Arsenal boss Arsene Wenger has said he often substituted Alexandre Lacazette this season because the France striker was "a bit less sharp" toward the end of games.
Lacazette briefly became Arsenal's record signing when he joined from Lyon last summer, but has rarely completed 90 minutes in his debut season in England.
Wenger made a habit of taking him off for Olivier Giroud during the first half of the season, before January signing Pierre-Emerick Aubameyang became first-choice striker.
The manager said the frequent substitutions were down to a number of factors but felt the striker's levels dropped a bit later in games as he adjusted to the Premier League.
"I must say that he plays in a position where you sub more than, say, a defender," Wenger told the official Arsenal website.
"You substitute a striker more than you would a defender because they always have to provoke, to defend, to attack, you have to create holes in the defences.
"Secondly, he was in an adaptation period where I felt that, without any objective measurement, sometimes he struggled a bit more in the second part of the game, especially in the last 25 minutes, to create the movement he can create.
"I put that down to an adaptation period. It was not so much physically -- that didn't drop so much -- it just looked like he was a bit less sharp."
Wenger also discussed how modern fitness data can affect substitutions, with managers better able to predict which players may tire.
"We know the players' physical qualities and who we expect to drop in the second half or not," he said.
"Nobody's tired enough at half time to be substituted for that, but in the second half you'll see that sometimes this player will drop in the last 20 minutes.
"We have a fatigue factor coming in at different levels for everybody and we know the players who drop more in the second half than others.
"Some remain completely consistent and some even push upwards in the second half. There are players who drop up to 15 percent in the second half, so you have to consider that in your substitutions.
"Even if you do make substitutions, you always try to keep one free because you know this guy could need to be substituted as well so you need to keep a place for him."