Fig 1.
(A) Visual depiction of a corticospinal silent period (CSP). A silent period in the surface electromyography (EMG) follows the delivery of a TMS pulse when participants are voluntarily contracting hand muscles. The CSP duration is thought to reflect the extent of GABAergic inhibition in the corticospinal tract [23]. (B) Visual depiction of the Headings and Control groups. The ball was manually thrown from a 6m distance at a set speed of 39 km/h (measured using a velocity speed gun on every throw). The ball was thrown once every 30 sec for a total of 20 times. Participants either headed the ball (Headings; upper panel) or controlled the ball using their dominant lower limb (Control; lower panel), therefore preventing any head impacts. (C) Timeline of the protocol. First, participants filled out the Rivermead Post-Concussion Questionnaire and a total of 20 valid CSP trials were collected (10 trials at 80% of the maximum voluntary contraction (MVC) and 10 trials at 40% MVC). Subsequently, participants performed the headings or lower limb ball contacts. Finally, the Rivermead Post-Concussion Questionnaire was filled again and a total of 20 valid CSP trials were collected a second time (10 trials at 80% MVC and 10 trials at 40% MVC). The measures were collected in this specific order for every participant.
Fig 2.
(A) Mean change and (B) individual data of the normalised CSP duration, depicted as a percentage change from the Pre Measures. These results show that CSP duration lengthened similarly in both groups, suggesting that corticospinal inhibition increased regardless of whether head impacts from football headings were experienced. (C) Mean change and (D) individual data of the (non-normalised) CSP duration, depicted as values in milliseconds. This confirms that the results in (A) and (B) are not a by-product of normalising the CSP duration. (E) Headaches and (F) Dizziness symptoms, as evaluated with the RPQ. The Headings group showed greater headaches and dizziness symptoms after headings were performed as compared to the Control group. This indicates that symptoms of head impacts were experienced in the Headings, but not in the Control group. For panels (A), (C), (E), and (F), the mean ± 95% CIs are shown. Asterisks (*) denote significant differences.
Table 1.
Descriptive statistics of the CSP and CSE results.
Table 2.
Group’s characteristics and RPQ results.