Klodd E, Hansen A, Fatone S, Edwards M. Effects of prosthetic foot forefoot flexibility on gait of unilateral transtibial prosthesis users. J Rehabil Res Dev. 2010; 47(9):899–910. DOI:10.1682/JRRD.2009.10.0166

Figure 1. Hypothesized differences between prosthetic feet with different levels of flexibility at time of opposite initial contact: (a) prosthetic foot that allows long forward progression of ground reaction force (GRF) and (b) highly flexible prosthetic foot with limited forward progression of GRF. Effective foot length (EFL) of foot A is larger than that of foot B. “Ankle” flexion (Ø) range of motion for foot B is larger than for foot A. “Drop-off” in GRF is expected on overly flexible feet (such as foot B), leading to increased initial loading on sound limb and potentially reduced sound limb step length.