Overview of the protocol.

(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.