(CNN) Former San Francisco 49ers quarterback Colin Kaepernick -- who became a lightning rod in 2016 when he refused to stand during the National Anthem to protest the police shootings of black men and other social injustices faced by African Americans -- recognized the three-year anniversary of his first pregame protest on social media Wednesday.
Kaepernick wrote on Twitter, "Today marks the three year anniversary of the first time I protested systemic oppression. I continue to work and stand with the people in our fight for liberation, despite those who are trying to erase the movement! The movement has always lived with the people!"
A video accompanying the tweet shows videos of African Americans being killed by police, including 12-year-old Tamir Rice. It also features Kaepernick talking about the purpose of his protest.
Kaepernick first protested before a home preseason game against the Houston Texans on August 14, 2016.
He has not played in the National Football League since the 2016 season, when he sparked controversy by sitting, then kneeling, before several 2016 NFL preseason and regular-season games
Last week, the athlete-turned-activist posted a 59-second video on his Twitter account of him working out to show that he's ready to play again.
In the video, the words: "Denied work for 889 days" flashed across the screen.
"5 a.m., five days a week, for three years. Still ready," said Kaepernick, who played for the 49ers for six years.
Kaepernick became a free agent in 2017. No team offered him a contract, and that October, he filed a grievance against the league, accusing team owners of colluding to keep him from being signed.
He and former teammate Eric Reid, who knelt with Kaepernick, settled their collusion grievances cases against the NFL in February.