To keep in repair
To maintain the pace
She was walking behind him, trying unsuccessfully to keep up with his long strides.
She tried to keep up with him, but her legs ached from the unfamiliar exercise.
She followed him for miles, trying to keep up with his long strides.
If she couldn't keep up she would likely get him killed.
"We can't keep up this schedule," Betsy sighed as we crossed into Connecticut.