IF
Intensity Factor
Intensity Factor (IF) is the ratio of Normalized Power to FTP, expressing how hard a ride was relative to your threshold. Learn how IF is calculated and used in training.
Quick Answer
IF — Intensity Factor (IF) is the ratio of your Normalized Power to your FTP, expressed as a decimal. An IF of 1.0 means you rode at your threshold; IF of 0.75 means 75% of threshold. IF is essential for calculating TSS and assessing ride difficulty.
What Does Intensity Factor Mean?
Intensity Factor normalizes how hard your ride was relative to your current fitness (FTP).
IF Formula:
IF = Normalized Power / FTP
Example:
- Normalized Power: 225W
- FTP: 250W
- IF = 225 / 250 = 0.90
This means the ride was equivalent to holding 90% of your threshold power steadily—a hard effort.
IF Ranges and Meanings
| IF Range | Intensity Level | RPE | Example Ride |
|---|---|---|---|
| < 0.55 | Very easy | 1-2 | Recovery spin |
| 0.55-0.75 | Easy/Endurance | 2-4 | Zone 2 ride |
| 0.75-0.85 | Moderate | 4-6 | Tempo training |
| 0.85-0.95 | Hard | 6-8 | Sweet spot session |
| 0.95-1.05 | Very hard | 8-9 | Threshold workout |
| 1.05-1.15 | Maximum | 9-10 | Short race |
| > 1.15 | All-out | 10 | Sprint/short TT |
IF for Different Events
Typical IF values for various cycling events:
| Event | Duration | Target IF |
|---|---|---|
| Century | 5-7 hours | 0.60-0.70 |
| Gran Fondo | 4-6 hours | 0.70-0.80 |
| Road race | 2-4 hours | 0.80-0.95 |
| Criterium | 45-60 min | 0.95-1.10 |
| Time trial (40km) | 50-60 min | 0.98-1.05 |
| Track pursuit | 4-5 min | 1.15-1.25 |
The shorter and more intense the event, the higher the IF.
How IF is Used
1. Training Stress Score
IF is a key component of TSS:
TSS = (Duration in hours) × (IF)² × 100
The IF is squared, making intensity disproportionately important for training stress.
Example - Two rides with same TSS:
- 1 hour @ IF 1.0 = TSS 100
- 4 hours @ IF 0.5 = TSS 100
The short, hard ride creates the same stress as the long, easy ride.
2. Pacing Races
IF helps set realistic pacing targets:
| Race Duration | Sustainable IF |
|---|---|
| 60 minutes | 0.95-1.02 |
| 2 hours | 0.85-0.95 |
| 4 hours | 0.75-0.85 |
| 6+ hours | 0.65-0.75 |
See our Cycling Pacing Strategy Guide.
3. Training Zone Verification
IF helps confirm you're training in the right zone:
| Target Zone | IF Range |
|---|---|
| Recovery | < 0.55 |
| Endurance (Zone 2) | 0.55-0.75 |
| Tempo | 0.75-0.87 |
| Sweet Spot | 0.88-0.94 |
| Threshold | 0.95-1.05 |
| VO2 Max | 1.06-1.20 |
IF vs Normalized Power
| Metric | What It Shows | Use Case |
|---|---|---|
| NP | Absolute watts (adjusted for variability) | Compare power between rides |
| IF | Relative intensity (% of FTP) | Compare how hard rides felt |
IF is more useful for assessing training because it accounts for your current fitness level. An IF of 0.85 is the same relative effort whether your FTP is 200W or 300W.
Tracking IF Over Time
Signs of Improvement
| Observation | Interpretation |
|---|---|
| Same ride, lower IF | FTP has increased |
| Same IF, faster time | Efficiency improved |
| Higher IF feels easier | Threshold has improved |
Signs of Fatigue/Overtraining
| Observation | Interpretation |
|---|---|
| Lower IF than expected | Fatigue affecting performance |
| Can't sustain normal IF | Possible overtraining |
| Same IF but higher RPE | Accumulated fatigue |
IF Distribution in Training
For optimal training distribution:
| IF Range | % of Weekly Training |
|---|---|
| < 0.75 | 80% (easy/endurance) |
| 0.75-0.95 | 10% (tempo/sweet spot) |
| > 0.95 | 10% (threshold/intervals) |
This follows the polarized training model that most elite athletes use.
Common Questions
Can IF be greater than 1.0?
Yes—for short efforts. During a 20-minute FTP test, your IF should be approximately 1.05-1.10 (since you multiply 20-min power by 0.95 to get FTP). Races under 60 minutes often have IF > 1.0.
Why is my IF lower than expected?
Common reasons:
- FTP is set too high (need retest)
- Significant coasting or downhills
- Recovery spin mixed into workout
- Fatigue reducing power output
How does IF relate to heart rate?
IF and heart rate don't always align:
- Early in ride: HR may lag behind IF
- Dehydrated/hot: HR rises faster than IF suggests
- Fresh: Can sustain higher IF at same HR
Power-based IF is more reliable than heart rate for intensity measurement.
Should I track IF for every ride?
Yes—IF is valuable for all rides because it contextualizes your training relative to your fitness. Use it alongside TSS to monitor training load and prevent overtraining.