Friel Training Bible Zone	General Perception / Perceived Effort	Approx % of Max HR (varies among individuals)	Metabolic system
Z1	Easy	HR 50-65%	Easy aerobic
Z2	Moderate	HR 65-80%	Aerobic
Z3	Moderate-hard	HR 75-85%	Aerobic-anaerobic crossover
Z4	Hard	HR 80-90%	Anaerobic
Z5a	Lactate Threshold –hard plus	HR 85-92%	Anaerobic
Z5b	Very hard	HR 85-95%	Anaerobic
Z5c	All out	HR 95-100%	Muscular

 

While your zones will stay the same relative to your heart rate, through systematic training over time you can increase your ability to go faster at a lower heart rate and effort level through adaptation to exercise and increased metabolic rate (including the ability to remove lactate).

 

Generally accepted ideas about HR training:

 

• Recovery exercise in Z1
• Do base work in Z2
• Avoid Z3 unless on your way up to Z4 or down to Z2, or told by your coach for a specific reason.
• Do longer intervals in Z4/5a
• Do shorter intervals in Z5a or b
• Avoid 5c unless you’re a sprinter

 

Your zones may vary on different days due to a variety of factors, it is advisable to train by your zone or perceived effort as opposed to a preconceived interval (ie, I should run 1 mile at -:-- and will no matter what).