Intensity Factor (IF) in cycling: what it is and how to use it

Intensity Factor (IF) is the ratio of the Normalized Power (NP) of a ride to your Functional Threshold Power (FTP). One number that tells you how hard a workout really was, compared to your threshold.

The formula

It is one line:

IF = NP ÷ FTP

NP is a 30-second smoothed average power that weights hard efforts more than easy ones — the right number to use, not raw average. What FTP is and how to test it.

What the number means

• IF = 0.55–0.65: recovery ride. Easy spin, conversational.
• IF = 0.65–0.75: aerobic / endurance ride. Most of your base volume.
• IF = 0.75–0.85: tempo / sweet spot. Solid aerobic work.
• IF = 0.85–0.95: threshold. Hard, controlled.
• IF > 0.95: above threshold. Short efforts only.

A worked example

Your FTP is 250 W. You do a sweet-spot ride with NP of 215 W.

IF = 215 ÷ 250 = 0.86 — solid tempo work, sustainable for an hour or so.

Another day you race a 40-minute criterium. NP comes out at 280 W. IF = 280 ÷ 250 = 1.12 — a hard, above-threshold effort. You can read more about how that becomes a TSS score in our TSS guide.

IF alone is not enough

IF tells you how hard a workout was at any moment. To know what it cost your body, you also need duration — which is where TSS comes in. The short version:

• IF 0.70 for 90 min ≈ TSS 66 (moderate aerobic)
• IF 0.95 for 60 min ≈ TSS 90 (high threshold)
• IF 1.10 for 30 min ≈ TSS 60 (short but very hard)

Why IF is useful in practice

• Plan your week. Aim for an average IF around 0.70–0.75 across the week; keep a couple of days below 0.65 for recovery.
• Track progress. If your usual 1-hour ride starts feeling like IF 0.80 instead of 0.85, your FTP has probably gone up — time to retest.
• Avoid junk training. Riding every day at IF 0.75 turns the whole week into “medium”: too hard to recover, too easy to build top-end form.

TrainCurve scores it automatically

Every ride you upload gets NP, IF and TSS calculated from your raw power data — and rolled into your CTL, ATL and TSB so you can see whether the plan is working. Start free and watch your weekly IF and TSS in the dashboard.