Cardiac Drift

What is Cardiac Drift?

Cardiac drift is the percentage change in your heart rate during sustained exercise at constant effort.

When you exercise at a steady effort for a prolonged period, your heart rate tends to increase gradually even though your pace or power remains constant. This phenomenon is called cardiac drift.

The Formula

Cardiac Drift % = ((Avg HR 2nd half - Avg HR 1st half) / Avg HR 1st half) × 100

Example

40-minute steady run:

• First 20 minutes: Average HR = 140 bpm
• Second 20 minutes: Average HR = 148 bpm
• Cardiac Drift = (148-140)/140 × 100 = 5.7%

Why Does Cardiac Drift Matter?

Cardiac drift reveals important information about your current state:

1. Hydration Status

• Low drift (<5%): Well-hydrated
• High drift (>10%): Likely dehydrated
• Blood volume decreases when dehydrated, forcing your heart to beat faster to maintain cardiac output

2. Heat Adaptation

• Low drift: Well adapted to current conditions
• High drift: Struggling with heat/humidity
• Body diverts blood to skin for cooling, reducing available volume for muscles

3. Recovery State

• Low drift: Well rested and recovered
• High drift: Fatigued or under-recovered
• Tired body works harder to maintain same effort

4. Aerobic Fitness

• Low drift: Better aerobic fitness
• High drift: Lower fitness or overtraining
• Fit athletes maintain stable cardiovascular function longer

Quality Ratings Explained

Good Coach App categorizes your cardiac drift into three quality levels:

Drift %	Quality	What it Means
<5%	Excellent	Well-hydrated, good conditions, recovered. Everything is optimal!
5-10%	Acceptable	Normal for longer efforts. Slight fatigue or warm conditions.
>10%	Poor	Dehydration, heat stress, fatigue, or illness. Take action!

Examples

Excellent Drift (2.1%):

Morning easy run, cool weather, well-hydrated
First half: 138 bpm → Second half: 141 bpm

Acceptable Drift (7.3%):

Long run on warm day, moderate hydration
First half: 142 bpm → Second half: 152 bpm

Poor Drift (12.8%):

Hot afternoon run, inadequate hydration
First half: 145 bpm → Second half: 164 bpm

Understanding Negative Drift

Sometimes you'll see negative cardiac drift (HR decreases in second half). This is not an error!

What Negative Drift Means

Negative drift (-2.5%):

First half: 147 bpm → Second half: 143 bpm

Common causes:

• Starting too fast - HR settles as you find sustainable pace
• Cooling conditions - Weather cools during workout
• Excellent pacing - Staying relaxed and controlled throughout
• Very easy recovery run - HR naturally stabilizes after warmup

Interpretation:

• Usually a good sign - shows discipline and control
• Common in recovery runs and easy efforts
• Can indicate good pacing strategy

Which Workouts Work for Cardiac Drift?

Cardiac drift is calculated for steady-state endurance workouts across all endurance sports.

Sports Included

• Running
• Cycling (road, mountain, track)
• Rowing
• Swimming
• Cross-country skiing

Ideal Workout Characteristics

Duration:

• Minimum: 30 minutes total
• Need: 20+ minutes after warmup removal
• Best: 45-90 minutes

Effort:

• Steady, sustained effort
• Constant pace or power
• No intervals or surges

Examples of Good Workouts:

• Easy 60-minute run at conversational pace
• 90-minute Zone 2 cycling ride
• 45-minute steady rowing session
• Long swim at cruise pace
• 2-hour XC ski at comfortable effort

Workouts That Don't Work

Interval Training:

• Track workouts
• Fartlek sessions
• Hill repeats
• Any workout with hard/easy segments
• Will show: "Intervals detected"

Very Short Workouts:

• <30 minutes total duration
• Will show: "Too short"

Missing Heart Rate Data:

• Forgot HR monitor
• Device malfunction
• Will show: "Missing HR data"

How to Use Cardiac Drift

Day-to-Day Training Guidance

Before workout:

• Check previous run's drift
• If drift was high (>10%), focus on hydration today

During workout:

• Can't see drift live (calculated after)
• But notice if HR creeping up unusually fast
• Consider slowing down or increasing fluid intake

After workout:

• Review drift percentage
• Compare to your typical values
• Adjust hydration or recovery if needed

Weekly Patterns

Track your normal range:

Week 1: 3.2%, 4.1%, 2.8%, 5.6% → Average ~4%
Week 2: 8.4%, 9.2%, 11.3%, 7.8% → Average ~9%

High drift week = Time to assess:

• Are you hydrating enough?
• Is training load too high?
• Need more recovery?
• Weather unusually hot?

Seasonal Trends

Summer to Fall transition:

July (hot):     Average drift 7.2%
August (hot):   Average drift 6.8%
September (cooler): Average drift 4.1%
October (cool): Average drift 3.5%

Pattern: Drift decreases as you adapt to heat or conditions improve

Training block progression:

Week 1 (fresh):    Average drift 3.8%
Week 2:            Average drift 4.2%
Week 3 (tired):    Average drift 6.1%
Week 4 (recovery): Average drift 3.2%

Pattern: Drift increases with fatigue, decreases with recovery

Common Questions

Q: What's a "normal" cardiac drift for me?

A: Everyone is different! Your normal depends on:

• Fitness level: Fitter athletes often 2-6%
• Sport: Running typically higher than cycling
• Conditions: Hot weather increases drift
• Duration: Longer efforts show more drift

Action: Track your personal baseline over 4-6 weeks of similar workouts.

Q: Should I worry about high drift during a race?

A: Race drift is often higher and that's expected:

• Higher intensity = more drift
• Longer duration = more drift
• Competition stress = more drift

8-12% drift in a race can be normal even for fit athletes.

Q: My drift is always low (<2%). Is something wrong?

A: No! Consistently low drift is typically excellent:

• You're well-trained
• Good hydration habits
• Running in good conditions
• Excellent aerobic fitness

Only concern if combined with:

• Unusual fatigue
• Declining performance
• Other symptoms

Q: Can I use cardiac drift for training zones?

A: Not directly, but it informs training:

• Low drift = Can potentially handle more volume
• High drift = May need easier week or more recovery
• Increasing trend = Consider deload week

Q: Does cardiac drift work for interval workouts?

A: No. Intervals are excluded because:

• HR varies by design (hard to easy to hard)
• Can't compare first vs. second half
• Would give meaningless numbers

Use cardiac drift for steady efforts only.

Q: How quickly can cardiac drift improve?

Changes within:

• Days: Hydration, recovery, heat adaptation
• Weeks: Training adaptations, fitness improvements
• Months: Major aerobic fitness gains

Example timeline:

Week 1 (dehydrated):     Average 9.2%
Week 2 (hydrated):       Average 5.1% ← Rapid improvement
Month 3 (fitter):        Average 3.8% ← Training effect

Q: Should I compare my drift to other athletes?

A: No! Cardiac drift is highly individual:

• Different fitness levels
• Different training history
• Different physiology
• Different conditions

Only compare to your own baseline.

Practical Tips

1. Stay Hydrated

Before workout:

• Drink 400-600ml water 2-3 hours before
• Another 200-300ml 15-20 minutes before

During workout:

• 150-250ml every 15-20 minutes for runs >60 min
• More in hot conditions
• Don't wait until thirsty

After workout:

• Check drift - if high, hydrate more next time
• Rehydrate with 1.5× fluid lost (weigh before/after)

2. Monitor Environmental Conditions

Hot weather strategy:

• Expect 2-4% higher drift
• Start easier than usual
• Increase hydration
• Consider time of day (early morning vs. afternoon)

Track patterns:

• Morning runs: Lower drift
• Afternoon runs: Higher drift
• Indoor treadmill: Different from outdoor

3. Use Drift for Recovery Assessment

Weekly check:

• Do same easy run each week (e.g., Monday 45-min recovery)
• Compare drift values
• Rising trend = need more recovery

Example:

Week 1: 3.2%
Week 2: 4.1%
Week 3: 5.8%  ← Warning sign
Week 4: Take easier week
Week 5: 3.5%  ← Back to normal

4. Pre-Race Preparation

Race week:

• Monitor drift on easy runs
• Target: drift at or below your normal
• If elevated: prioritize hydration and rest

Race day:

• Accept higher drift during race (normal!)
• Use training drift as fitness indicator
• Well-adapted athletes handle race drift better

5. Long-Term Tracking

Monthly average:

• Calculate average drift for similar workouts
• Watch for trends (improving vs. declining)
• Correlate with performance and training load

Seasonal patterns:

• Note baseline for different seasons
• Summer: higher drift is normal
• Winter: lower drift is typical
• Spring/Fall: transitional periods

Real-World Examples

Example 1: Hot Weather Impact

Athlete: Recreational runner, moderate fitness

Cool morning (15°C):

• First half: 138 bpm
• Second half: 141 bpm
• Drift: 2.2% (Excellent)

Hot afternoon (32°C), same route, same pace:

• First half: 142 bpm
• Second half: 155 bpm
• Drift: 9.2% (Acceptable)

Lesson: Heat significantly impacts drift. This is normal and expected!

Example 2: Training Block Fatigue

Athlete: Competitive runner, high fitness

Fresh (Week 1):

• Easy run: 2.8% drift
• Long run: 4.1% drift

Mid-block (Week 3):

• Easy run: 5.2% drift
• Long run: 7.8% drift

Recovery week (Week 4):

• Easy run: 2.9% drift
• Long run: 3.8% drift

Lesson: Drift increases with fatigue, decreases with recovery. Use this to manage training load!

Example 3: Hydration Learning

Athlete: Marathon training, learning hydration strategy

Long run #1 (minimal hydration):

• Drift: 11.4% (Poor)
• Struggled in second half

Long run #2 (planned hydration):

• Drift: 5.8% (Acceptable)
• Felt much better

Long run #3 (optimized hydration):

• Drift: 4.2% (Excellent)
• Strong finish

Lesson: Proper hydration dramatically reduces drift and improves performance.

Quick Reference Guide

Interpretation Cheat Sheet

Your Drift	Status	Action
<3%	Optimal	Great! Maintain current approach
3-5%	Excellent	Normal for fit athletes, keep it up
5-7%	Good	Acceptable, monitor trends
7-10%	Borderline	Check hydration and recovery
10-12%	High	Review hydration, heat, fatigue
>12%	Very High	Take action - hydrate, rest, cool down

When to Take Action

Single high reading:

• Don't panic
• Review conditions (heat, hydration, sleep)
• Monitor next workout

Consistent high readings (3+ in a row):

• Increase hydration
• Add recovery days
• Reduce training intensity
• Check for illness

Steady upward trend:

• Sign of accumulating fatigue
• Plan recovery week
• Assess training load
• Prioritize sleep and nutrition

Summary

Cardiac drift is a valuable daily indicator that tells you:

• How well you're hydrated
• How adapted you are to conditions
• How recovered you are
• How your fitness is trending

Use it to:

• Adjust hydration strategy
• Monitor recovery status
• Guide training intensity
• Track fitness improvements

Remember:

• Lower drift = better (generally)
• Negative drift is usually good
• Compare only to yourself
• Trends matter more than single values
• It's one tool among many - use with other metrics

Key insight: Unlike metrics that change slowly (fitness, VO2max), cardiac drift responds quickly to hydration, heat, and recovery - making it perfect for day-to-day training adjustments!