Kinematics of four methods of stabbing: a preliminary study

Despite considerable research and development into stab-resistant clothing, no data exists which provides valid data for knife-body contact speeds which may be used to ensure that an appropriate and standard protection level is provided. Such data can only be obtained by a quantitative kinematic analysis of the stabbing movement. Two-dimensional video techniques (50 Hz) were used to record images of subjects (n = 10) performing each of four stabbing actions; Long Over (LO), Long Under (LU), Short Over (SO), Short Under (SU). Images were digitised from a minimum of ten frames pre-, to at least six frames post-blade entry. A two-way analysis of variance applied to selected kinematic parameters revealed significantly higher (P < 0.01) blade entry speeds for LO and LU as compared to SO and SU, respectively. This was due to the extra distance over which knife speed could be increased in the former conditions. Significantly greater shoulder joint angular velocities were found for LU and SU conditions, whilst for the elbow joint, conditions LO and SO were significantly greater (P = 0.000008). This suggests that the entry speeds during LO and SO are derived from a greater contribution from elbow extensor muscles, whilst those for LU and SU are derived from a greater contribution from the shoulder flexors. It was concluded that two separate kinematic strategies were employed by subjects, and that the maximum speed which may be generated during stabbing is influenced by the manner in which the knife is held.