What Is Heart Rate Reserve?

Heart Rate Reserve (HRR) is the difference between your maximum heart rate and your resting heart rate:

HRR = Max HR - Resting HR

For example:

• Max HR: 185 bpm
• Resting HR: 55 bpm
• HRR: 185 - 55 = 130 beats

This "reserve" represents your available heart rate range for exercise.

Why HRR Zones Are More Accurate

Standard heart rate zones based on percentage of max HR treat everyone the same. But two runners with the same max HR but different resting heart rates have different fitness levels and should train at different intensities.

Example:

Runner	Max HR	Resting HR	Zone 2 (60-70% Max)	Zone 2 (60-70% HRR)
A	180	45	108-126	126-140
B	180	65	108-126	134-146

Runner A (lower resting HR = fitter) can actually train at higher absolute heart rates for the same relative effort.

The Karvonen Formula

To calculate target heart rate using HRR:

Target HR = (HRR × % intensity) + Resting HR

Example for Zone 2 (60-70% intensity):

• HRR: 130 beats
• Resting HR: 55 bpm
• Lower bound: (130 × 0.60) + 55 = 133 bpm
• Upper bound: (130 × 0.70) + 55 = 146 bpm

Heart Rate Training Zones (Karvonen Method)

Zone	% of HRR	Purpose	Feel
Zone 1	50-60%	Recovery	Very easy, can hold conversation
Zone 2	60-70%	Aerobic base	Easy, conversational
Zone 3	70-80%	Tempo/Moderate	Harder conversation
Zone 4	80-90%	Threshold	Short phrases only
Zone 5	90-100%	VO2max	Can't talk

How to Measure Your Heart Rates

Resting Heart Rate

For accuracy, measure first thing in the morning:

1. Wake up naturally (no alarm if possible)
2. Lie still for 1-2 minutes
3. Measure using chest strap, watch, or manually
4. Record for 5-7 days
5. Average the values (discard unusually high readings)

Good practice: Track resting HR over time. Elevated resting HR can indicate:

• Inadequate recovery
• Oncoming illness
• Overtraining
• Dehydration

Maximum Heart Rate

The most accurate method is a max HR test:

Field Test Protocol:

1. Warm up thoroughly (15-20 minutes easy)
2. Find a hill (4-6% grade)
3. Run hard for 2-3 minutes up the hill
4. Jog back down
5. Repeat 3-4 times, going harder each time
6. On final rep, sprint the last 30 seconds
7. Highest HR recorded ≈ your max HR

Important:

• This test is extremely hard
• Don't attempt if you have heart conditions
• Consider doing with a partner or coach
• May need multiple attempts to find true max

Age-Based Estimation

If you can't test, use the formula (less accurate):

Traditional formula: Max HR = 220 - age

Tanaka formula (more accurate): Max HR = 208 - (0.7 × age)

For example (age 40):

• Traditional: 220 - 40 = 180 bpm
• Tanaka: 208 - (0.7 × 40) = 180 bpm

Note: Individual variation can be ±10-15 bpm from formulas. Testing is better.

Using HRR Zones in Training

Easy Runs / Recovery

Target: Zone 1-2 (50-70% HRR)

Keep easy runs easy. If you're creeping into Zone 3, slow down. The purpose is recovery and aerobic development—not fitness building through intensity.

Long Runs

Target: Zone 2, possibly Zone 3 late (60-75% HRR)

Start at the low end. It's normal for heart rate to drift upward (cardiac drift) during long runs due to dehydration and fatigue. If you start in Zone 3, you'll finish in Zone 4.

Tempo / Threshold Runs

Target: Zone 4 (80-90% HRR)

This should feel "comfortably hard." You can sustain it for 20-60 minutes depending on fitness. If you can't hold a conversation at all, you're too high. If you can chat easily, too low.

Intervals / VO2max Work

Target: Zone 5 during efforts (90-100% HRR)

Hard intervals should push you near your max HR. Recovery intervals should drop you back to Zone 1-2 before the next rep.

Common Mistakes

Mistake 1: Using Inaccurate Max HR

If your max HR is wrong, all your zones are wrong. A 10-bpm error in max HR significantly shifts your training zones.

Fix: Test your actual max HR rather than using formulas.

Mistake 2: Ignoring Resting HR Changes

Resting HR changes with fitness, fatigue, and health. Zones based on old resting HR may no longer be accurate.

Fix: Re-measure resting HR every few months, especially after fitness improvements.

Mistake 3: Obsessing Over Exact Numbers

Heart rate varies based on:

• Temperature and humidity
• Caffeine intake
• Sleep quality
• Stress
• Time of day
• Hydration

Don't stress if you're 2-3 bpm outside your target zone.

Fix: Use zones as guides, not rigid rules. Combine with perceived effort.

Mistake 4: Starting Too High on Long Runs

Starting a long run in Zone 3 because "Zone 2 feels too slow" leads to finishing in Zone 4-5, excessive fatigue, and poor recovery.

Fix: Start slower than you think you should. Heart rate will rise naturally.

HRR vs. % of Max HR: Which Is Better?

Heart Rate Reserve (Karvonen) advantages:

• Accounts for individual fitness (via resting HR)
• More accurate for well-trained runners
• Better reflects true effort levels

% of Max HR advantages:

• Simpler to calculate
• Doesn't require knowing resting HR
• Good enough for many recreational runners

Recommendation: If you track your resting HR, use HRR. If not, % of Max HR works fine.

Tracking Heart Rate Over Time

What Improving Fitness Looks Like

Resting HR decreases:

• Your heart becomes more efficient
• Each beat pumps more blood
• Fewer beats needed at rest

Same pace, lower HR:

• Runs that used to be Zone 3 become Zone 2
• You can run faster in the same HR zone

Faster pace at same HR:

• Your aerobic system becomes more powerful
• You're fitter

Signs of Overtraining (via HR)

• Resting HR elevated by 5-10+ bpm
• HR higher than normal at same easy pace
• Slow HR recovery after hard efforts
• HR variability decreased

If you notice these signs, take extra rest days.

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Heart rate training adds valuable data to your running—but it's one tool among many. Use HRR zones to guide effort, but also listen to how your body feels. The best training combines objective data with subjective awareness.

Calculate your pace-based zones with the Pace Zone Calculator.