Most people think the pump is caused by blood rushing to your muscles, but that’s incorrect.

What Causes The Pump?

Written by Russ Howe PTI, and most recently updated 1 day ago.

2 min read

I’ve been lifting weights for over 30 years, but I can still remember the first time I felt the pump.

Sleeves bursting.

Testosterone flying.

People screaming.

Okay, maybe I’ve exaggerated this experience as the years have rolled by, but let’s just say it felt fantastic. Heck, even the great Arnold Schwarzenegger described like this:

(I hope you read that in his voice.)

what causes the pump

But here’s where things get weird…

Most people believe that the pump is caused by blood filling up your muscles, and that’s dead wrong!

The pump is actually caused by interstitial fluid, which is a solvent-like solution that sits outside of the muscle cells. Interstitial fluid consists of water, salt, amino acids, cellular waste, coenzymes, hormones, neurotransmitters, white blood cells, sugar, and fatty acids, and it makes up about 26% of the liquid in your whole body.

It spills into your muscles when the body triggers a process called osmosis.

When you are performing exercise, your body starts to break down nutrients in order to use them for fuel, which causes a build-up of waste products inside the muscle cell (metabolites). It’s these metabolites which eventually trigger the interstitial fluid to temporarily rush inside the muscle cell, enabling you to spend the next 30-45 minutes looking even more awesome than when Rambo face-fucked a helicopter with a tank.

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I’m Russ. I’ve been a personal trainer since 2002, and I own

My job is to simplify fitness for my readers.

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