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The most common formula encountered is:
HRmax = 220 − age (caution: can vary significantly!)
This is attributed to various sources, often "Fox and Haskell". While the most common (and easy to remember and calculate), this particular formula is not considered by some to be a good predictor of HRmax.
A 2002 study [4] of 43 different formulae for HRmax (including the one above) concluded the following:
1) No "acceptable" formula currently existed, (they used the term "acceptable" to mean acceptable for both prediction of V_{\mathrm{O}_2 max}, and prescription of exercise training HR ranges)
2) The most accurate formula of those examined was:
HRmax = 205.8 − (0.685 * age)
This was found to have a Standard Deviation that, although large (6.4 bpm), was still deemed to be acceptable for the use of prescribing exercise training HR ranges.
This actually puts your maximum heart rate at 188.7
As per the links that I have put up earlier (and Abdulmajid (or Wardminter as he was previously known) doesn't like to read facts, he prefers his own opinion)
60-70% will help you burn more fat
70-80% will help your cardiovascular system.
80%-90% is the Anaerobic Zone - which can be beneficial if you are training hard and for competitions.
90-100% is the Red Line Zone and in this zone you will only be able to train for short periods of time. It effectively trains your fast twitch muscle fibres and helps to develop speed.
As with all of this, every one is individual and obviously as different levels of fitness.