The Tigers were beaten 3-0 at St Andrew’s as they missed the opportunity to pull further away from the relegation zone and Adkins was disappointed with what he saw from his players.
“It’s a hard one to explain and I certainly didn’t see that performance coming,” said Adkins.
“Both teams had to deal with the conditions, and they dealt with them far better than we did. We gifted them the first goal, the second and third were probably a bit more fortunate for them, but Allan McGregor has had to make some really good saves – especially in the first half.
“Birmingham deserved to win the game because they were the better side on the day. They got the ball forward better than we did and we were on the back foot from the start.
“Allan kept us in the game for a long time and we didn’t perform to the level that we have been doing. That’s disappointing because we had a good following behind us.
“We knew it was going to be a tough game even though Birmingham had been on a poor run, but we were second best all over the pitch.
“It’s a shame after the players had done so well in the last two games.”