To further understand the role of the fibril surface in the observed behavior and the nature of the Proteinase K modification, we studied fibrils grown over extensive incubation periods. We employed a single standardization growth step followed by several shaving and growth steps, incubating the fibrils for 15 hours with monomer per shaving step. Post shaving, the long fibrils demonstrate a significantly enhanced elongation rate sustained increasingly as the fibrils have grown. During the final growth phase the accelerated growth is sustained for over 10 hours. DFanalysis of the growth phases reveals that, while some structural reorganization of the fibril matrix may occur in the early timepoints of the growth phases, the dominant source of added mass originates from amyloid fibril elongation (Fig. ). It is noticeable that the accelerated growth is additive, suggesting that the source of accelerated growth must be the fibril surface, rather than any structural modification of the fibril end.