Exercise Protocol
Exercises were performed in prone using a purpose built dynamometer (fig 1). Exercises were identical with respect to
relative load (20% of maximal voluntary contraction (MVC)), repetitions (3 repetitions), duration (60s duration), and rest
period between repetitions (30s rest period). The difference was the orientation of the craniocervical spine during the
performance of the exercise. In this manner, the exercises performed in this study comprised: (1) cervical extension in
craniocervical neutral (CCN) and (2) cervical extension in craniocervical extension (CCE). Cervical extension in CCN.
Participants were positioned prone with their head and neck in a neutral position so that the mass of the head was supported by resting the chin on the end of the plinth, which minimized activity of the cervical extensors between test repetitions (see fig 1 A).
The computer displaying the visual feedback of exercise intensity was positioned on the floor directly below their line of sight. The pad of the dynamometer was then lowered in contact with the external occipital protuberance. Participants were instructed to extend their neck by pushing the back of their head into the pad of the dynamometer.
A neutral craniocervical posture was encouraged by instructing the participant to maintain visual focus on the display graph immediately below them.
Cervical extension in CCE.
Participants performed the same exercise maneuver as for the CCN exercise with the exception that the head/neck orientation was maintained in 15° of CCE (as indicated by an inclinometer attached to the par-
ticipant’s head) for the duration of the exercise (see fig 1B).
The investigator manually assisted the participant into the correct degree of CCE immediately before the performance of
each repetition. Maintenance of the extended craniocervical orientation was encouraged by the participant maintaining focus on the visual display, which was now positioned forwardon the floor compared to its location during the CCN exercise
Procedure
Participants attended a preliminary session 48 hours prior to the experimental session in order to establish their MVC values for both exercise conditions. The order of testing was alternated between participants. Testing consisted of a standardized warm-up, followed by 3 MVC trials with a rest period of 60 seconds between trials. The maximum recording of the 3 MVC trials was used as the MVC score for the experimental session. A 5-minute rest period was allowed between MVC trials for the CCN and CCE conditions. During the experimental session, each participant first underwent final screening by a medical practitioner to ensure MRI suitability before undergoing the baseline (rest) MRI scans. Immediately after the baseline scan, each participant performed the first of the 2 isometric extension exercises (identical order to that performed during MVC trials) directly outside the magnet room. The second MRI scan was performed immediately after completion of the first exercise session. The participant then rested for a minimum of 45 minutes before performing the second extension exercise. Immediately after, they underwent the third and final MRI scan. A rest period of at least 45 minutes was required to allow for the baseline recovery of the shifts in T2 relaxation.
Accurate performance of the required 20% MVC effort during both exercises was ensured via real time visual feedback of the contraction effort displayed on the computer screen. Participants were encouraged to completely relax their neck
muscles during the rest periods between repetitions with their jaw and head supported on the padded edge of the bed.