Heart rate zones

Heart rate zones are ranges of heart rate used to prescribe exercise intensity; ISSA sets them as percentages of maximum heart rate tied to a desired adaptation.^{1International Sports Sciences Association, Exercise Selection, Technique, and Training Instruction: Fast Track Study Guide, p. 17.} Its five-zone system uses zone 1 at 50 to 60% for warm-up and cooldown, zone 2 at 61 to 70% for light work, zone 3 at 71 to 80% for moderate work that builds aerobic endurance, zone 4 at 81 to 90% for hard, anaerobic work, and zone 5 at 91 to 100% for maximum effort.^{1International Sports Sciences Association, Exercise Selection, Technique, and Training Instruction: Fast Track Study Guide, p. 17.}

ACSM doesn’t recommend the common 220 minus age estimate of maximum heart rate because it can under- or overestimate the value.^{2Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 346.} Even population-specific equations carry errors of 10 to 15 beats per minute, so ACSM prefers a measured maximum.^{2Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 346.} Daniels tested one runner whose maximum was 148 at age 30 and 146 at 55, far from the formula’s predictions.^{3Daniels, Daniels’ Running Formula, 4th ed., p. 76.}

Why zone numbers differ

For bike training, USA Triathlon uses six zones based on functional threshold heart rate, with zone 2 at 81 to 89% of that value.^{4USA Triathlon, Complete Triathlon Guide, p. 86.} Viada describes systems with three to seven zones using different metrics, without universally agreed boundaries.^{5Viada, The Ultimate Hybrid Athlete, p. 133.},^{6Viada, The Ultimate Hybrid Athlete, p. 136.} The NSCA’s personal training text instead gives heart rate reserve targets of 40 to 89% for apparently healthy adults, with 30 to 39% as a possible starting point for extremely deconditioned clients.^{7Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 442.}

In practice

• Check which system and reference value a program, watch or app uses before comparing zones.^{5Viada, The Ultimate Hybrid Athlete, p. 133.}
• When calculating zones from heart rate reserve, add resting heart rate back after multiplying; otherwise the target is too low.^{8Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 443.}
• Heart rate shows how hard a client is working, not how fit they are or how fast they can go.^{4USA Triathlon, Complete Triathlon Guide, p. 86.}