Group atrophy of muscle fibres denotes:

Group atrophy denotes enlarged motor units where all the fibers in the group are reduced to the same size. This is typical of progressive denervation. Reduction in the size of muscle fibers with an accompanying enlargement of intact motor units (because of collateral reinnervation) and degenerative changes in some fibers are the main changes of denervation atrophy is called denervation atrophy. Ref: Ropper A.H., Samuels M.A. (2009). Chapter 45. Electrophysiologic and Laboratory Aids in the Diagnosis of Neuromuscular Disease. In A.H. Ropper, M.A. Samuels (Eds), Adams and Victor's Principles of Neurology, 9e.