In June 1974 he set a new European record of 8:18.4 minutes, which he improved to a then-national record of 8:18.0 at the 1974 European Championships where he won the bronze medal. He improved his (West) German record on two occasions in Stockholm, first to 8:16.2 minutes in July 1975 and finally to 8:14.05 minutes in July 1977. This result places him sixth on the German all-time performers list, behind Damian Kallabis, Hagen Melzer, Frank Baumgartl, Rainer Schwarz and Uwe Pflügner.[5]
Karst won five German national titles, in the years 1974-1977 and 1979.[6] He competed for the sports clubs SV Saar 05 Saarbrücken and USC Mainz during his active career.