 Although prone "functional leg length" is a widely used chiropractic tool in their Activator technique, it is not a recognized anthropometric technique, since legs are usually of unequal length, and measurements in the prone position are not entirely valid estimates of standing X-ray differences.Measurements in the standing position are far more reliable.Another confounding factor is that simply moving the two legs held together and leaning them imperceptibly to one side or the other produces different results.