Also, for any newbies burrowing through forums and wondering how exactly to calculate zones, this is what I found elsewhere on a forum/the UA site:
Zone 1
Heart Rate: AeT-20% to AeT-10%
Perceived Effort: Very easy to easy
Training Effect/Purpose: Aerobic conditioning
Metabolism: Aerobic-fat
Muscle Fiber Recruitment: ST
Training Method: Continuous 30 min to several hours
Zone 2
Heart Rate: AeT-10% to AeT
Perceived Effort: Moderate for those with high AeT, easy for those with low AeT
Training Effect/Purpose: Aerobic capacity, economy
Metabolism: Aerobic-fat dominates, maximum fat utilization
Muscle Fiber Recruitment: Most ST
Training Method: Continuous 30–90 min
Zone 3
Heart Rate: AeT to Lactate Threshold
Perceived Effort: Medium, fun-hard not exhausting
Training Effect/Purpose: Aerobic capacity, anaerobic capacity, lactate shuttle, economy
Metabolism: Glycolytic/anaerobic begins to dominate
Muscle Fiber Recruitment: All ST + some FT
Training Method: Interval 10–20 min, continuous to 60 min
Zone 4
Heart Rate: Lactate Threshold to LT to maxHR
Perceived Effort: Hard, max sustainable
Training Effect/Purpose: Maximal aerobic power, strength/speed endurance, economy, technique
Metabolism: Both aerobic and anaerobic capacities maxed out
Muscle Fiber Recruitment: All ST + most FT
Training Method: Interval 30 sec–8 min “