In modern observations of human coitus efforts are made to measure heart rate during sexual excitement, climax, the resolution phase, etc. The first attempts to measure heart rate during sexual intercourse date back to 1896, when G. Kolb carried out a range of experiments in this area. In the 1930s E. P. Boas and E. F. Goldschmidt made similar observations and in 1950 G. Klumbies and H. Kleinsorge included heart rate, blood pressure and respiratory changes in their experiments.