Extrasystoles are a second contraction of the heart before it ejects blood.

Apparently, everyone has them now and then, just I really noticed them these couple days. My doctor was not very concerned, she only told me not to overwork and not to overdo it at sports. I told her my routine heart rates during training and she was not concerned at all.

I read somewhere on the 'net that training is actually beneficial (except with a screaming heart rate I guess ) and that both magnesium and potassium are important to prevent them.

I have been a good girl taking the magnesium. Funnily today was the first time I got really sweaty in class although I stayed well under 170! I am wondering if I have had too little for a long time... considering I was always practically sweat-less, nevertheless very thirsty during training - and I always only drank water (usually 1.5 liters). So I've probably lost enough magnesium the last couple weeks to make me "notice".

I am not worried anymore and I will just keep in mind taking it.