Arsenal manager Arsene Wenger has revealed that Theo Walcott and Alex Oxlade-Chamberlain are brought in and out of his starting lineup in order to maintain their physical condition.
Walcott has made 14 starts in the Premier League this season but has only completed 90 minutes on three occasions since October 22, while 10 of Oxlade-Chamberlain's 21 appearances have come from the substitutes' bench.
However, Wenger has explained that his decisions are largely based on keeping both players fit as the club look to maintain a challenge in both the Premier League and Champions League.
The Frenchman told reporters: "They play in positions where physical demands are higher. Today you need to come up and down and be a danger going forward. You need to find the level, a good balance.
"Oxlade-Chamberlain is much more efficient going forward now, he can provide, he did on Saturday for Ozil, and he can score goals.
"We have a squad of 25 people and the physical demands are the most important in that position, more than being a central defender. The changes are more frequent because of that position."
Both players could feature when Arsenal face Everton at Goodison Park on Tuesday night.