The riskiest corporate debtors in the U.S. aren't growing fastenough to pay down their borrowings, increasing the risk for bondinvestors at a time when valuations are already at about recordhighs.

That's the conclusion of Deutsche Bank AG, which estimates thatthe biggest jump in earnings in almost three years may be comingtoo late for speculative-grade borrowers as the amount of debt onbalance sheets climbs back to levels seen in early 2008 before thefinancial crisis. To make matters worse, their ability to makeinterest payments is about where it was in 2007, even as theFederal Reserve has held its benchmark rate close to zero.

“We expect the next restructuring cycle will be dominated bycompanies with good operations but not able to grow into theirbalance sheets or refinance maturing debt,” Kenneth Buckfire,president of New York-based restructuring firm Miller Buckfire& Co., said by email Tuesday.