Sheffield United boss Chris Wilder admits his players have struggled physically in the Premier League.
The Blades host Chelsea on Sunday.
Wilder said: "It's difficult because I don't think we're at the level that we should be. Late goals have been a problem all season. It was a difficult start to the season because of the timings. To change it midway through the season is really difficult, especially when you're in a three-game week.
"Physically, it blinds every other league in the world. I think the only thing close to it is the Bundesliga. We aren't making tactical substitutions, we aren't bringing on experienced players who can change the game - we're making physical changes. It's a circle that keeps revolving and keeps going."
The Blades are bottom of the table, but Wilder adds: "I've had to do it since I was a 16-year-old lad. There's people around, the coaching staff stick together. I've got a very experienced and talented coaching staff. It's not easy, we'd rather be winning games."