Cervical Strength, Proprioception and Performance in Adolescent Soccer

Primary outcomes

1. Cervical extension strength

   Time frame: baseline a year

   Cervical extension muscle strength will be assessed using a digital hand-held dynamometer (e.g., MicroFET2 or equivalent). Isometric cervical extension strength will be measured in a standardized seated position with the dynamometer placed on the occipital region. Participants will be instructed to perform a maximal voluntary isometric contraction against resistance for 5 seconds.

   Three trials will be recorded, and the highest value (in Newton, N) will be used for analysis. The outcome will be expressed as peak force (N).

2. Cervical flexion strength

   Time frame: baseline a year

   Cervical flexion muscle strength will be assessed using a digital hand-held dynamometer (e.g., MicroFET2 or equivalent). Isometric cervical flexion strength will be measured in a standardized supine position with the head in neutral alignment. The dynamometer will be placed on the frontal bone region. Participants will be instructed to perform a maximal voluntary isometric contraction against resistance for 5 seconds.

   Three trials will be performed, and the highest value will be recorded for analysis. The outcome will be expressed as peak isometric force in Newtons (N).

3. Proprioception analysis

   Time frame: baseline a year

   Cervical proprioception was assessed using a laser pointer system (Motion Guidance Clinic Kit, Motion Guidance LLC, Denver, CO, USA). The laser device was mounted on the participant's head, and participants were seated comfortably at a distance of 90 cm from the target. With the participant's eyes closed, the examiner positioned the head in the starting position and asked the participant to memorize this position. Participants then performed maximal right and left cervical rotation and returned to the starting position without guidance, verbally confirming when they perceived proper realignment. Each movement was repeated three times. The distance between the final position of the laser beam and the center of the target was measured, and the arithmetic mean of the three trials was recorded as the deviation distance (cm). To calculate the deviation angle, the arctangent formula (deviation distance / distance between the laser and the target) was used.