The understanding of association football head collision mechanics is of interest in the context of increased neurodegenerative disease risk in ex-professional players. This study sought to measure and characterise micromechanical pressure wave propagation from football head collisions; a distinct energy transfer mechanism from, and occurring before the start of, macromechanical gross head kinematics. A surrogate head setup, instrumented with a hydrophone pressure sensor, was exposed to footballs travelling at match realistic velocities. Pressure waves emanating from the region of first contact were measured within the cranial cavity. Their mean peak-to-peak magnitudes were up to 31.0 kPa. Across a range of 20 footballs of different materials, constructions and assembly methods, all of which satisfied the Laws of the Game, a 9.1-fold difference in peak-to-peak pressure and 54.7-fold difference in energy transfer, was observed. A 5-fold increase in peak-to-peak pressure was observed for a 77% increase in ball inbound velocity. Hydrophilic leather ball types demonstrated up to 4.2-fold greater peak-to-peak pressures when tested in wet, compared to dry conditions. These data highlight that pressure wave energy transfer may be influenced by the materials and construction of the ball, with scope to affect this without requiring alteration to the game or its Laws. The influence of these pressure waves on acute and long-term brain health requires further exploration.
Phillips et al. (Mon,) studied this question.