Three Quebecers have lost an appeal of their conviction in connection with the extreme-sweating death of a woman who was wrapped in mud and cellophane at a spa.

The Quebec Court of Appeal's decision means Gabrielle Fréchette, Ginette Duclos and Gérald Fontaine will head to prison for the death of Chantal Lavigne.

Lavigne, 35, died in July 2011 after a sweating session organized by the accused.

Participants were plastered with mud, wrapped in a plastic sheet and a blanket and had their heads covered with cardboard boxes for nine hours.

A coroner described the process as the equivalent of being cooked alive.

The accused were found guilty in December 2014 of criminal negligence causing death and were sentenced in January 2016.