Date of Award

8-25-2022

Publication Type

Dissertation

Degree Name

Ph.D.

Department

Kinesiology

Keywords

Helmet Impact;Methodology;Sport Biomechanics;Video Analysis;Youth Football

Supervisor

David Andrews

Abstract

Video analysis has played a key role in studying the biomechanics of in-game helmet impacts in football, both descriptively and quantitatively. To date, this work has primarily focused on concussive impacts in National Football League games due to the availability of high-quality, multi-view video for assessment (e.g., broadcast footage). Research efforts aiming to understand helmet impact biomechanics of untelevised youth football populations (≤ 14 years) have mostly relied on sensor-driven data from instrumented helmets. A few studies have used a single-camera system; however, this limits the data that can be obtained. The purpose of this dissertation was to develop, validate and apply a multi-camera approach (adapted from Jadischke et al. (2020)) to assess the biomechanics of helmet impacts in youth football games using descriptive and quantitative video analysis techniques. The overall goal of this research was to contribute to athlete safety improvements and inform youth-specific helmet test standards and design. These objectives were accomplished in three empirical studies. Study 1 (Chapter 2) used a videogrammetry approach to quantify three-dimensional (3D) helmet velocities of 21 non-injurious helmet-to-ground (H2G) impact cases identified from three youth football games (game A: 9–12 years; games B and C: 13–14 years). Contact progressions of these cases mostly involved a body-to-body and body-to-ground contact, followed by a rear or side helmet strike with the ground. Resultant pre-impact velocities averaged 4.04 ± 1.24 m/s at an angle of -49.6° to the field. The average resultant impact-induced change in helmet velocity was 3.32 ± 1.14 m/s; the approximate time interval of the duration of H2G contact was 0.06 s. In Study 2 (Chapter 3), a descriptive video analysis of the mechanisms and situational factors associated with helmet impact cases from the three youth football games was performed. The multi-view game video was reviewed and parameters related to all cases of observed helmet impact (injury and non-injury) were documented. Overall, the majority of cases occurred during a rush play (67.4%) and were concentrated in the mid-field (81%). Helmet-to-ground contacts were most common (59.1%) and contact locations were predominantly distributed across the rear (upper) (28.7%) and side (upper) (27.8%) helmet regions. Tackling was the most frequent activity leading to helmet impact (41.1%). The aim of Study 3 (Chapter 4) was to confirm the validity of the videogrammetry approach for measuring 3D helmet impact velocities in football by determining the effect of camera angle, camera distance and impact speed. A series of slow (1.04 m = 4.52 m/s) and fast (1.83 m = 5.99 m/s) free fall drop tests were conducted using a helmeted anthropomorphic test device head and neck assembly to simulate H2G impacts within two different zones on a football field. Helmet motion was tracked using 3D motion analysis software across different camera view combinations (orthogonal, coincident, overhead, parallel) for each zone, and resulting helmet velocities were computed. In general, the results showed the effectiveness of several camera angles (except parallel) for measuring 3D helmet impact velocity; increased camera distance and impact speed did not appreciably influence video tracking accuracy. Lastly, Chapter 5 explored the methodological considerations (e.g., equipment, input/output parameters) of accurately conducting laboratory reconstructions of H2G impacts for youth football players.

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