The Spleen Effect in Freediving: Why Later Holds Feel Easier

The spleen effect freediving instructors describe is the release of extra red blood cells into your circulation when your spleen contracts during repeated breath-holds. More red cells means your blood can carry slightly more oxygen, typically a few percent more. The response builds over a series of holds and fades again once you go back to normal breathing, which is one reason your third or fourth breath-hold in a session often feels easier than the first.

It has been measured many times, and it’s also easy to overstate. Below is what’s reasonably well established and what it means for how you warm up.

What your spleen normally does

Your spleen sits in the upper left of your abdomen, tucked under the lower ribs, roughly the size of a fist. Its day job is filtering blood: it removes old and damaged red blood cells and plays a part in your immune system.

It also holds a reserve of blood with a high concentration of red cells. In some animals this reserve is enormous. Horses release large amounts of stored red cells from the spleen during hard exercise, and diving seals have big spleens that empty into the circulation on long dives. Humans carry a much smaller reserve, but the same mechanism exists.

How breath-holds make the spleen contract

The spleen is wrapped in a capsule that can tighten. During a breath-hold, signals from the sympathetic nervous system contract it and push some of the stored, red-cell-rich blood into circulation. Falling oxygen appears to be one of the main triggers, and the response forms part of the wider mammalian dive reflex, alongside the slowing heart and narrowing blood vessels.

Ultrasound studies have shown the spleen getting measurably smaller after a series of breath-holds, with haemoglobin and haematocrit (the share of your blood made up of red cells) rising by a few percent at the same time. Hard exercise and high altitude can trigger a similar response.

A few percent doesn’t sound like much. Over a long static or a dive to depth, a little more oxygen-carrying capacity, and possibly a little more buffering of acid in the blood, is a real if modest advantage.

How fast the spleen effect builds and how long it lasts

The effect isn’t instant. Studies generally find it builds over the first few holds of a series, with much of the change in place after three to five near-maximal holds, depending on the person and the protocol.

It also doesn’t last. Once you return to normal breathing, the spleen refills and goes back towards its resting size. Several studies put that recovery in the order of ten minutes, though the timing varies between people and protocols. In practical terms, a warm-up done half an hour before your main hold has mostly worn off by the time you need it.

Why later holds feel easier: the spleen is only part of it

If your best holds come after a few warm-ups, the spleen probably deserves some credit. It isn’t the only reason:

• The dive reflex settles in. The heart rate drop and vasoconstriction tend to come on faster and more strongly after the first hold or two.
• Your mind settles. The first hold carries the nerves of starting. By the third, you know what the urge to breathe feels like and it’s less alarming.
• The routine gets smoother. Breathe-up, final breath, letting go of the shoulders: each repetition makes the sequence more automatic.

When divers say their spleen “kicked in”, they’re usually feeling a mix of all of these. The practical response is the same either way: warm up properly.

A sample dry warm-up before a longer hold

This is one common way to structure a dry static warm-up. It’s an example, not a prescription, and coaches vary. The times assume a dry personal best of about 2:30, so scale them to yours.

Step	What you do	Example time
1	Relaxed breathing, lying down	3:00
2	Easy hold, about 40% of your best	1:00
3	Recovery breaths, then calm breathing	2:00
4	Hold, about 50% of your best	1:15
5	Recovery breaths, then calm breathing	2:00
6	Hold, about 60% of your best	1:30
7	Longer rest before the main effort	3:00–4:00
8	Main hold or the start of your table	Your plan

A few rules go with it. Breathe normally between holds, with slow, relaxed breaths and no hyperventilation. Keep the gap before the main hold fairly short, since the effect fades. And don’t treat the warm-up as a series of mini-tests; the point is to arrive at the main hold relaxed. For a full home programme, see dry static apnea training.

In the pool, the same idea applies to dynamics: a few easy, short swims before your longer ones, with your buddy watching every one. Our pool training guide has session templates you can borrow.

Safety: Warm-up holds make later holds feel easier, but they don’t make you immune to blackout. Do dry holds only on land, lying down. In the water, every hold needs a trained buddy watching you from the surface, one diver at a time.

Can you train a bigger spleen effect?

Possibly, to a degree. The best-known evidence comes from the Bajau, the so-called sea nomads of Southeast Asia, who have dived for food for generations. A 2018 study found their spleens were larger on average than those of a neighbouring community that doesn’t dive, and linked this to genetic differences, which points to natural selection over many generations rather than training alone.

Within one lifetime, some research suggests trained breath-hold divers have larger spleens or stronger spleen responses than non-divers. It’s hard to separate the effect of training from the kind of people who take up freediving in the first place. We’re not aware of any supplement or gadget shown to boost it, so ignore anyone selling one.

What you can influence is the oxygen-carrying capacity you start with. Anaemia is common in India, particularly among women, and low haemoglobin means less oxygen in every litre of blood before the spleen does anything at all. If you’re unusually tired or breathless, a routine blood count is a better first step than any breathing trick. And if you’ve recently had an illness that can affect the spleen, such as malaria or glandular fever, check with your doctor before hard breath-hold training.

How to use the spleen effect in your next session

• Plan three or four progressive warm-up holds before anything long, and keep the gap to your main effort down to a few minutes.
• Note in your freediving log which hold felt best. Many people find it’s the third or fourth, and that pattern helps you plan future sessions.
• If you’re training for a trip, use the same warm-up routine in the pool that you’ll use on the line, so it becomes automatic by the time you’re floating at the buoy.

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