"challenging to maintain" is grammatically correct and can be used in written English.
It is often used to describe something that is difficult to keep up or sustain. Example: "As a single parent, juggling work and childcare can be challenging to maintain."
Several CEOs found it challenging to maintain the momentum of the early years.
This simple perception has huge practical consequence and is challenging to maintain impeccably.
Both of his homers Monday went to center field, and Beltran, a switch-hitter, said it was challenging to maintain his swing from each side of the plate.
But because gardens were intended to be horizontal, not vertical, and because water, left to its own devices, flows down, not sideways, they are challenging to maintain.
There were some consumers who did find adjustable-rate mortgages challenging to maintain, the association report showed: so-called "subprime" borrowers, who typically pay higher rates than those with excellent credit, had a delinquency rate of 12.02 percent.
*More principals find it challenging to maintain an adequate supply of effective teachers in urban schools (60% vs. 43% in suburban schools and 44% in rural schools) and in schools with two-thirds or more low-income students (58% vs. 37% in schools with one-third or fewer).
Some Southern Democrats, perennially challenged to maintain white support, have declined to endorse Mr. Obama, of Illinois.
On a hot summer day, for example, the body is challenged to maintain its normal temperature of 98.6 °F (37 °C).
All parties should be challenged to maintain them in their 2015 manifestos, as they did in 2010, and Labour should certainly stick by the policy.
WHEN Lorin Maazel takes the helm of the New York Philharmonic this week, he will be challenged to maintain the high standard of performance instilled by his predecessor, Kurt Masur.
