If you're trying to do any kind of statistical analysis of Gio Reyna's career, there's only really one dataset that has a big enough sample size.
Since what seemed like a breakout season at age 17 in 2020-21 -- four goals, five assists across 23 Bundesliga starts for Borussia Dortmund -- he has barely played. In the four seasons since, he has made just 14 starts, scored 11 goals and assisted four more. He's played just over 4,000 league minutes for Dortmund, attempted 88 shots, created 77 chances, and tried to beat a player off the dribble 81 times.
In this season alone, 12 players have attempted more shots, one has created more chances, and 87 have taken on more defenders across Europe's Big Five top leagues. We basically have one-plus full seasons of professional soccer for Reyna, played across six calendar years.
And so, all we really know about Gio Reyna is that his parents needed to read "How to Raise an Adult: Break Free of the Overparenting Trap and Prepare Your Kids for Success" and that he's always injured.
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For the lack of game-play data, we do have a ton of injury data. Per the site Transfermarkt, Reyna has missed 498 days due to injury since his career began, for 17 different reasons: colds, illnesses, infections, strains and fissures of the fibula. There's a fantastic book coming out soon from former ESPN editor Henry Abbott, "Ballistic," about the new science of injury prevention. If anyone from Reyna's team is reading this, I would highly recommend reading that book, too.
But beyond that, I can provide no insight on how to fix Gio Reyna's body because I am not a doctor. However, some newly available data can shine a light on how all the injuries may have affected the way Reyna plays for his club and the U.S. men's national team. He's not only missing lots of games, but he's moving very differently on the field.