Quantitative and qualitative analysis of head and body impacts in American 7v7 non-tackle football

Uncalibrated Single-Camera View Video Tracking of Head Impact Speeds Using Model-Based Image Matching

PURPOSE

This study evaluates the accuracy of a model-based image matching (MBIM) approach with model calibration for tracking head impact speeds in uncalibrated spaces from single-camera views.

METHODS

Two validation datasets were used. The first included 36 videos of guided NOCSAE headform drops at varying camera positions (heights, distances, camera angles) where a speed gate measured vertical impact speed. The second dataset had eight videos of participants performing ladder falls with marked helmets, captured using a 12-camera motion capture system to track head impact speeds. Each video was tracked frame-by-frame, matching a 3D NOCSAE headform model to the head using MBIM software. Accuracy was assessed by comparing captured to MBIM-tracked speeds by the mean difference and Root Mean Square Error (RMSE). A linear model assessed the influence of camera position.

RESULTS

For ideal camera views (90 degrees, height 1 or 1.4 m), MBIM-tracked vertical speeds were 0.04 ± 0.15 m/s faster than the true speed (RMSE 0.15 m/s; 2.3 ± 6.2% error). Across all 36 NOCSAE videos, MBIM-tracked vertical speeds were 0.03 ± 0.19 m/s faster (RMSE 0.19 m/s; 1.8 ± 6.9 % error). In participant videos, MBIM-tracked resultant speeds were 0.01 ± 0.33 m/s slower (RMES 0.31; 0.7 ± 9.5% error) compared to motion capture.

CONCLUSION

MBIM with model calibration can analyze head impact kinematics from single-camera footage without environment calibration, achieving reasonable accuracy compared to other systems. Analyzing head impact kinematics from uncalibrated single-camera footage presents significant opportunities for assessing previously untraceable videos.

Best Practices for Conducting Physical Reconstructions of Head Impacts in Sport

Physical reconstructions are a valuable methodology for quantifying head kinematics in sports impacts. By recreating the motion of human heads observed in video using instrumented test dummies in a laboratory, physical reconstructions allow for in-depth study of real-world head impacts using well-established surrogates such as the Hybrid III crash test dummy. The purpose of this paper is to review all aspects of the physical reconstruction methodology and discuss the advantages and limitations associated with different choices in case selection, study design, test surrogate, test apparatus, text matrix, instrumentation, and data processing. Physical reconstructions require significant resources to perform and are therefore typically limited to small sample sizes and a case series or case-control study design. Their accuracy may also be limited by a lack of dummy biofidelity. The accuracy, repeatability, and sensitivity of the reconstruction process can be characterized and improved by good laboratory practices and iterative testing. Because wearable sensors have their own limitations and are not available or practical for many sports, physical reconstructions will continue to provide a useful and complementary approach to measuring head acceleration in sport for the foreseeable future.

Three-dimensional video analysis of helmet-to-ground impacts in North American youth football

This study presents a video analysis of helmet-to-ground impacts in youth football (≤14 years). A total of 21 non-injurious helmet-to-ground impact cases were assessed from game video of two age divisions (9-12 years: n = 9; 13-14 years: n = 12) using a novel multi-camera videogrammetry approach. Descriptive parameters related to the game situation and impact mechanisms were documented. Motion analysis software was used to manually track and compute three-dimensional helmet kinematics and uncertainty of the motion tracking analysis was assessed. Overall, the impact cases primarily followed a body-to-body, body-to-ground, helmet-to-ground contact progression. Impact locations on the helmet were mostly distributed across the rear and side helmet shell. The resultant pre-impact velocities for these cases averaged 4.04 ± 1.24 m/s at an angle of -49.6° to the ground. The average resultant impact-induced change in helmet velocity was 3.32 ± 1.14 m/s; the time interval associated with the duration of helmet-to-ground contact was approximately 0.06 s. The average maximum uncertainty (±) error of the position coordinates from the helmet tracking was 1.5 ± 0.3 cm. In summary, this video-based methodology can effectively be used to quantify helmet impact velocities and locations in youth football games. To date, the acquisition of such information has largely been limited to professional football game footage. Therefore, the data reported here may help inform the development of more representative assessment methods for youth-specific helmet test standards.

3D Biomechanics of Rugby Tackle Techniques to Inform Future Rugby Research Practice: a Systematic Review

BACKGROUND

The tackle is the most common in-play event in rugby union and rugby league (the rugby codes). It is also associated with the greatest propensity for injury and thus accounts for the most injuries in the sport. It is therefore of critical importance to accurately quantify how tackle technique alters injury risk using gold-standard methodology of three-dimensional motion (3D) capture.

OBJECTIVE

To examine the 3D motion capture methodology of rugby-style tackle techniques to provide recommendations to inform practice for future rugby code research and advance the knowledge of this field.

STUDY DESIGN

Systematic review.

METHODS

Articles published in English language, up to May 2020, were retrieved via nine online databases. All cross-sectional, correlational, observational, and cohort study designs using 3D motion capture of tackle techniques in rugby code players met inclusion criteria for this review. A qualitative synthesis using thematic analysis was pre-specified to identify five key themes.

RESULTS

Seven articles met eligibility criteria. Participant demographic information (theme one) involved a total of 92 rugby union players, ranging in skill level and playing experience. Experimental task design information (theme two) included one-on-one, front-on (n=5) or side-on (n=1) contact between a tackler and a ball carrier, or a tackler impacting a tackle bag or bump pad (n=3). 3D data collection (theme three) reported differing sampling frequencies and marker sets. 3D data reduction and analysis (theme four) procedures could be mostly replicated, but the definitions of temporal events, joint modelling and filtering varied between studies. Findings of the studies (theme five) showed that the one-on-one tackle technique can be altered (n=5) when tackle height, leg drive and/or tackle speed is modified. A study reported tackle coaching intervention.

CONCLUSIONS

This is the first review to evaluate 3D motion capture of rugby-style tackle technique research. A research framework was identified: (i) participant demographic information, (ii) experimental task design information, (iii) 3D motion capture data specifications, and (iv) 3D data reduction and analysis. Adherence of future 3D tackling research to these framework principles will provide critical scientific evidence to better inform injury reduction and performance practices in the rugby codes.

TRIAL REGISTRATION

The review was registered with PROSPERO (registration number CRD42018092312 ).

Emergency Department Visits From 2014 to 2018 for Head Injuries in Youth Non-Tackle Football Compared With Other Sports

Background

Non-tackle football (ie, flag, touch, 7v7) is purported to be a lower-risk alternative to tackle football, particularly in terms of head injuries. However, data on head injuries in non-tackle football are sparse, particularly among youth participants.

Purpose

To describe the epidemiology of  emergency department visits for head injuries due to non-tackle football among youth players in the United States and compare the data with basketball, soccer, and tackle football.

Study Design

Descriptive epidemiology study.

Methods

Injury data from 2014 to 2018 were obtained from the National Electronic Injury Surveillance System database. Injury reports coded for patients aged 6 to 18 years and associated with basketball, football, or soccer were extracted. Data were filtered to include only injuries to the head region, specifically, the head, ear, eyeball, mouth, or face. Football injuries were manually assigned to "non-tackle" or "tackle" based on the injury narratives. Sports & Fitness Industry Association data were used to estimate annual sport participation and calculate annual injury rates per 100,000 participant-years.

Results

A total of 26,770 incident reports from 2014 to 2018 were analyzed. For head region injuries in non-tackle football, the head was the most commonly injured body part, followed by the face; the most common diagnosis was a laceration, followed by concussion and internal injury (defined as an unspecified head injury or internal head injury [eg, subdural hematoma or cerebral contusion]). The most common contacting object was another player. The projected national rate of head region injuries was lowest for non-tackle football across the 4 sports. In particular, the projected rate of injuries to the head for non-tackle football (78.0 per 100,000 participant-years) was less than one-fourth the rates for basketball (323.5 per 100,000 participant-years) and soccer (318.2 per 100,000 participant-years) and less than one-tenth the rate for tackle football (1478.6 per 100,000 participant-years).

Conclusion

Among youth in the United States aged 6 to 18 years who were treated in the emergency department for injuries related to playing non-tackle football, the most common diagnosis for injuries to the head region was a laceration, followed by a concussion. Head region injuries associated with non-tackle football occurred at a notably lower rate than basketball, soccer, or tackle football.

Quantitative and qualitative analysis of head and body impacts in American 7v7 non-tackle football

Objectives

Non-tackle American football is growing in popularity, and it has been proposed as a safer alternative for young athletes interested in American football. Little is known about the nature of head contact in the sport, which is necessary to inform the extent to which protective headgear is warranted. The objective of this study was to identify the location, types and frequency of head and body contacts in competitive 7v7 non-tackle American football.

Methods

Video analysis was used to document the type, frequency and mechanism of contacts across a series of under 12, under 14 and high school non-tackle tournament games. A subset of impacts was quantitatively analysed via 3-D model-based image matching to calculate the preimpact and postimpact speed of players’ heads and the change in resultant translational and rotational velocities.

Results

The incidence rate of head contact was found to be low (3.5 contacts per 1000 athlete-plays). Seventy-five per cent of head contacts were caused by a head-to-ground impact. No head-to-head contacts were identified. Most contacts occurred to the rear upper (occiput) or side upper (temporal/parietal) regions. Head-to-ground impact was associated with a maximum preimpact velocity of 5.9±2.2 m/s and a change in velocity of 3.0±1.1 m/s.

Conclusion

Non-tackle football appears to represent a lower contact alternative to tackle football. The distribution of head impact locations, mechanisms and energies found in the present study is different than what has been previously reported for tackle football. The existing tackle football standards are not appropriate to be applied to the sport of non-tackle football, and sport-specific head protection and headgear certification standards must be determined.