Effectiveness of a Quick Release Dynamic Muscle-strengthening Program on Dynamic Stabilization of the Cervical Spine

The goal of this clinical trial is to learn if Quick Release dynamic strengthening of the cervical spine extensor muscles' reflex could improve dynamic stabilisation capacities of the cervical spine by reducing muscle activation delay in amateurs rugby players. The main questions it aims to answer are described as follows:

The primary outcome measure is the comparison between the intervention and control groups of the variation in activation delay of the cervical spine extensor muscles in milliseconds (ms) between the beginning and the end of the strengthening program. The activation delay in milliseconds corresponds to the time between the onset of impact application on the head and the onset of reactive muscle force production measured by the Cervistab© ergometer.

The secondary outcomes are also a comparison between the two groups of the variations from the beginning to the end of the strengthening program for the followings parameters, measured during with the Cervistab© machine:

* Reflex Force Production Rate (N/ms): slope of the force/time graph.
* Maximum Reactive Force (N): maximum force value produced within 300 ms following impact.
* In both intervention groups: measurement of the variation in head displacement (in mm) during quick release strengthening protocol.
* In each subgroup, 10 participants will be equipped with Instrumented Mouthguards. Researchers will compare the variation in workload measured by these mouthguards during Cervistab evaluations conducted before and after the training protocol.

Researchers will compare the intervention group to a distractor (control) arm to see if our training protocol has an impact on the activation delay.

Rugby authorities are seeking preventive measures to reduce cranio-cervical injuries. Literature suggests that early and strong contraction of cervical spine muscles could decrease this risk. The Quick Release principle, using maximal isometric contractions and non-impact disturbances, might improve the dynamic stabilization of the cervical spine. No study has yet evaluated the effect of muscle strengthening programs on this stabilization.

It is hypothesized that specific training of the cervical spine extensor muscles could reduce activation delay and increase reflexive force.

This study is a single-centre, controlled, randomised, and stratified based on activation delay.

It is an open study with blind evaluation. Randomization will be stratified based on the activation delay of the cervical spine extensor muscles into two sub-groups (slow and fast), measured during the Cervistab© test at the inclusion visit.

Researchers propose an open-label study with blind evaluation: The principal investigator, who will conduct the pre- and post-training protocol tests, will not be involved in the training protocol (conducted by the associated investigator) and will therefore not know which program the tested subject completed.

Both groups will undergo a foundational cervical muscle strengthening regimen, which includes classic isometric contraction strengthening (duration = 20 minutes) at the beginning of their training session.

The second part of each training session will depend on the group to which they have been randomised (also 20 minutes):

* Either 20 minutes of dynamic strengthening through Quick Release (tested arm)
* Or 20 minutes of decision-making aid with Stroboscopic Glasses (control arm with distractor)

Both groups will do 10 trainings of 40 minutes dispatched on one month.

Cervistab ergometer is a machine developped by the main investigator and engineers that records force (in newton) as a function of time. It delivers impacts over the head of the subject. Each subject puts himself in "scrum" position and take small impacts over the head and we can measure the reflex force production rate after the activation delay.

Distractor arm : The comparison group will have to do useful tasks for their rugby practice that does not have an impact on the primary outcome. Here, researchers will ask the comparison group to use stroboscopic glasses to train their decision skills in catching and throwing rugby balls. The stroboscopic glasses switch from bright to dark at a certain frequency and hence, reduce the amount of visual information.

Eligibility Criteria:
Inclusion Criteria:

* Aged 18 or older
* Possess a valid rugby practice licence

Non Inclusion Criteria :

* History of serious cervical trauma during his career with : Need for surgery (in case of arthrodesis at 2 or more levels) and/or Persistent after-effects (sensory or motor), any cervicobrachial symptomatology.
* History of epileptic disease
* Any concussion less than one month old
* Population with special legal protection: Pregnant or breast-feeding woman (L. 1121-5), subject deprived of liberty (art.L. 1121-6), minors L. 1121-7, patient unable to give consent (1121-8), protected adults L. 1121-8, not affiliated to a social security scheme (L1121-8-1), vulnerable persons (L.1122-2), exclusion period (Article L1121-12).
* Refusal of consent after information
* Participant not fluent in French and without a support person able to read.
* People who practice other contact sports.