The Influence of Head Impact Threshold for Reporting Data in Contact and Collision Sports: Systematic Review and Original Data Analysis

BACKGROUND

Head impacts and resulting head accelerations cause concussive injuries. There is no standard for reporting head impact data in sports to enable comparison between studies.

OBJECTIVE

The aim was to outline methods for reporting head impact acceleration data in sport and the effect of the acceleration thresholds on the number of impacts reported.

METHODS

A systematic review of accelerometer systems utilised to report head impact data in sport was conducted. The effect of using different thresholds on a set of impact data from 38 amateur senior rugby players in New Zealand over a competition season was calculated.

RESULTS

Of the 52 studies identified, 42% reported impacts using a >10-g threshold, where g is the acceleration of gravity. Studies reported descriptive statistics as mean ± standard deviation, median, 25th to 75th interquartile range, and 95th percentile. Application of the varied impact thresholds to the New Zealand data set resulted in 20,687 impacts of >10 g, 11,459 (45% less) impacts of >15 g, and 4024 (81% less) impacts of >30 g.

DISCUSSION

Linear and angular raw data were most frequently reported. Metrics combining raw data may be more useful; however, validity of the metrics has not been adequately addressed for sport. Differing data collection methods and descriptive statistics for reporting head impacts in sports limit inter-study comparisons. Consensus on data analysis methods for sports impact assessment is needed, including thresholds. Based on the available data, the 10-g threshold is the most commonly reported impact threshold and should be reported as the median with 25th and 75th interquartile ranges as the data are non-normally distributed. Validation studies are required to determine the best threshold and metrics for impact acceleration data collection in sport.

CONCLUSION

Until in-field validation studies are completed, it is recommended that head impact data should be reported as median and interquartile ranges using the 10-g impact threshold.

The Influence of Optimal Handheld Load on the Technical Ability to Apply Ground Reaction Forces during Horizontal Jumping in Female Netball Players

Handheld load has been reported to enhance horizontal jump performance, however little is known about its influence on ground reaction forces (GRF), especially in female athletes. This study investigated the effects of individualized optimal handheld loading on the technical and physical ability to apply GRF during horizontal jumping in female netball players. Maximal effort, single standing, horizontal jumps were performed by 13 female netballers. Participants performed the jumps under 2 conditions: 1) unloaded, and 2) loaded. Eccentric mean horizontal GRF significantly increased with loading (p<0.05; Effect Size [ES]= 0.74). The ratio of horizontal-to-total GRF significantly increased (p<0.05; ES=0.57), however resultant GRF did not, suggesting that the technical ability to apply force in the direction of intended movement may be of greater importance than the magnitude of force applied. Jump distance also increased from 188.2±16.1 cm to 196.4±13.6 cm (p<0.01; ES=0.55) with handheld load. In conclusion, individualized optimal handheld loading improved single horizontal jump performance in this population of athletes; most likely through various mechanisms that allowed for increased eccentric horizontal GRFs and the technical ability of force application. Findings could have practical implications for the strength and conditioning coach, trainer and athlete.

Force-velocity profile: imbalance determination and effect on lower limb ballistic performance

This study sought to lend experimental support to the theoretical influence of force-velocity (F-v) mechanical profile on jumping performance independently from the effect of maximal power output (P max ). 48 high-level athletes (soccer players, sprinters, rugby players) performed maximal squat jumps with additional loads from 0 to 100% of body mass. During each jump, mean force, velocity and power output were obtained using a simple computation method based on flight time, and then used to determine individual linear F-v relationships and P max values. Actual and optimal F-v profiles were computed for each subject to quantify mechanical F-v imbalance. A multiple regression analysis showed, with a high-adjustment quality (r²=0.931, P<0.001, SEE=0.015 m), significant contributions of P max , F-v imbalance and lower limb extension range (h PO ) to explain interindividual differences in jumping performance (P<0.001) with positive regression coefficients for P max and h PO and a negative one for F-v imbalance. This experimentally supports that ballistic performance depends, in addition to P max , on the F-v profile of lower limbs. This adds support to the actual existence of an individual optimal F-v profile that maximizes jumping performance, a F-v imbalance being associated to a lower performance. These results have potential strong applications in the field of strength and conditioning.