I have a good 45 minute cardiovascular workout just before swimming. Although I’ve got my breath back when I go in I imagine my body is still depleted in some way?

What factors affect my (or anyone’s) ability to conduct sustained swimming under water? And what can I do to improve my performance? Is the change in performance more likely to be due to age or to the prior cardiovascular workout?


A little back ground

I’m now 57 and I do an hour’s cardio workout of quite vigorous intensity twice a week with heart rate up to 170 bpm for the last 5 years. I also play short tennis once a week and do a reasonable amount of walking. So I’m active and reasonably fit. In my early forties I was doing a desk job, didn’t go to the gym and was not that fit, but I was still able to swim a 25m length under water (just) most of the time that I really tried. Now I find that I can only do 20m before coming up for air. That said I swim after going to the gym so I’m not “fresh”, although my breathing has returned to normal when I’m in the pool.

I suppose what I should do is try the swimming first as a proper comparative test for myself, age v fitness. But this made me wonder what factors would affect my performance. Some things I have noticed are that hyperventilating (but not going to mad!) seems to help so perhaps not being fresh is important, as I have only ever been able to do the underwater length once per pool visit, but I’m not sure why?

Update - I am now able to swim this under water length without difficulty provided I spend 7 minutes breathing quickly before trying. Not enough to make me feel dizzy but the blood must be well oxygenated.

  • Nice question. Happens to all in underwater activities as they age. 20 m is good! Wrong place for the question. Something to do with iron deficiency so definitely a medical question. Oct 1, 2017 at 8:10
  • @gideonmarx Thanks, yes I wasn't sure where it belonged to begin with.I plan to try to swim the length fresh before the gym session at some point in the next few weeks, so I will report back.
    – Slarty
    Oct 1, 2017 at 13:28
  • Update 2019 January-September under water length attempt mostly twice a week everyone a success. Bad patch mid-September to mid-October only 50% success rate. Then 11 straight successes followed by 6 failures. Most recently 2 successes followed by 2 failures. I have changed from 2 to 3 gym sessions a week. Wonder if that’s the problem?
    – Slarty
    Dec 17, 2019 at 14:37

2 Answers 2


The main limitation here is that the oxygen you inhale before you submerge, is consumed by your muscles as you swim. The more energy you use, the faster your oxygen depletes, and this is what causes the "damn, I need to go up top and breathe again" feeling.

The best way to improve your underwater distances, is to learn the best techniques; that is to say, the technique that is most energy efficient.

Performance is expected to drop with age, but since you haven't told us your age, I wouldn't default to using that as an explanation. Where I swim, there are seniors who will out-swim me with a broken hip, simply because they know their shit.

If you have the opportunity, join a swimming class for intermediate/advanced swimmers, and they'll show you the ropes. Competetive swimmers rely heavily on having the most optimal technique in terms of each stroke's distance-to-oxygen-cost ratio, and they'll clear over half the length of the pool after the dive, with leg-drive only.

  • I have added some more details which might be relevant. You make some interesting points concerning swimming lessons. Although I am reasonable fit and I can swim my techneque is not good. Don't laugh but. I never learnt to front crawl so I swim on my back or breast stroke. Over half a length with leg drive only seems the way to go. In the next week or so I will try swimming before going into the gym to see what happens.
    – Slarty
    Sep 29, 2017 at 14:51
  • Knowing breast stroke, but not how to crawl, is actually the most common situation among adults. So there is absolutely nothing to be embarassed for. I was in the exact same boat before I decided to take lessons, because while my breast stroke was ok, I felt like I could shave whole minutes off my 500m by learning proper breast stroke, as well as crawl. And it did.
    – Alec
    Sep 29, 2017 at 15:24
  • But yeah, the breast stroke is something one can learn by watching someone. Crawling properly is a trained skill. If you go to a class, and explain you don't know how to crawl, half the class is thinking "ok good, it's not just me".
    – Alec
    Sep 29, 2017 at 15:28
  • Thx thats a relieff!
    – Slarty
    Sep 29, 2017 at 15:37
  • Well guess what, yesterday I managed a full 25m length underwater! Surprisingly that was also after my usual gym session. Not sure why, possibly down to slow accumulation of progress and a bit of luck, but somewhat bizarrely I tried again today fresh (no gym) and was 2-3m short.
    – Slarty
    Nov 15, 2017 at 16:31

Primarily lung capacity is the issue here, but the rate at which your body uses oxygen is determined by your overall fitness level, muscle mass and technical efficiency.

As a competitive swimmer with 30+ years experience, I know from experimenting that I can swim further/longer underwater by using a relaxed, steady pace (long, controlled breastroke pull and kick) than by trying to rush to the other end of the pool. This is because your body uses more oxygen when working harder.

Having more muscle mass is a big factor too. I like the analogy that bigger muscles is like having a bigger engine in your car: it goes faster but uses way more fuel. For your body during aerobic activity, fuel = oxygen (plus glycogen etc).

I would definitely try swimming first and compare the results. In some respects doing other cardio will have depleted your muscle energy stores which is likely to reduce your efficiency in the pool, but on the flip side it may improve oxygenation of your blood (which is why athletes warm up before competitions to "get the blood pumping"). Ideally perhaps do a short 10-15 minute cardio warm up and then get in the pool and see.

I will say that in terms of improving underwater endurance, really you need to keep practicing swimming, maybe using some breath control exercises like swimming front-crawl and only breathing every 5, 7 or 9 strokes instead of the more typical 3. Doing other cardio like running or cycling, while it helps with general fitness, won't necessarily improve your underwater endurance because this is actually anaerobic (without oxygen) ability, hence why training restricted breathing exercises will help more.

  • Some interesting points you make. I have now been attempting this under water length for more than 6 months and have achieved it 13 times, 3 in the last 2 weeks. I have found it vital to pre breathe for at least 5 mins and do some aerobic warm up first. I swim slowly near the bottom and allow myself to glide to a stop before the next stroke. Another very important factor is having a lowish heart rate and staying relaxed. I tried this in an outdoor pool on holiday in Fuerteventura in Feb but only got half way across. I suspect the low temperature was to blame (heart rate increased).
    – Slarty
    Apr 4, 2018 at 17:00
  • Good answer, +1, welcome to fitness.stackexchange.com
    – Eric
    Apr 4, 2018 at 17:58
  • I wouldn't recommend gliding to a stop - you will then use more energy fighting inertia to get moving again. Try keeping to a steady, rhythmic technique. Maximize the glide phase (being streamlined will help a lot - arms out straight beside your head, legs straight toes pointed down) but start the next stroke before you stop. Congrats on achieving it so much though, it isn't easy! Apr 5, 2018 at 8:39

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