The Problem With "Feel-Based" Training
Here's a scenario I see constantly: an athlete tells me they do "easy" runs three times a week. But when I look at their data, every single run is at 75-85% of max heart rate—solidly in the "tempo" zone.
They think they're building an aerobic base. In reality, they're accumulating fatigue, making minimal aerobic gains, and wondering why they plateau after a few months.
This is the problem with guessing your training intensity. What feels "easy" after a rest day feels very different from what feels "easy" after a hard week. Your perception lies. Your heart rate doesn't.
What Are Heart Rate Zones?
Heart rate zones are defined intensity ranges based on your maximum heart rate or threshold heart rate. Each zone produces different physiological adaptations:
Zone 1: Recovery (50-60% Max HR)
Feel: Very easy, could do it all day
Purpose: Active recovery, warm-ups, cool-downs
Adaptation: Promotes blood flow for recovery without adding training stress
Zone 2: Aerobic Base (60-70% Max HR)
Feel: Comfortable, conversational pace
Purpose: Building aerobic foundation
Adaptation: Increases mitochondria, improves fat utilisation, builds endurance
This is where 80% of your training should live.
Zone 3: Tempo (70-80% Max HR)
Feel: "Comfortably hard," can speak in short sentences
Purpose: Moderate endurance, race pace for longer events
Adaptation: Improves lactate clearance, muscular endurance
Often overused—the "grey zone" that provides moderate stress with moderate benefit.
Zone 4: Threshold (80-90% Max HR)
Feel: Hard, can only say a few words
Purpose: Raising lactate threshold
Adaptation: Increases the pace you can sustain for extended periods
Zone 5: VO2max (90-100% Max HR)
Feel: Very hard, maximum sustainable effort
Purpose: Improving maximal oxygen uptake
Adaptation: Increases cardiovascular capacity and top-end speed
The 80/20 Principle That Changes Everything
Research consistently shows that elite endurance athletes spend approximately 80% of their training time at low intensity (Zones 1-2) and only 20% at moderate-to-high intensity (Zones 3-5).
Most age-group athletes do the opposite—they spend too much time in the moderate "grey zone" and not enough time either truly easy or genuinely hard.
Why This Matters:
Too much Zone 3 training causes:
- Accumulated fatigue without proportional fitness gains
- Insufficient recovery for adaptation
- Plateau after initial improvements
- Increased injury risk
Polarised training (80/20) delivers:
- Better aerobic development
- Fresher legs for quality sessions
- Sustainable long-term progression
- Lower injury rates
How to Find Your Zones
You have several options:
Option 1: Age-Based Estimation
Max HR ≈ 208 - (0.7 × age)
For a 50-year-old: 208 - 35 = 173 bpm max HR
Limitation: Individual variation can be ±10-15 bpm
Option 2: Field Test
After a thorough warm-up, run a hard 20-minute time trial. Your average HR for the last 10 minutes approximates your Lactate Threshold HR. Set zones from there.
Option 3: Lab Testing
VO2max or lactate testing provides the most accurate zones but requires access to a sports science facility.
Free Tool: Heart Rate Zone Calculator
I've built a free calculator that determines your personalised zones using multiple methods. It even generates an AI prompt you can use for deeper analysis.
Practical Application: A Week in Zones
Here's how zone-based training looks in practice for an Olympic-distance triathlete:
Monday: Rest
No training stress. Let adaptation happen.
Tuesday: Run Intervals (Zone 4-5 Focus)
- 15min Zone 2 warm-up
- 5 x 4min Zone 4 with 2min Zone 1 recovery
- 10min Zone 1 cool-down
Workout breakdown: 60% Zone 1-2, 40% Zone 4-5
Wednesday: Bike Endurance (Zone 2)
- 75 minutes steady Zone 2
- Include 4 x 30sec high cadence (95-100rpm) in Zone 2
Workout breakdown: 100% Zone 1-2
Thursday: Swim Technique + Threshold
- 400m easy warm-up (Zone 1-2)
- 4 x 50m drills
- 5 x 200m at threshold pace, 20sec rest (Zone 4)
- 200m easy cool-down
Workout breakdown: 50% Zone 1-2, 50% Zone 4
Friday: Easy Run (Zone 2)
- 35 minutes strictly Zone 2
- If heart rate drifts up, slow down
Workout breakdown: 100% Zone 1-2
Saturday: Long Bike (Zone 2 with Tempo)
- 2.5 hours total
- First 90min Zone 2
- Middle 30min Zone 3 (race pace)
- Final 30min Zone 2
Workout breakdown: 80% Zone 1-2, 20% Zone 3
Sunday: Long Run (Zone 2)
- 75 minutes Zone 2
- Easy, conversational throughout
Workout breakdown: 100% Zone 1-2
Weekly Total: Approximately 82% Zone 1-2, 18% Zone 3-5 ✅
Using HRV to Fine-Tune Your Training
Heart Rate Variability (HRV) takes zone training to the next level by showing you when your body is ready for intensity and when it needs recovery.
What HRV Tells You:
- High HRV / Balanced status: Body is recovered, green light for intensity
- Low HRV / Unbalanced status: Accumulated stress, favour Zone 1-2 training
- Consistently declining HRV: Warning sign—consider a recovery day or week
My Personal Practice:
Every morning, I check my Garmin's HRV and Body Battery. If HRV is suppressed or Body Battery hasn't recovered to 70%+, I adjust the day's training—swap a threshold session for Zone 2, or take a complete rest day.
This approach has kept me racing competitively at 57 years old. Recovery isn't weakness—it's strategy.
👉 Learn more: Understanding and Using HRV for Triathletes
Common Mistakes When Training With Heart Rate
1. Not Accounting for Cardiac Drift
During long sessions, heart rate naturally rises even at constant effort (due to dehydration, heat, fatigue). Don't chase the same HR for 3 hours—pace yourself by feel in the second half of long sessions.
2. Using Running Zones on the Bike
Heart rate response differs by sport. Running typically produces 5-10 bpm higher HR than cycling at equivalent effort. Set sport-specific zones.
3. Ignoring External Factors
Caffeine, stress, heat, altitude, and sleep all affect heart rate. A "Zone 2" pace on a hot, humid day might push HR into Zone 3. Adjust accordingly.
4. Obsessing Over Every Beat
Don't stress if your HR spikes briefly on a hill. Look at average HR for intervals or sessions, not moment-to-moment fluctuations.
5. Never Testing
Your zones change as you get fitter. Retest every 6-8 weeks or when you notice that "easy" efforts feel easier at the same heart rate.
The Bottom Line
Training with heart rate zones transforms guesswork into precision. You'll know exactly when you're building aerobic base, when you're working threshold, and when you're recovering.
The result? Faster improvement, fewer injuries, and the confidence that every session is moving you toward race day goals.
Take Action Today
- Calculate your zones: Use my free Heart Rate Zone Calculator
- Monitor your recovery: Learn about HRV and what it means
- Get a structured plan: Check out my Training Plans with proper intensity distribution
- Want personal guidance?: Explore 1-on-1 Coaching
Questions about training with heart rate? Contact me—I'm here to help you train smarter, not just harder.