I was always told the rule of thumb was "220 less your age" - until I
came across this formula today:

210 - (half age in years) - (0.11*(weight in kg)) + 4

That is amazingly close. The "traditional" 220-age has always given me a
heart rate too low.

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA