Chasing the Pump Won’t Build More Muscle, According to a New Review

Who doesn't love a good biceps pump?

Even the most devout exercise enthusiasts among us, who insist they train purely to feel good, can't deny there's something satisfying about watching your arms inflate midway through a workout.

One of the original fans of 'the pump', Arnold Schwarzenegger, famously described it as ‘the greatest feeling you can get in a gym’ – alongside another comparison probably best left outside these pages.

We might not go quite that far. But seeing the immediate fruits of your labour in the mirror certainly feels good. The bigger question is whether that temporary swelling actually tells you anything about long-term muscle growth.

Exercise researcher Dr Milo Wolf, PhD in Sports Science has taken a look at the evidence.

‘When you go to the gym and lift weights, your muscles visibly get bigger. However, this superpower is short lived and you soon return to your normal human state, that is what we call 'the pump'.’

The pump is essentially a temporary increase in muscle size, sometimes referred to as transient hypertrophy.

According to Wolf, ‘The pump is an acute or short-lived alteration or change in the balance between intracellular and extracellular water balance during lifting. The veins that take blood away from your muscles are compressed reducing the blood flow away from your muscles. Meanwhile the arteries are continuing to deliver blood flow towards your muscles.’

‘This creates an increased concentration of blood within your muscles,' says Wolf. 'Which increases pressure and eventually more plasma is flowing into your muscle.'

'Importantly though, it's not the actual muscle fibre that is swelling but rather the gap between them, what we call the 'interstitium' that is swelling.'

Wolf compares the process to inflating a tyre: as more fluid accumulates in and around the working muscle, pressure increases and the muscle temporarily appears larger.

Sadly, those suddenly sleeve-splitting arms aren't permanent.

Wolf explains that some muscle swelling following a workout can remain for up to 48-72 hours, although the noticeable pump you experience during training will typically dissipate much sooner.

'If you've ever stopped lifting for a few days or weeks you'll notice pretty much instantly you get a little bit smaller.’

But temporary muscle swelling and permanent muscle growth are two different things. Which brings us to the question that actually matters.

There are reasons researchers have been interested in the relationship between the pump and hypertrophy.

Research published in Strength & Conditioning Journal has explored potential mechanisms through which cell swelling could contribute to hypertrophic adaptations.

Other studies have found associations between the amount of swelling produced by a workout and subsequent muscle growth.

One study published in The Journal of Strength & Conditioning Research followed 22 untrained men performing knee extensions. Researchers found a positive association between acute muscle swelling following an initial training session and hypertrophy after six weeks of resistance training.

Similarly, research published in Gait & Posture found that immediate swelling in two lower-leg muscles following resistance exercise was positively associated with longer-term hypertrophy.

That's interesting. But an association doesn't prove that the pump itself caused the muscle growth.

A 2025 review published in the Journal of Sport and Health Science examined proposed mechanisms of muscle growth, including metabolic stress and cell swelling. While acknowledging research linking greater post-workout swelling with subsequent hypertrophy, the authors concluded that there isn't currently enough evidence to say that achieving a greater pump directly increases muscle growth.

Mechanical tension remains the much more important consideration.

Probably not.

Wolf explains that despite some interesting findings, acute muscle swelling doesn't predict hypertrophy particularly well.

'The mechanisms regarding how much the pump actually matters for growth and why it does are still relatively poorly understood,' he says.

There's another problem when trying to apply these studies to your own workouts: researchers can objectively measure changes in muscle size using equipment such as ultrasound. You, meanwhile, are relying on how pumped you feel.

'In the case of the pump, we have minimal evidence that is relatively inconsistent, with the additional caveat that you are not an ultrasound.'

In other words, there's no good evidence that your subjective rating of an enormous pump corresponds neatly with the measurements researchers are taking – or that choosing whichever exercise gives you the biggest pump will produce the most muscle.

'Do not use the pump as a means to select a strategy over more important and more evidence-based principles like training of longer muscle lengths,' says Wolf.

If, for example, you're choosing between an exercise that trains a muscle effectively at longer muscle lengths and another that simply produces a better pump, Wolf argues that prioritising the latter could mean sacrificing a potentially more useful hypertrophy stimulus.

'We have a body of evidence of about 20 to 25 studies that suggest that longer muscle length training is likely to be better for hypertrophy,' says Wolf.

That doesn't mean the pump is completely meaningless, either.

'The only time I ever really pay attention to a pump besides getting a sick picture for my Instagram or YouTube is if I don't get any pump whatsoever from what is seemingly on paper a pretty reasonable protocol — that might be something worth paying attention to. Because there might still be some correlation between your pump and effectiveness. But, as long as you get a pump I wouldn't really pay much more attention.'

The takeaway? Enjoy the pump. Take the mirror selfie if you must. Just don't mistake temporarily bigger muscles for proof that you've found the ultimate muscle-building workout.

Prioritise progressive training, sufficient effort and exercises that challenge your muscles effectively through a useful range of motion. Let the pump be the satisfying side effect.

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