Work out your max heart rate: 220 - your age
x this by the desired target % expressed as a decimal
Example:
220 - 14 = 206
206 x 0.6 = 124 beats per min (bpm)
206 x 0.8 = 165 beats per min (bpm)
Therefore, to train in the Aerobic training zone your heart rate needs to be between 124 bpm and 165 bpm
60% - 80% is the Aerobic Training Zone (0.6 - 0.8)
80% - 90% is the Anaerobic (without oxygen) Training Zone (0.8 - 0.9)
90%+ Max Training Zone