

or activate that lock.

Now, it's thought that adenosine will build up on the outside of your neurons as the day goes on.

And maybe you've heard of something called ATP, which stands for adenosine triphosphate.

ATP, or adenosine triphosphate, is the energy currency for your cells.

And your neurons actually burn through a lot of energy or ATP throughout the day. So again,

that adenosine starts to build up on the outside of the neurons and then can start binding to those adenosine receptors.

But what does that cause to have happen?

Well, when adenosine binds to the adenosine receptors, it suppresses the activity of your neurons.

So your neurons will fire less frequently, less intensely.

And to you, that feels like you might feel a little bit more tired or fatigued, less focused, less alert.

But we bring caffeine into the picture.

You ingest it in some way, it gets into your bloodstream.

And we've got this nice little blood vessel coming into the brain here with our little red caffeine molecules

and the caffeine will diffuse from the bloodstream and bind to one of those adenosine receptors.

It's close enough in shape to the original adenosine to bind, but not close enough to actually activate the receptor.

Maybe you've put a key into a lock that.. fits in there but not quite enough to actually turn the lock.

Think of caffeine as doing that as getting in that lock, getting in that receptor and blocking it, so then adenosine can actually get into those receptors.

So caffeine blocks the effects of adenosine and therefore has these opposing effects.

Instead of feeling tired, less alert, more fatigued, you get increased awareness,

increased alertness, you're more focused and you can definitely apply those characteristics to athletic performance

and performing better in certain sports to be more focused and more alert.

But it doesn't only just stimulate or increase awareness, caffeine also suppresses your perception of effort.

Meaning, you're exercising at a certain intensity, it will feel a little bit less of an effort

or you feel like you're putting less effort in than you would without caffeine.

Now, caffeine also suppresses your perception of pain to a certain degree.

And so if you also suppress pain to a certain degree, we've all had those moments when we've been exercising

or playing sports where it's uncomfortable or maybe even causing a little bit of pain.

So if caffeine can also suppress the pain a little bit, again, you're going to be able to push it a little bit further and therefore increase athletic performance. So hopefully

that gives you a good baseline understanding on how caffeine works

on the central nervous system to help you feel a little bit more focused and alert during sports and exercise, as well as helps to diminish that perception of effort and even pain and discomfort.

But how does caffeine affect your muscle tissue?

Well, there are studies that suggest that caffeine affects intramuscular calcium or the calcium inside of your muscles.

Now this is significant because calcium plays a huge role on how your muscles contract.

So let's quickly explain this and then apply it to caffeine.

If you take a look at this biceps, you can see that it's made up of multiple muscle fibers or muscle cells.

And if we zoomed into an individual muscle cell and into the myofibro, we would see that we have these little contractile subunits called sarcomeres.

And these sarcomeres are stacked end to end to end lengthwise throughout the muscle.

And this is about what the inside of a sarcomere would look like with our little whiteboard drawing here.

But this is where we can figure out how calcium works.

So taking a look at this picture of the sarcomere, you can see the thick filament in red.

And it kind of looks like a bundle of golf clubs

and each individual golf club would be a myosin molecule which is a contractile protein.

Now keep in mind I will mention some of the names here, but you actually don't have to memorize all these names to understand the concepts, I'm just going to mention the names for all the anatomy and physiology nerds out there.

But those myosin molecules

or the myosin heads where you'd actually hit the ball with the golf club want

so badly to bind to the thin filament which is in green

and it looks like little circular beads slightly twisted and each little bead or circle would be an actin molecule, another protein.

Now the problem here is that the myosin

and the actin can't bind together yet because that blue line that's wrapping around the thin filament or those actin molecules,

this is called the troponin tropomyosin complex or just TTC, it's blocking those binding sites.

And this is what a muscle actually looks like at the microscopic level in the resting state.

But, when the nerve sends the signal to the muscle to make it contract, what happens is is calcium within the muscle cell

and therefore within the sarcomere will actually be released and binds to the TTC,

that blue line, and shifts it slightly out of the way so now myosin and actin can bind and myosin ratchets.

And you get this ratcheting effect throughout all those sarcomeres and that in turn would shorten the muscle and create the contraction.

So, what does this calcium have to do with caffeine?

Well, there are studies that suggest that caffeine can enhance

and increase the amount of calcium released within the muscle cell and therefore within the sarcomere, thereby enhancing the contraction of the muscle.

And this could in part explain why they were seeing increases in contraction velocity during resistance training

when people were supplementing with caffeine.

And you could obviously apply this to being beneficial to weight training

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and even sports or athletic events that require explosive movements like we mentioned earlier,

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throwing, jumping, sprinting, etc. Caffeine can also affect the cardiac muscle tissue within the heart, causing that cardiac muscle to contract with more force during each beat

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and therefore delivering more blood and oxygen to your skeletal muscles throughout your body.

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And you can see if you get more blood and oxygen to working skeletal muscles, there could be multiple benefits or enhancements to different types of exercises and athletic events.

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So how much caffeine do you need in order to get some of these benefits?

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Well, it used to be thought

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that you needed to take as much as 5 to 6 milligrams of caffeine per kilogram of body weight.

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So I weighed in at about 184 pounds this morning and if we converted that to kilograms, that put me at just under 84 kilograms.

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And so, if I went with a 6 milligrams of caffeine per kilogram of body weight, that'd be 6 times 84 and I'd be taking over 500 milligrams of caffeine.

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Now, I don't know about you but

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that amount of caffeine for me would be a lot and I'd likely just be bouncing off the walls.

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Now, luckily, the more recent research has shown that you need much less than that to get some of these performance benefits,

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almost half of that, like 2 to 3 milligrams of caffeine per kilogram of body weight.

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So, if I went with a three, I'd be taking about 250 milligrams.

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If I went with a lower end at two, I'd be taking in about 167 -ish milligrams of caffeine.

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Now, most of the pre -workout supplements actually have about 200 milligrams of caffeine, which is a pretty good starting point.

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But if you're one of those that's very caffeine naive, you don't take a lot of caffeine or maybe you're a little more sensitive to it,

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you could start even lower at like a one to two milligram of caffeine per kilogram of body weight

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and in these levels

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that we're talking about two to three milligrams per kilogram of body weight are all well studied

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and are relatively safe for most people but

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if you continue to push the level eventually you're just going to get to creating side effects

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and even potential safety concerns

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because caffeine does not have what we'd call a dose response

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relationship meaning the more you take the more performance benefits for exercise and athletics that you're going to get.

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You're going to get to a point where that peaks out

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and then you're just going to be dealing with side effects and again potential safety concerns.

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And another thing we need to mention is timing.

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When should you take the caffeine?

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Caffeine is rapidly absorbed with about 99 % of it making it into the bloodstream within about 45 minutes of ingestion.

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So you should take it about 30 to 60 minutes prior to exercise

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or whatever sporting or athletic event you're trying to get some of these caffeine induced benefits from.

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But what if If you're like me and you don't like to take caffeine every single day, maybe you don't drink a lot of coffee or other caffeinated beverages and personally,

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I just don't like the idea of feeling beholden to something

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that I could potentially develop a tolerance or dependence to and that can happen with caffeine.

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Anyone who's been on caffeine consistently or for an extended period of time

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and then they've cut it out cold turkey has likely noticed some of those withdrawal symptoms like headaches, irritability and other potential withdrawal symptoms.

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Now, even though I don't like taking caffeine every day, it's still extremely hard for me to ignore some of these potential performance benefits.

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So what do I do?

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I tend to selectively pick and choose

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when I'm going to take about 200 milligrams of caffeine and they're generally centered around more competitive days.

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So on my regular training days, I don't usually take any caffeine.

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But if I know I'm going to run say like an obstacle course race on a Saturday

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or maybe have a really competitive game of basketball with my friends, I'll take some caffeine 30 to 60 minutes prior to those events.

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And so for me, I'm taking it at most one to two times a week.

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And that's more of just a personal choice for me to try to kind of avoid any

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or reduce my risk of developing the dependence or tolerance to caffeine.

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But that does not mean that you can't take caffeine every day.

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Plenty of people do it.

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Plenty of people take pre -workout almost every single day, drink their coffee every single day, and that's okay, and that works for them.

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You just have to also realize that if you decide to cut back on it or cut a cold turkey, there is some of the risk to developing some of those potential withdrawal symptoms.

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So hopefully that gave you a good understanding of how caffeine can help with exercise and athletic performance.

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And I wanna leave you guys with an incredible learning opportunity.

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And that's by saying thank you to the sponsor of today's video, Brilliant.

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We'll also include that link and the info in the description below.

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And I do want to mention that we do have another caffeine video

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that we've done previously

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that goes into a little bit more of the interactions in the central nervous system

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and talks a little bit more about the potential side effects.

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So, we'll link that to this video.

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And I also want to say thank you all so much for your support and watching all of our crazy

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anatomical and physiological videos.

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We really appreciate it and we couldn't do this without all of you.

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So, if you want to like, we definitely appreciate that.

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If you're not subscribed and you want to, go ahead

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if you feel the need and of course leave some comments below and we'll see you next time

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通過這個影片，你不僅能瞭解咖啡因對運動表現的影響，還能鍛鍊兩項關鍵英語口語技能：一是聽懂學術性內容的能力（如“中樞神經系統”“腺苷受體”等專業表達），二是模仿自然口語節奏的技巧。這些技能能幫你在英語口語練習中更自信地應對複雜話題。

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影片中存在不少連讀和弱讀現象，比如“caffeine is”連讀為/ˈkæfiːnɪz/，“a lot of”弱讀為/ə lɒt əv/。此外，“adenosine triphosphate”這類長單詞的重音位置（/əˈdenəsiːn traɪˈfɒsfeɪt/）也需注意。這些細節是提高英語發音的關鍵，多聽多模仿能讓你的口語更地道。

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模仿影片 speaker 的節奏和重音能讓你的口語更自然。比如，在說“caffeine can improve exercise and athletic performance”時，要強調“improve”和“performance”；講“it's going to be a stimulating one”時，用升調突出“stimulating”。你可以用英語影子跟讀的方法，跟著影片逐句重複，感受母語者的語流。這是看影片學英語的高效技巧，堅持一週就能明顯感受到進步！

影片中的語法

說話人最常用的結構，並附上影片中的原話：

結構	影片中的用法
條件句 if + 從句，will/would + 動詞 — 條件及其結果	if I went with a three, I'd be
現在完成時 have/has + 過去分詞 — 過去發生但與現在仍有關聯的事	have been · has been shown · has also been shown
被動語態 be + 過去分詞 — 強調發生了什麼，而不是誰做的	can be applied · has been shown · been shown
定語從句 who / which + 從句 — 補充說明人或事物	molecule which will · molecule which is · filament which is

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跟讀法 (Shadowing) 是一種有科學依據的語言學習技巧，最初開發用於專業口譯員的培訓，並由多語言者Alexander Arguelles博士普及。這個方法簡單而強大：您在聽英語母語原聲的同時立即大聲重複——就像是一個延遲1-2秒緊跟說話者的影子。與被動聽力或語法練習不同，跟讀法強迫您的大腦和口腔肌肉同時處理並模模擬實的講話模式。研究表明它能顯著提高發音準確性，語調，節奏，連讀，聽力理解和口語流利度——使其成為雅思口語備考和真實英語交流最有效的方法之一。

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跟讀練習: How Caffeine Affects Exercise & Athletic Performance - 通過影片學習英語口語

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你能學到什麼？

注意這些發音現象

像母語者一樣表達

影片中的語法

什麼是跟讀法？