The idea is that when you run, the flexible, tough tissue that cushions your knee joints, called cartilage, takes a pounding.

這樣的理論來自於，在你跑步時，這個有彈性、堅韌的緩衝墊，也就是軟骨，會承受一定的衝擊。

And over time, that cartilage supposedly wears down, which makes your bones rub together, and leads to the pain, stiffness, and swelling of osteoarthritis.

長久下來，這軟骨便會被消耗掉，讓你的骨頭產生摩擦，最終導致骨關節炎的疼痛、僵硬跟腫脹。

But is this actually true?

但真的是這樣嗎？

Past studies that compared runners to non-runners, sometimes collecting data over a couple of decades, have found mixed results.

過去有研究將跑者與非跑者進行比較，有時候經過數十年的資料蒐集，最後的結果卻是不統一的。

A few have found that there's more risk of knee osteoarthritis in specific groups of runners, like in men younger than 50 who run more than 32 km a week.

有幾個研究顯示，某些特定群組的跑者會有較高的風險罹患骨性關節炎。比如一週跑步距離超過 32 公里、年紀小於 50 歲的男性。

But lots of papers comparing long-term runners to swimmers, non-runners, or sedentary people didn't turn up evidence that running will doom you to arthritic misery.

但是其他研究比較長期跑步的人與游泳愛好者、非跑者或是久坐不動的人，卻沒有發現足夠的證據證明跑步會讓你得關節炎。

In some cases runners even seemed to be less likely to get arthritis.

有些研究甚至顯示跑者比較不可能患關節炎。

So could running actually protect your joints somehow?

所以，跑步到底能不能保護你的關節呢？

To find out, a study published in 2016 looked at what's happening inside your knees when you run.

為了找出答案，2016 年有項研究就觀察了人在跑步時膝蓋內的運作。

Scientists gathered a group of male and female runners, younger than 30 with no history of knee problems.

這些科學家找了一群年齡在 30 歲以下、膝蓋沒有受過傷的男性及女性跑者。

And brought them in for two experiment sessions over two days.

帶他們做為期兩天的兩項實驗。

They started each session by collecting a blood sample and a bit of synovial fluid, the natural lubricant inside the knee joint.

他們先蒐集了血液樣本還有滑膜液，也就是膝蓋關節的天然潤滑油。

Then they had the participants spend 30 minutes running on a treadmill one day, and 30 minutes sitting on another day.

然後一天請跑者花 30 分鐘在跑步機上跑步，另一天則是坐 30 分鐘。

Afterward they took more samples.

然後再蒐集樣本。

Getting a useful amount of fluid from healthy knees, turned out to be pretty tricky.

要從健康的膝蓋採集夠用的液體顯然有些難度。

And the researchers only ended up with complete data for 6 people.

這些研究者最終只有 6 組完整的數據。

But the results are still interesting.

但是結果還是蠻有趣的。

The scientists were looking for molecules related to inflammation, because extra inflammation has been linked to the development of arthritis.

這些科學家在找的是跟發炎有關的分子，因為過度的發炎最終會導致關節炎的產生。

They were also measuring a compound called cartilage oligomeric matrix protein, or COMP, which can be a marker of arthritis if there's a bunch of it in your synovial fluid.

他們也在測量一種叫做軟骨寡聚基質蛋白 (COMP) 的複合物，因為如果你的滑膜液中有些 COMP，代表你有可能有關節炎。

After running, the subjects had less of these molecules in their knees, and more in their blood, spread out in their bodies.

跑步過後，這些研究對象的膝蓋裡有較少的發炎分子，血液裡有較多的發炎分子，被分散在身體裡。

Sitting, on the other hand, slightly increased concentrations of COMP and some other inflammatory molecules in their knees.

另外，久坐不動，反而會讓 COMP 的濃度提高，膝蓋裡也存有其他的發炎分子。

It's hard to tell exactly what this means.

這樣的結果很難解釋。

But it seems like running might squeeze inflammatory compounds out of your knee, which could reduce cartilage damage and arthritis.

不過看起來跑步似乎能夠將膝蓋中的發炎複合物排出，可能降低軟骨損傷及關節炎。

But this study did have a pretty tiny sample size, so... Jury's still out!

但是這項研究的樣本數不足，所以... 尚未定論！

But if you like running and it makes you feel healthy, the next time someone says, "But you'll ruin your knees!"

如果你喜歡跑步而且它能夠讓你覺得更健康，那下次有人對你說：「跑步會傷膝蓋！」的時候。

Take it with a grain of salt.

就抱持著懷疑的態度吧。

Thanks for asking and thanks especially to all our patrons who keep these answers coming.

謝謝以上的提問，也特別謝謝各位觀眾的提問。

For more running-related science, check out this other SciShow video, where Hank explains why you get that sharp pain in your sides sometimes.

若是你想看更多和跑步有關的科學影片，看看這部影片吧！Hank 會在影片中解釋為什麼有時跑步，腹側會疼痛。