Jon Lester's 16-year Major League Baseball career has come to an end. 

Speaking to ESPN's Jesse Rogers, Lester explained his body isn't able to handle the grind of a full season anymore. 

"It's kind of run its course," Lester said. "It's getting harder for me physically. The little things that come up throughout the year turned into bigger things that hinder your performance."

Lester played for the Boston Red Sox, Chicago Cubs, Oakland Athletics, St. Louis Cardinals and Washington Nationals over the course of his career. He made five All-Star teams and had four top-10 finishes in Cy Young voting, including a career-best second-place showing in 2016. 

The Red Sox originally selected Lester in the second round of the 2002 MLB draft. He made his big-league debut in 2006, but his rookie season took a dramatic turn near the end of the year when he was diagnosed with a form of lymphoma after experiencing back pain. 

After undergoing chemotherapy treatment, Lester was able to return to the Red Sox late in the 2007 season. The Washington native made his first career playoff start in Game 4 of the 2007 World Series. He tossed 5.2 shutout innings in a 4-3 win to help the Red Sox sweep the series. 

Lester spent the first nine years of his career in Boston before being traded to the A's at the trade deadline in July 2014. He did help Oakland make the playoffs, but the team was eliminated with a memorable wild-card game loss to the Kansas City Royals. 

As a free agent that offseason, Lester became a key piece for the Cubs in their rebuild. He signed a six-year, $155 million deal with Chicago to reunite with Theo Epstein, who worked in Boston's front office from 2001-11. 

Lester was one of the Cubs' heroes during their run to the World Series in 2016. He went 3-1 in six appearances with a 2.02 ERA and 30 strikeouts in 35.2 innings. The left-hander pitched three innings in relief in Game 7 of the World Series against Cleveland on two days rest. 

That 2016 season also wound up being the last great year of Lester's career, though he did turn in an All-Star performance and a ninth-place finish in Cy Young voting two years later. 

Lester finished his career with the Nationals after being traded midway through the 2021 season by the Cardinals. 

All told, Lester went 200-117 with a 3.66 ERA and 2,488 strikeouts over 2,740 innings in 452 career appearances. He won three World Series titles and was named MVP of the 2016 NLCS after allowing just two runs in 13 innings over two starts against the Los Angeles Dodgers.