The Championship side played seven games in 26 days last month, and face the league leaders Cardiff City tomorrow.
The Boro manager told Sky Sports News: "In the Championship it is relentless. We play every three days in the Championship for 10 months, it seems.
"You ask the same players to go and do it again every single week, which is why, particularly in the Championship, you pick up huge amounts of injuries, which we have had.
"Instinct takes over as a footballer. As a boy, you grew up playing practically every night, a game of football, so when you become a professional, it's not such a burden to play, play, play."
Middlesbrough are currently seventh in the league table, just outside the playoff places.