"Is anyone else feeling rusty? #ISworeIdNeverBoomerang #forgiveme #hashtagstoo," Garner captioned the clip where she's wearing all black and kicking a mat that a trainer is holding.
Garner is no newbie to kickboxing. The actress showed off her impressive moves in the 2003 superhero film Daredevil and its 2005 spinoff, Elektra. She also kicked some serious butt as the star of the espionage thriller TV series Alias from 2001 to 2006.
Earlier this week, Garner and her estranged husband, Ben Affleck, were spotting catching up and co-parenting after Labor Day weekend. The couple has been vocal about putting their three children -- 11-year-old Violet, 8-year-old Seraphina and 5-year-old Samuel – first and looking out for their well-being.
Last month, the family celebrated Affleck's 45th birthday with a special dinner. See more of their celebration in the video below.