Limited biomechanical data exists concerning S-I head impacts. Eleven S-I head impacts of unembalmed cadavers were performed to study the mechanisms, tolerances, and responses involved. The 9.9 kg padded impactor at 6.8 to 10.2 m/s velocity produced cervical vertebrae fractures with no basal skull fracture. Peak forces over 5.7 kN, peak velocities over 7.5 m/s, and initial pulse work over 380 N⋅m began fracturing cervical vertebrae in anatomically normal subjects. The damage mechanism appeared to be compressive arching.