Heading in football. Part 1: Development of biomechanical methods to investigate head response

Abstract

Objectives: There has been growing controversy regarding long term effects of repeated low severity head impacts such as when heading a football. However, there are few scientific data substantiating these concerns in terms of the biomechanical head response to impact. The present study aimed to develop a research methodology to investigate the biomechanical response of human subjects during intentional heading and identify strategies for reducing head impact severity. Methods: A controlled laboratory study was carried out with seven active football players, aged 20-23 and of average stature and weight. The subjects were fitted with photographic targets for kinematic analysis and instrumented to measure head linear/angular accelerations and neck muscle activity. Balls were delivered at two speeds (6 m/s and 8 m/s) as the subjects executed several specific forward heading manoeuvres in the standing position. Heading speeds up to 11 m/s were seen when the head closing speed was considered. One subject demonstrating averaged flexion-extension muscle activity phased with head acceleration data and upper torso kinematics was used to validate a biofidelic 50th percentile human model with a detailed head and neck. The model was exercised under ball incoming speeds of 6-7 m/s with parameter variations including torso/head alignment, neck muscle tensing, and follow through. The model output was subsequently compared with additional laboratory tests with football players (n = 3). Additional heading scenarios were investigated including follow through, non-active ball impact, and noncontact events. Subject and model head responses were evaluated with peak linear and rotational accelerations and maximum incremental head impact power. Results: Modelling of neck muscle tensing predicted lower head accelerations and higher neck loads whereas volunteer head acceleration reductions were not consistent. Modelling of head-torso alignment predicted a modest reduction in volunteer head accelerations. Exaggerated follow through while heading reduced volunteer head accelerations modestly. Conclusion: Biomechanical methods were developed to measure head impact response. Changing the biomechanics of currently accepted heading techniques will have inconsistent benefits towards the reduction of head loading. Furthermore, mathematical modelling suggested an increased risk of neck loads with one alternative technique. No consistent recommendations can be made on the basis of the current study for altering heading techniques to reduce impact severity.

Heading in football. Part 2: Biomechanics of ball heading and head response

“…This simplification eased the manipulation of the torso and was justified by the locked torso shape observed in the subject tests. 8 Position and movement of the torso of the model replicated the kinematics of the representative subject ( fig 2). We also added several modelling elements to output specific data such as the location of anatomical landmarks and the angle of the head compared with the volunteer.…”

“…Adaptation or alteration of the remaining model characteristics would therefore not be required. Implementation of the model was based on the kinematic and neck muscle EMG data from an initial set of subject trials 8 (n = 7). We selected a single heading scenario (test code: LS2; see table 1, reference 8 for explanation of heading scenario codes) and representative test subject as a baseline for validation and implementation of the model since the kinematic and kinetic responses are dependent on an individual's technique and physical characteristics.…”

“…Part 1 of this series ''Development of biomechanical methods to investigate head response'' deals with the development of biomechanical measurement methodology and human subject trial results. 8 A complementary study of external factors influencing head response-that is, ball impacts, is presented in Part 3 ''Effect of ball properties on head response''. 9 The numerical model described in this paper was used for Part 3.…”

Foul 2050: thoughts on physical interaction in human-robot soccer

“…2b; I1, I6, I7) • One player falling on the other one who is lying on the ground (I4, I7) This particularly limits the robot's weight because kinetic energy is according to [22], [23] a (limited) indicator of head injury and is (not directly) related to chest injury. Therefore, the robot's weight has to be similar to the one of professional soccer players.…”

Kick it with elasticity: Safety and performance in human–robot soccer

“…4b) or during a header. These impacts require the limitiation of the robot's weight because kinetic energy is, according to [46,57], a (limited) indicator of head injury and is at least somewhat related to chest injury. Therefore, the robot's weight has to be similar to the one of professional soccer players.…”