Horizontal Jogging Meaning

(idiomatic, slang) sexual intercourse

Example: 1981 Punch, Volume 281, p506
  Sex in those days was regarded not so much as a playful sport, horizontal jogging it might be, as an unspeakable obsession needing pseudo-new assistance, the sin that dare not speak its name except in obscure, allusive, Latinate verbiage.
1984 Antony Jay & Jonathan Lynn, "Party Games," Yes, Minister, Season 3, Episode 8 (aired 17 December 1984), spoken by Sir Humphrey Appleby (Nigel Hawthorne).
  I think they refer to it as horizontal jogging.
1994 Michael Scott Rohan, The Gates of Noon, Avon Books, p32
  His sports were team games like football and basketball, not to mention horizontal jogging.