Lewis Dunk felt Albion's exertions in beating Manchester City caught up with them against Arsenal.
Albion went down 2-0 at the Emirates in the final game of the season on Sunday and finished in 16th place on 41 points, the same total as last season.
“We weren’t good enough in the first half, maybe a little bit better second. That’s one of the only performances where we haven’t been at it this season and it’s frustrating,” said Dunk.
“The boys put a lot of effort into the game on Tuesday, but we weren’t at it on Sunday.”
Dunk acknowledged that a lack of goals was the main reason why they didn’t finish the season in a higher position.
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“We've created chances but not scored goals, that’s been the case this season and that’s why we were fighting against relegation,” he added.
“If we had found the back of the net more regularly, we might have been looking a lot further up the table.
“I think we deserved more over the course of the season, but you don't always get what you want. We’ll rest now and look to improve next season.”