Triathlon Z2 Fat-Burning Training — Precise Determination of Z2 Pace for Swimming/Cycling/Running

Why Is Z2 Training the Cornerstone of Triathlon?

Z2 (Zone 2) corresponds to approximately 60-70% of VO2max, 65-78% of maximum heart rate, and a lactate concentration of 1.5-2 mmol/L. Characteristics of this intensity:

• Mitochondrial biogenesis: Low-intensity, long-duration training most effectively stimulates mitochondria
• Peak fat oxidation: FatMax typically falls in the middle of Z2
• High training volume accumulation: Fast recovery, low risk of overtraining
• Long-term adaptation: The foundation of the cardiovascular system

Four Methods for Determining Z2

Method 1: Heart Rate (Most Common but Least Accurate)

Karvonen Formula:

Z2 Heart Rate = Maximum Heart Rate × 0.65 ~ 0.78

However, heart rate is greatly affected by caffeine, sleep, temperature, and medication. It is recommended to combine it with other metrics.

Method 2: Power/Pace (Most Objective)

Based on individual FTP (cycling) or Threshold Pace (running):

Discipline	Z2 Intensity
Cycling	60-75% of FTP
Running	Threshold Pace + 60-90 sec/km
Swimming	CSS + 15-20 sec/100m

Method 3: Breathing Test (Most Practical)

Talk Test:

• Z1: Can sing
• Z2: Can speak in full sentences, but slightly breathless
• Z3: Can only speak in short phrases
• Z4: Can only say single words
• Z5: Cannot speak at all

Method 4: MAF Heart Rate Method

Phil Maffetone Formula:

MAF Heart Rate = 180 - Age

For example, a 35-year-old athlete has a MAF of 145 bpm. This is the upper limit for the aerobic base phase.

Detailed Z2 Pace for the Three Disciplines

Swimming Z2

Z2 determination in swimming is the most difficult because heart rate monitors are often inaccurate in the water. It is recommended to use CSS + pace differential:

CSS	Z2 Pace (CSS + 18 sec)
1:30/100m	1:48/100m
1:45/100m	2:03/100m
2:00/100m	2:18/100m

Perceived exertion: Can swim continuously for 30+ minutes, breathing every 3 strokes, without feeling breathless.

Cycling Z2

Z2 in cycling is the easiest to determine accurately because of the power meter:

FTP	Z2 Power (60-75% of FTP)
200W	120-150W
250W	150-188W
300W	180-225W

Perceived exertion: Can maintain 90+ cadence, can talk while riding, no heavy breathing needed.

Running Z2

Running Z2 is the most often neglected because most people’s “easy runs” are actually Z3.

Half Marathon PB	Z2 Pace
1:30	5:30-6:00/km
1:40	6:00-6:30/km
1:50	6:30-7:00/km
2:00	7:00-7:30/km

Perceived exertion: If you can maintain a cadence of 175+ while breathing through your nose, that is true Z2.

Accumulating Z2 Training Time

Base Phase Weekly Volume Recommendations

Level	Weekly Z2 Hours
Recreational finisher	6-8 hr
Advanced age-group	10-12 hr
Elite athlete	15-20 hr

80/20 Principle: 80% of total training volume below Z2, 20% above Z4. The Z3 in between should actually be minimized (it accumulates fatigue with low benefit).

Common Z2 Training Mistakes

Mistake 1: Running Too Fast

Most people’s “easy runs” are actually Z3. How to tell: Run for 30 minutes breathing through your nose and still be able to talk.

Mistake 2: Duration Too Short

Each Z2 session should last at least 45-60 minutes to trigger mitochondrial effects; sessions under 30 minutes have limited benefit.

Mistake 3: Ignoring Heart Rate Drift

During long Z2 sessions, heart rate naturally drifts +5-10bpm. This is normal; do not force the pace down.

Mistake 4: Z2 Every Day

Include at least 1-2 intensity sessions (Z4-Z5) per week; pure Z2 will lead to a plateau.

Z2 Training Effectiveness Indicators

Review these indicators after 6-8 weeks:

• Faster pace at the same heart rate (e.g., 5:30/km heart rate drops from 150 to 140)
• Resting heart rate drops by 5-10bpm
• HRV (Heart Rate Variability) improves
• AeT (Aerobic Threshold) power increases by 5-10%

Conclusion

Z2 training may seem “too easy,” but this is exactly the dividing line between endurance athletes and the general population. Spend 80% of your weekly time in Z2, and within six months you will find that your pace at all intensities has improved.

Related Reading

• Z2 Long-Distance Endurance Training: Power Range Settings and Long-Term Physiological Adaptations
• Cycling Aerobic Base Training: The Science and Practice of Zone 2 Heart Rate Training
• Triathlon Heart Rate Training: Managing Intensity Across Three Disciplines
• Zone 2 Running Training: Heart Rate Range and Perception for Low-Intensity Aerobics