What functional threshold power estimates
Functional threshold power, or FTP, is commonly defined as the highest power a cyclist can sustain in a quasi-steady state for about an hour. It is widely used to set training zones. Because a true one-hour maximal effort is hard to execute and demoralizing to repeat, several shorter field tests estimate it instead.
The classic 20-minute test takes the average power over an all-out 20-minute effort and multiplies by roughly 0.95 to approximate the one-hour figure. The 8-minute protocol uses two 8-minute efforts with a larger correction. Ramp tests increase power in steps until failure and estimate FTP as a percentage (often around 75 percent) of the final completed minute's power.
Choosing and interpreting a protocol
The percentages are population averages and individual physiology varies, so FTP from a ramp test and from a 20-minute test can differ for the same rider. Consistency matters more than the exact protocol: retest the same way to track change. This is general training information and not medical advice; anyone with a cardiovascular condition should consult a clinician before maximal testing.