I have asthma, but it didn;t stop me from dong sports and other heavy activities.

My secret was I found a breathing technique on my own, that whenever I had a symptom of asthma attacking me, I do these things:

1. Be calm,
2. Regulate my breathing at a regular volume and natural interval (I don't breath fast or inhale-exhale big)
3. breath through my nose.
4. have an imagination, that I inhale and exhale through the back of my throat-neck and that i pass the air there,
5. Using that imaginary throat-neck passage muscle to breath, not my chest or stomach.

I think I did this since elementary school.

Now, just now, after years, I try to search that breathing technique for those who have asthma but want to do exercise, although the exercise will induce their asthma.

It turns out that my breathing technique is called the "BUTEYKO METHOD"

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http://en.wikipedia.org/wiki/Buteyko_method

Nasal breathing

The Buteyko method emphasizes the importance of nasal breathing, which protects the airways by humidifying, warming, and cleaning the air entering the lungs. A majority of asthmatics have problems sleeping at night, and this is thought by Buteyko practitioners to be linked with poor posture or unconscious mouth-breathing. By keeping the nose clear and encouraging nasal breathing during the day, night-time symptoms can also improve. Strictly nasal breathing during physical exercise is another key element of the Buteyko method.
Reduced breathing exercises

The core Buteyko exercises involve breath control; consciously reducing either breathing rate or breathing volume. Many teachers refer to Buteyko as 'breathing retraining' and compare the method to learning to ride a bicycle. Once time has been spent practicing, the techniques become instinctive and the exercises are gradually phased out as the condition improves.
Buteyko uses a measurement called the Control Pause (CP), defined as the amount of time that an individual can comfortably hold breath after a normal exhalation. According to Buteyko teachers, with regular Buteyko reduced-breathing practice, asthmatics are expected to find that their CP gradually increases and their pulse rate decreases in parallel decreased asthma symptoms.
Relaxation

Dealing with asthma attacks is an important factor of Buteyko practice. The first feeling of an asthma attack is unsettling and can result in a short period of rapid breathing. By controlling this initial over-breathing phase, asthmatics can prevent a "vicious circle of over-breathing" from developing and spiraling into an asthma attack. This means that asthma attacks may be averted simply by breathing less.
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and Youtube video:
www.youtube.com/watch?v=hx-3dt9L72c

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trust me, it's good, although I just found out what my breathing technique was, it really helped me as I have never taken medication for my asthma since I leaned this breathing technique on my own.