Hypoxic swim sessions: what are they and should you do them?

Heard a lot about hypoxic swim sessions, both good and bad, and wondering whether they are worth including in your training? BTF level 3 coach Matt Sanderson from Triathlon Coaching UK explains all


There’s something about the word ‘hypoxic’ that sends alarm bells ringing in my head! Most likely because I entered the triathlon world as a weak swimmer with major technique flaws following a period of teaching myself to swim front crawl some 14 years ago. The very thought of entering a hypoxic state is still enough to make me breathe a little deeper, just in case it’s my last for a while!


The term ‘hypoxic training’ refers to adapting to a reduced level of oxygen. In swimming terms, it refers to swimming more strokes without breathing. It was thought that by depriving your oxygen consumption you would slow the flow of oxygen to the working muscles. It was believed that this would lead to an improved aerobic capacity, ultimately leading to faster swim times.

When I asked my Monday swim squad what the term ‘hypoxic training’ meant to them, they mostly responded with ‘holding your breath as long as possible’. For me, here in lies the problem with this type of training. The name hypoxic seems to refer to ‘breath holding’ something we strongly advise our swimmers NOT to do!

Holding your breath increases CO2 in your system. CO2 build up can be dangerous and in extreme cases (many triathletes go to extreme lengths!) can lead to black outs. I am much more comfortable with asking swimmers to ‘control their exhalation’ allowing them to swim a greater number of strokes between breaths.

The key thing here is that swimmers should always be breathing out when their face is in the water. This is a basic technique that is poorly performed by many swimmers. It is common to see swimmers holding their breath during underwater swim video analysis like in figure 1 below. This really holds back their stroke development. The image on the left side shows how the swimmer isn’t exhaling at all, while on the right side the swimmer is correctly and continuously exhaling into the water. Delaying the initial exhale only increases the rate of exhalation when it finally starts.

Figure 1

Above image is bySwim Revolution https://www.swimrevolution.co.uk

Instead of encouraging swimmers to hold their breath we should encourage swimmers to slowly ‘trickle breathe’ continuously into the water. Using this approach can help a swimmer to take more strokes between breaths which is a really handy way of improving technique. It is the breathing stroke where we observe most flaws in technique so by reducing the number breathing strokes in training we can develop a more efficient ‘feel’ for correct technique. Trickle breathing for 5-7 strokes is a great way of being able to observe your own stroke – hand entry, catch set up and pull phase are all visible when not breathing.

Trickle breathing also builds an understanding of how much oxygen we actually carry in the lungs and often surprises swimmers how relaxed their breathing mechanics can be. Trickle breathing helps prevent forced breathing patterns and when performed consistently helps swimmers to relax, improving endurance capabilities as swimming is less effort.

One other reason why I prefer to have my swimmers trickle breathe rather than hold onto their breath is that by holding breath you inflate the chest cavity which can contribute to sinking legs, especially in more muscular swimmers.

So, from my triathlon coaching perspective there are benefits to using hypoxic methods, but these methods are more adaptations of how many people view the term hypoxic. Personally, I would encourage a swimmer to exhale slowly and continuously as soon as their face is in the water and to continue to do so until they are ready to inhale. This will mean encouraging the swimmer to take more strokes per breath but never involves holding their breath which is the key difference here.

I would always want to see my swimmers master the basic exhale into the water more efficiently before starting this adaptation of hypoxic training. You can then move onto introducing ‘trickle breathing’ but keep the volume low to start with as you will find it a little uncomfortable at the start.

Try the following trickle breathing set which is perfect prior to the main set:

Warm up

2-300 metres freestyle focus on exhaling into the water

Main set

1 x 50 breathing every 3rd stroke with focus on exhaling through the mouth only

1 x 50 breathing every 3rd stroke with focus on exhaling through the nose only

1 x 50 breathing every 3rd stroke with focus on exhaling through nose & mouth

See which you prefer and work with that during the next set:

6 x 50 metres as;

Lengths 1&2 breathe every 3rd stroke

Lengths 3&4 breathe every 5th stroke

Lengths 5&6 breathe every 7th stroke

Take as much recovery between sets as you need. Remember to trickle breathe throughout and DON’T hold your breath!

Matt Sanderson is a BTF Level 3 coach, NASM Performance Enhancement Specialist, Corrective Exercise Specialist, Sports Massage Therapist, Level 4 Personal Trainer and the co -founder of Triathlon Coaching UK (TCUK)



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