Znamensky was born into a family of a priest and had four sisters and five brothers; one of them, Georgy, became his long-term training partner and rival in athletics.

Seraphim was trained as a musician by his mother; he was an accomplished singer and could read and write sheet music.

In those years the brothers trained by running 16 km between their home and the factory where they worked, while their diet consisted of rye bread, potato, and plenty of milk (a bucket per day for two).

Competing in various 1000 m – 10,000 m events, the brothers finished 18 times within the podium at the Soviet championships in 1934–1940 and set 24 national records.

At the onset of World War II in Russia they both volunteered as medical doctors to the Soviet Army.