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The heart rate deflection point is a controversial way of establishing an athlete's anaerobic threshold. The anaerobic threshold is where the body starts to rely on producing energy anaerobically (literally without oxygen) rather than aerobically (literally without oxygen). The best way of measuring the anaerobic threshold is to take a blood sample and have it analyzed. This is obviously invasive, inconvenient, painful and somewhat expensive. In 1980, Italian sport scientist and medical doctor Francesco Conconi developed a test procedure for establishing an athlete anaerobic threshold based on heart rate. The idea behind the test is to have the athlete exercise of gradually increasing intensity while recording their heart rate. When the athlete starts to produce energy anaerobically, their heart rate will not go up proportionate to the intensity. This change from linear relationship between heart rate and intensity is called the [[Heart Rate ]] Deflection (HR_d).