The phrase "a decline in abilities" is correct and usable in written English.
It can be used when discussing a reduction in someone's skills or competencies over time or due to certain circumstances.
Example: "After the injury, there was a noticeable decline in abilities that affected her performance in sports."
Alternatives: "a decrease in skills" or "a drop in capabilities."
"In the typical job -- especially in the service economy where people aren't constrained by their muscles -- we do not see a decline in ability at age 65".
There are concerns that admitting to a decline in ability and self-regulation, may become "red flags" and penalize them, resulting in loss of their driver's license.
Previous research discovered a decline in ability to perform ADL among individuals with heart failure during the first year after AMI [ 18].
It will progress to a decline in ability to understand other people's language.
The decline in charitable donations at the oldest ages was to a small extent mediated by a decline in cognitive abilities, as predicted by the cognitive ability hypothesis.
An explanation for this finding might be that age by itself represents an indicator of illness severity that bundles factors such as illness duration and number of episodes which might be related to a decline in cognitive abilities.
He is a very proud man and will want to show everyone that he is still a world-class player and dismiss any talk of a decline in his abilities.
As the disease advances, uncoordinated, jerky body movements become more apparent, along with a decline in mental abilities and behavioral symptoms.
He placed at the top of the first-class averages for the seventh successive season, although some critics detected a decline in his abilities.
Another problem for the archbishop was a decline in the abilities of the scribes at Canterbury, which is dramatically illustrated by the document, which has a number of errors and duplications.
