Table 3.

Data items

1	Citation details: author(s), date, title, journal, volume, issues and pages
2	Study design and setting
3	Study aim/purpose
4	Participants: the age, sex and playing level of the soccer players and the number of participants in the study
5	Participant recruitment procedures utilised
6	Exposure: the method of performing a purposeful header
7	The factor that the study is investigating in relation to head acceleration
8	Outcomes: how head acceleration was measured and the resulting acceleration
9	Measurement of head acceleration during a purposeful header and the relationship of this measurement with the influencing factor assessed by the study. Linear acceleration (LA), rotational/angular acceleration (RA/AA) and rotational velocity (RV) were all outcomes of interest
10	Any data analysis methods including statistical techniques