SEOUL (Reuters) - Fake casts for pretending you have an injured arm to evade having to help prepare holiday meals have become brisk sellers in South Korea ahead of the Chuseok festival.

"We have been selling this for 10 years now, but sales increased drastically starting last week," said a sales manager at an online vendor who declined to be identified.

Both men and women were buying the bogus casts, he said.

During Chuseok, a three-day thanksgiving holiday, women traditionally do most of the work in preparing and cooking elaborate ceremonial dishes while the men of the family chat, drink and watch television.

The holiday gender divide is so entrenched that it has spawned the term "daughter-in-law holiday syndrome", with many young women suffering post-holiday stress and fatigue.

But getting away with the phoney cast ruse may be difficult this year after several media outlets reported on brisk sales of the devices in the run-up to the holiday starting on Sunday.

Data from the Ministry of Gender, Equality, and Family in 2010 showed only 4.9 percent of people surveyed said both genders shared holiday chores, while the rest said women do most of the work.

"Although an increasing number of women are actively engaged in economic activities, a perception remains that only women are responsible for holiday preparation," said Na-Young Lee, a sociologist at Chung-Ang University.

"We need to try to understand that both men and women are equal beings in working and raising children in a family," she said.

(Reporting By Kahyun Yang; Editing by Tony Munroe and Robert Birsel)