CHAPTER 5
Players 4 and 9 were the youngest of the participants and had two of the highest PLA values (44.6 and 34.6 g’s). Their high PLA values could be seen as a relation of isometric neck strength and impact magnitude. The two youngest players may have registered two of the highest g force values due to the fact that they may have not been as physically developed as the older players on the team [8].
Players 1, 3, 12, and 13 were evaluated by their coaching staff as having
“excellent” heading form. Player 1 recorded maximum average PLA, PRA, and duration for the 20-yard stationary passing header, while recording maximum average PRV for the 10-yard running shooting header. Player 1 recorded minimum average PLA, PRA, PRV, and duration for the 5-yard stationary clearing header.
Likewise, player 12 recorded maximum average PLA and PRA for the 20-yard stationary passing header in addition to recording maximum average PRV for the 20-yard stationary passing header. Player 12 recorded minimum average PLA and duration for the 5-yard stationary clearing header and minimum average PRA and PRV for the 5-yard stationary passing header. Player 13 did not record maximum average PLA or PRA for the 20-yard stationary passing header, however her average PLA, PRA, and PRV for the 20-yard stationary passing header were all within 15% of her maximum average values for PLA, PRA, and PRV. Player 13, like player 1, recorded minimum average PLA, PRA, PRV, and duration for the 5-yard stationary clearing header.
There appears to be a relative consistency of minimum average values for PLA, PRA, PRV, and duration for players considered to have “excellent” heading proficiency. This relative consistency could mean that when players are simply
trying to head the ball away without focusing on direction and accuracy the impact profiles are less severe than when asked to focus on accuracy and direction like in passing and shooting headers.
Players 14 was evaluated as having “poor” heading form. Player 14 recorded maximum average PLA, PRA, PRV, and duration for the 5-yard stationary passing header type. In fact, player 14’s values (PLA, PRA, PRV, duration) for the 5-yard stationary passing header were all at least 42% higher than the next highest magnitude header type values. This may provide evidence for a correlation between
“poor” heading form and impact severity profiles.
The xSposure scores must only be considered for the staged measurement day (data collection session 1) when analyzing inter-player values, because this was the only day when the players each performed the same amount of headers. In subsequent data collection sessions, players heading attempts were not kept constant because they were participating in a real game where minutes played and header amounts attempted varied. When comparing player heading proficiency and xSposure score, it is seen that the four players (1,3,12,13) with “excellent” heading form had 4 out of the 5 lowest xSposure scores and all below 155. In addition, the players (4,5,10) with “decent” heading form all scored within the higher half of xSposure scores and all above 200. In particular, player 4 scored the highest xSposure score of 346. Player 14, considered to have “poor” heading form, had an xSposure score of 193.
There does not appear to be a direct correlation between the number of impacts performed and xSposure score for the staged data collection day. However,
when broadly examining averages of the xSposure scores collected from all three data collection sessions, it can be seen that generally the more impacts taken the greater the xSposure score. The five players (2,9,11,13,14) with the least amount of recorded impacts had the five lowest xSposure scores, while the three of the five players (1,6,12) with the most recorded impacts had three of the 5 highest xSposure scores.
The impact locations are of particular interest when looked at in light of Ponce et al’s findings, which concluded that the forehead or frontal area of the cranium is the best, in terms of safety, place to head the ball [16]. The study does make note of the possible error in analyzing force impacts digitally by simulation due to the variability of real header types. The study also notes that the parietal zone is the worst part of the cranium to head the ball with. In examining Table 32, it is seen that players 1, 4, 6, and 12 headed at least 40% of their attempts, with impact profiles containing PLA in excess of 20g, with the front of their cranium.
Comparatively, the rest of the participants’ impacts that exceeded 20g had highest frequency locations of either the side (2, 3, 5, 7, 8, 10, 11, 13, 14) or the top (9) of their cranium. This is most likely a result of technique and is something that could be improved upon dramatically and easily within the high school women’s soccer population.
Limitations
Some real world logistic limitations were associated with this study. Not all participants (n=14) were present for all three data collection sessions. Additional testing days, particularly staged testing days, would have been beneficial to verify
and better correlate the results from data collection session 1. Ideally, the study would span the course of a season. This time frame would allow for more in depth analysis and ongoing recommendation of player form.
Additionally, it is important to note that the number of recorded impacts does not equal the number of attempted headers. Some header attempts by players may have been filtered out of the data as “clack” impacts. “Clack” impacts are those that the xPatch records as not real impacts based upon a proprietary algorithm designed by X2 Biosystems’ engineers. This may be a source of error in the study as some of the players attempted headers may have registered as clack and not been recorded. A new study that evaluates the accuracy of the xPatch’s clack measurement algorithm as it pertains to soccer headers may be useful future work, but is not within the scope of this study.
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