Three months ago I postulated that Jacoby Ellsbury of the Boston Red Sox became stronger due to rehabilitating his injury from the previous season. It appears the increase in strength did not abate. Jacoby started a power tear on July 20, and it continues through his current 18 game hitting streak. The following graph shows how his fly ball distance and slugging on those fly balls changed during the current season:
You could draw a very nice upward sloping line showing how Ellsbury's fly balls have pretty steadily carried farther throughout the year. Note that early in the season, the fly balls didn't carry as much, but his slugging percentage was still good as many of those fell for doubles. Starting on the 20th, he hit the tipping point where the long hits went a little further and started landing in the seats.
You can also see him getting stronger in his slugging heat maps (all balls in play):
He's expanded the area where he drives the ball. Whatever exercises he's doing, the whole Red Sox team should adopt them.