From the Coach guide
A 30 min time trial that measures your threshold.
The test measures your threshold heart rate and pace. Coach sets your zones and your hard-day paces from the result.
Follow the steps on the session. Run the 30 min as hard as you can hold to the end. Run alone, on a flat route.
Coach finds the hard part by your pace. Your threshold heart rate is your average for its last 20 min.
Slow down, but keep running. Coach can read your threshold pace from 15 min or more of hard running. Your zones change only after the full 30 min with heart rate.
A test is the most direct measure of your threshold. Coach asks for one about every 8 weeks. Use the same route each time, so that the results compare.
Tempo run: comfortably hard, not all out. Race: other runners change your effort.
Coaching method
Friel's test is a 30-minute solo time trial. The average heart rate for its last 20 minutes estimates threshold heart rate.
It is a field method from coaching, not a lab measure of lactate. It works best run the same way each time.
Test–retest reliability study
Trained runners repeated a track field test within 2.0%, and within 1.3% once they knew the test. Coach counts a change between tests only when it is larger than that.
The study tested 10 trained men on a track. A road route with turns and wind varies more.
Coach