The inheritance of acquired characteristics is a hypothesis that physiological changes acquired over the life of an organism (such as the enlargement of a muscle through repeated use) may be transmitted to offspring. It is also commonly referred to as the theory of adaptation equated with the evolutionary theory of French naturalist Jean-Baptiste Lamarck known as Lamarckism.
I am sure that you know that you can't inherit your Dad's very large muscles. You may have the ability to enlarge them yourself but it will take a lot of work. You are not just born with them.
Mendel really disproved this with his work.