Power
CP (Critical Power)
The highest power you can sustain indefinitely from aerobic metabolism alone.
Critical Power (CP) is the highest power output that is sustainable through aerobic metabolism alone — theoretically forever, practically about 30–60 minutes for most athletes.
How it is calculated
CP comes from the same model as W'. Two maximal efforts of different durations give:
Power(t) = CP + W'/t
The 3-minute and 12-minute pairing is common because the durations bracket the heavy and severe intensity domains.
Why it matters
CP is often a better anchor than FTP for setting training intensities and modeling sustainable effort. Many coaches now prefer CP for athletes who do a lot of variable-power riding. Pair it with W' and you get a model that predicts real-world fatigue better than FTP alone.
Common misconceptions
- CP is not always equal to FTP, though they are usually within 5%.
- "Sustainable forever" is a theoretical asymptote, not a real ride duration.
- A 3-minute and 12-minute test pair must both be maximal — half-effort tests give garbage CP numbers.
Related concepts
W', FTP, TSS.