Fitness (42-Day GRIT): Your fitness level based on 42-day GRIT average. Higher = more trained.
Fatigue (7-Day GRIT): Your fatigue level based on 7-day GRIT average. Higher = more tired.
Form (Fitness - Fatigue): Fitness minus Fatigue. Positive = fresh/rested, Negative = fatigued.
Efficiency Factor (EF)
What: Watts per heartbeat (Power / Avg HR) Why: Shows how efficiently you produce power Goal: Track improvement over time - rising EF = getting fitter Requires power meter data (cycling or running)
Aerobic Decoupling
What: Compares 1st half vs 2nd half efficiency Thresholds:
• < 5% = Good endurance
• 5-10% = Moderate (need more base training)
• > 10% = Poor (dehydration or insufficient aerobic base) Measures cardiac drift during steady efforts
RPE/HR Coherence
What: Compares perceived effort vs heart rate intensity Mismatch warnings:
• Feels harder than HR = overtraining, illness, or poor recovery
• Feels easier than HR = good fitness or incorrect max HR Early warning system for overtraining
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Performance Management Chart
Fitness (CTL)
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42-day avg
Chronic Training Load (CTL)
Your overall fitness level
42-day exponential moving average of your daily training load (GRIT).
42-day GRIT average of your training load. Higher CTL = better fitness base. Takes weeks to build, slow to decay.
💡 Good CTL: 50-150 (recreational), 150-250 (competitive)
ATL (Acute Training Load) - Fatigue
7-day GRIT average of recent training. Higher ATL = more fatigued. Responds quickly to training changes.
💡 ATL spikes after hard training blocks, drops during recovery
TSB (Training Stress Balance) - Form
CTL - ATL. Indicates your current freshness/fatigue state.
🟢 TSB > +5: Fresh, rested (good for racing)
🟡 TSB -10 to +5: Optimal training zone
🟠 TSB -30 to -10: Fatigued but productive
🔴 TSB < -30: Overreaching (risk of overtraining)
Training Load (GRIT)
GRIT Score: Your training load metric based on duration, intensity, and heart rate. Used to track fitness and fatigue.
💡 Higher GRIT = harder workout. Used for 7-day fatigue and 42-day fitness tracking
Advanced Metrics Guide
📊 TSS (Training Stress Score)
Power-based training load metric. Requires power meter and FTP setting.
• < 150: Light training session
• 150-300: Moderate workout
• 300-450: High load
• > 450: Very demanding
Formula: (duration × NP × IF) / FTP × 100
⚡ Normalized Power (NP)
Accounts for power variability (intervals, surges). More accurate than average power for non-steady rides.
Uses 30-second rolling average raised to 4th power
🎯 Intensity Factor (IF)
NP / FTP ratio. Shows workout intensity as percentage of FTP.
• 0.50-0.75: Recovery/endurance
• 0.75-0.85: Tempo
• 0.85-0.95: Threshold
• 0.95-1.05: VO2max
• > 1.05: Anaerobic
📈 Variability Index (VI)
NP / Average Power. Measures pacing consistency.
• 1.00-1.05: Steady pacing (ideal for TT, Ironman)
• 1.05-1.10: Moderately variable (crits, group rides)
• > 1.10: Highly variable (intervals, climbs)
⚙️ Efficiency Factor (EF)
Power output per heartbeat (W/bpm). Higher = more efficient. Tracks aerobic fitness improvements.
💔 Aerobic Decoupling
Compares first half vs second half efficiency. Detects cardiac drift (heart rate rising while power stays same).
• < 5%: Good endurance
• 5-10%: Moderate drift
• > 10%: Poor endurance (need more base training)
💡 To get these metrics:
1. Set your FTP in Settings (for TSS)
2. Use a power meter for cycling activities
3. Wear HR monitor for all workouts
4. Metrics appear automatically on sync