When you are well trained 50 meters is not stressfull. During training in the swimming clubs we also did this kind of exercices. You are living in France ?The only sport that I practice is quite never on TV. I'm free diver but my house is two hours minimum from sea and 3 hours from ocean. So sometimes I go to the public swimming pool but guards don't like me when I swim 50m underwater without breathing...to stressful for us...