The Conconi-Test is a practical method, of defining your Lactate Threshold LT (as Heart Rate or Power Level at the anaeronic/aerobic threshold) under realistic circumstances. This can then be used to define your Training Zones.

The success of the test depends largely on the choice of a suitable route. Ideally it would be a covered velodrome. But: who has a covered velodrome at his disposal? Alternatively a flat, wind-protected loop of about 400 to 800 meters (1/4 to 1/2 mile) - from a tartan track to a parking lot everything would do. But it needs to be wind protected! A tartan track is very often an ideal - providing more rolling resistance which will deminish the influence of the wind and make for a more accurate Conconi-Test.

Testing Procedure: Do not change position during the whole ride (aerodynamic drag remains constant - best accomplished with an aero bar). Increase your speed at every lap by 2 km/h (or 40 watts if you ride with a power measuring instrument.) Your heart rate should be continuously recorded or taken at every lap and noted by an assistant. You start at an easy pace (HR 110-120). The test ends once you no longer able to hold a constant speed for a whole lap.

Plot heart rate over speed as a graph. Connect the points with a line. The point where the line bends corresponds to your LT. This is clearer to spot if the speed axis is expanded.
Here is help for the evaluation:

Download the Spreadsheet