Cardiovascular Science • 8 Min Read

Target Heart Rate Training Zones: The Karvonen Formula, Tanaka Equation & Zone 2 Fat Burning Science

Author: Exercise Physiology & Aerobic Conditioning • Published: August 2026 • Reviewed by: Certified Strength & Conditioning Specialist (CSCS)
Endurance runner monitoring target heart rate on sports smartwatch
favorite Physiological heart rate zones: Optimizing cardiovascular adaptation, VO2 max, and mitochondrial biogenesis Photo: Royalty-Free Unsplash

Whether training for a marathon or optimizing longevity, exercising at the correct cardiovascular intensity is paramount. While the obsolete "220 − Age" formula carries significant individual error, the Tanaka Equation combined with the Karvonen Heart Rate Reserve (HRR) method calculates precise beats-per-minute (BPM) boundaries across the 5 physiological training zones.

format_list_bulleted Table of Contents

  1. 1. Maximum Heart Rate: Tanaka vs Fox Equations
  2. 2. The Karvonen Formula (Heart Rate Reserve)
  3. 3. The 5 Physiological Heart Rate Training Zones
  4. 4. The Power of Zone 2: Mitochondrial Density & Fat Oxidation
  5. 5. Worked Example: 35-Year-Old Athlete with 60 BPM Resting Heart Rate

1. Maximum Heart Rate ($HR_{max}$): Tanaka vs Fox

The traditional Fox formula ($220 − \text{Age}$) substantially underestimates maximum heart rate in older athletes. Exercise physiologists recommend the Tanaka Equation (Tanaka et al., Journal of the American College of Cardiology):

Tanaka Formula: HRmax = 208 − (0.7 × Age)
Heart rate training zones breakdown table and physiological energy systems
Figure 1: The 5 zones transition from active aerobic recovery (Zone 1) to pure anaerobic glycolytic power (Zone 5). 5 HR Zones

2. The Karvonen Formula (Heart Rate Reserve)

The Karvonen formula accounts for an individual's Resting Heart Rate ($HR_{rest}$), making it far more personalized than simple percentage-of-$HR_{max}$ calculations:

HRR (Heart Rate Reserve) = HRmax − HRrest

Target Heart Rate (THR) = (HRR × Intensity %) + HRrest
Heart rate reserve physiological curve graph comparing rest to maximum exertion
Figure 2: Incorporating resting heart rate reflects athletic cardiovascular efficiency (e.g., lower resting pulses in trained runners). HRR Dynamics

3. The 5 Physiological Heart Rate Training Zones

Zone Intensity (% HRR) Physiological Focus Effort & Talk Test
Zone 1 (Recovery) 50% – 60% Active recovery, tissue warm-up Very light, effortless conversation
Zone 2 (Aerobic Base) 60% – 70% Mitochondrial density, max fat oxidation Comfortable, full sentence conversation
Zone 3 (Tempo / Aerobic) 70% – 80% Cardiovascular endurance & blood volume Moderate, short sentence conversation
Zone 4 (Threshold) 80% – 90% Lactate threshold clearance & speed endurance Hard, single-word responses
Zone 5 (VO2 Max) 90% – 100% Maximum oxygen uptake & peak power Maximal sprint, impossible to talk
Cyclist riding on open road performing low-intensity Zone 2 endurance base training
Figure 3: Elite endurance athletes spend approximately 80% of their total annual training volume in Zone 2 (polarised training model). Zone 2 Aerobic Base

4. The Power of Zone 2 Training

In Zone 2, your Type I slow-twitch muscle fibers utilize oxygen to oxidize fatty acids for fuel. This stimulates mitochondrial biogenesis and enhances cellular metabolic flexibility. Training too fast (drifting into Zone 3) shifts energy production to glycolytic pathways, elevating lactate and reducing aerobic fat burning.

5. Worked Example (Age 35, Resting HR 60 BPM)

• HRmax (Tanaka): 208 − (0.7 × 35) = 183.5 BPM
• Heart Rate Reserve (HRR): 183.5 − 60 = 123.5 BPM
• Zone 2 Target (60% - 70%):
  – Lower Bound (60%): (123.5 × 0.60) + 60 = 134 BPM
  – Upper Bound (70%): (123.5 × 0.70) + 60 = 146 BPM
• Zone 2 Training Range: 134 to 146 BPM.

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