I am a huge advocate of Swimsmooth. Not only does British Triathlon use their coaching methodology for the BTF coaching courses, Paul Newsome, owner, is a friend and my swim coach here in Perth. So I have poached much of this from Swimsmooth.
Having coached some newbie triathletes last night and focusing on exhalation and breathing it inspired me to put some notes into a blog as a reminder for all swimmers. Very few novice swimmers exhale properly into the water and all intermediate swimmers think they are exhaling correctly - at least, that's what they say when we ask them. Do they? Very few do. Even amongst advanced swimmers, quite a few like to hold onto their breath under the water.
Getting your exhalation right will make freestyle feel much easier, get you balanced in the water and as a bonus, make you more relaxed whilst swimming.
When you are swimming you should always be exhaling except when you turn your head to inhale.
You can exhale through your mouth or through your nose or through both, it doesn't matter. But when your face is in the water you should be exhaling all the time in one constant stream of bubbles.
Here are some reasons why it is important to exhale constantly
1) The most important reason is that when you hold your breath you tense up. When you breathe out you release that tension. Imagine you're having a stressful day and someone tells you to take a deep breath - it's not when you take the breath in that you feel better, it's when you let it go. Holding your breath tenses you up and that affects your swimming technique.
2) When you are holding your breath you can feel that you need to breathe. The sensation you are feeling is not the lack of oxygen, it's the build up of CO2. By holding your breath you are keeping the CO2 in your blood stream and lungs - this makes you feel desperate for air. Breathing out constantly while you swim feels much nicer - you get rid of the CO2 and no longer feel so desperate for air.
3) Having lungs full of air is bad for your body position - your chest is too buoyant. Since your body acts like a see saw around your centre, this causes your legs to sink in the water, creating extra drag.
4) Most swimmers try to exhale just before they turn their head to breathe - or even worse, try and exhale and inhale in the short window when their mouth is above the waterline! This is a really hard thing to do, each breath feels snatched and panicky. If you breathe late like this, the tendency is to lift your head to breathe to give yourself a bit more time. Lifting your head is bad swimming technique, it causes your legs to sink - adding lots of drag.
Have a look at this video which gives you some cues to 'bubble-bubble-breathe'