More older, middle-aged Americans are reporting serious mobility-related disabilities and difficulties performing activities of daily living than ever before, according to a new study.

Researchers at the RAND Corporation and the University of Michigan looked at responses to the “1997 to 2007 National Health Interview Survey,” and found a significant increase in the number of 50 to 64-year-olds with mobility issues. Roughly 40% reported having difficulties in at least one of nine physical functions measured by the survey, according to the report. They also noted a rise in the proportion of older middle-aged adults needing personal care assistance for back or neck problems, diabetes, and depression, anxiety or emotional problems.

The reasons for the trend are unknown, but the findings run counter to a decline in similar mobility issues among seniors aged 65 and older, according to researchers. While overall, only 2% of people in the 50 to 64-year-old age group do require personal care help, the significant increase “does not bode well for future trends for the 65 and older population,” according to lead author Linda Martin. The report appears in the April edition of Health Affairs.