Fascinating account of a modern movement begun by Paul Chanson promoting the Synergy concept in France and Belgium.

PDF of article in English.
Original article citation is: Sevegrand, Martine. “L’affaire Chanson (1950-1952): continence conjugale ou érotisme catholique?.” Revue d’histoire ecclésiastique 88, no. 2 (1993): 439. It is available on Proquest, but is behind a paywall.
Author’s summary

The publication at the end of 1949 of a book by Paul Chanson, a well-known Catholic intellectual, which sang the praises of “the reserved embrace” (Synergy), provoked a heated debate in the French Catholic world. The work was published by the Christian Marriage Association. It had a lengthy afterword by a professor of theology of the Dominican convent of Saulchoir. Chanson’s book divided the clergy and the laypeople preoccupied with morality within marriage. Thanks to abundant archival material, the article studies the controversy which lasted more than two years. It lasted until a Monitum of the Holy Office in June 1952. The case reveals both questions about sexuality and pleasure and the Church of Rome’s will to suffocate Catholic attempts to reconcile traditional morality within marriage with the physical enjoyment of spouses.

See also:

Art D’Aimer et Continence Conjugale by Paul Chanson (1949)

L’Étreinte Réservée: Témoignage des Époux by Paul Chanson (1951)

What if my family had known about Chanson’s “Reserved Embrace”?

Catholic Hierarchy Meets Synergy