Could and to be able to

We use could to talk about general abilty in the past and we use to be able to or managed to to talk about a specific situation in the past.


So we say

could run fast when I was a child.

because it is a general fact, but we say

was able to run five miles without stopping last night.
managed to run five miles without stopping.

because we are talking about a specific time in the past.

Other examples

could play football well I was a boy.
Last night I managed to score four goals.

could study all night when I was a student.
wasn’t able to concentrate on my studies last night.