Comparative Effectiveness Randomised Controlled Trial of Hybrid Muscle Conditioning

Deep cervical flexor motor control exercise combined with upper trapezius endurance exercise (named as Hybrid group and serves as the experimental group for comparison of its effectiveness to the two single-exercise comparator groups)

Hybrid exercise programme included 1) deep cervical flexor motor-control and 2) upper trapezius endurance exercise for five consecutive weeks. The low-load craniocervical flexion exercise (for facilitation of the activation of longus capitis and longus colli) will be performed in supine crook lying position with the participants' head and neck in a neutral position. Training commences at the participant's baseline craniocervical flexion test endurance score (20mmHg to 30mmHg) for 10 repetiation of 10-second hold time using the pressure biofeedback unit, under the supervision by a physiotherapist, who is independent from study outcome assessment. Upper trapezius endurance exercise will be performed through overhead shrugging with an elastic band while maintaining the neutral head and neck in sitting. Three set of 15 repeitations with 1-min rest between sets, at the exercise level standardised to a perceived exertion of 7/10 on the Borg Category Ratio 10 scale.

Deep cervical flexor motor control exercise (serves as the single exercise comparator to the experimental group i.e., hybrid group)

Deep cervical flexor motor-control will be performed by participants who are allocated to this exercise group. The same low-load craniocervical flexion exercise (for facilitation of the activation of longus capitis and longus colli) will be performed in supine crook lying position with the participants' head and neck in a neutral position. Training commences at the participant's baseline craniocervical flexion test endurance score (20mmHg to 30mmHg) for 10 repetiation of 10-second hold time using the pressure biofeedback unit, under the supervision by a physiotherapist, who is independent from study outcome assessment.

Upper trapezius endurance exercise (serves as the single exercise comparator to the experimental group i.e., hybrid group)

Upper trapezius endurance exercise (the same exercise component described in hybrid exercise programme) will be performed through overhead shrugging with an elastic band while maintaining the neutral head and neck in sitting. Three set of 15 repeitations with 1-min rest between sets, at the exercise level standardised to a perceived exertion of 7/10 on the Borg Category Ratio 10 scale.

Pain intensity of the neck region measured by the Numeric Pain Raing Scale 0-10

Functional disabilty related to chronic nonspecific neck pain will be measured by 1. Neck Disabilty Index (NDI) and 2. Disability of Arm, Shoulder and Hand Qestionnaire (DASH)

Short-Form 12 is used to assess the self-reported general health status of the participants.

Self-reported 1. Pain Self-Efficacy (measured by the Pain Self-Efficacy Questionnaire) (Lim et al., 2007) and 2. Exercise Self-Efficacy (measured by the Self-Efficacy for Exercise Scale (Wong et al., 2018).

Measures of pain senstivity assessed by pressure pain threshold and pincprick-induced temporal summation of pain, over the cervical extensors and upper trapezius muscles. Pressure pain threshold indexes pressure pain sensitivity, whereas temporal summation of pain quantifies the facilitation of pain responses to repeated noxious stimulation.

EIH is assessed immediately before and after the assigned exercise intervention within the same assessment session using the NPRS and PPT procedures described above. The magnitude of EIH is quantified using an EIH index based on the pre-to-post change in NPRS and PPT, calculated as pre-exercise NPRS - post-exercise NPRS and post-exercise PPT - pre-exercise PPT, respectively. Positive values indicate a hypoalgesic response (van Leer et al., 2017). Relative changes are additionally calculated as the corresponding change divided by the pre-exercise value × 100%.

Mechanical properties of the cervical extensors and upper trapeizus will be assessed using the myotonPRO device (for muscle tone, stiffness and elasticity) and the shearwave elastography (for stiffness).

Endurance index of upper trapezius will be assessed using a 5-min electrically evoked muscle-fatigue protocol based on the method described by Liss et al. (2020). Two surface electrodes are positioned over the upper trapezius , with a tri-axial accelerometer (Xsens DOT; Xsens Technologies B.V., Enschede, Netherlands) secured between the electrodes using double-sided tape and reinforced with micropore tape. Electrical stimulation is delivered using a 200-μs/50-μs pulse interval, with intensity individually adjusted between 15 and 25 mA to elicit vigorous but tolerable involuntary UT contractions. Acceleration is recorded simultaneously along three orthogonal axes (x, y, and z), and resultant acceleration is calculated using the formula reported. The endurance index is expressed as the percentage ratio of evoked twitch amplitude at the end of the 5-min stimulation period to that at baseline:

Vascularity (measured in terms of peak systolic velocity, end diastolic velocity, and resistance index) of cervical extensors (expressed in the deep cervical artery) and upper trapezius (expresssed in the trasverse cervical artery) and will be assessed using doppler ultrasonography (Adigozali et al., 2017).

Deep cervcal flexor activation and endurance will be assessed using the craniocervical flexion test (Jull et al., 2004 and 2019).

Joint position error of the neck and shoulder blade (scapula) will be assessed using the published testing protocols (AlDahas et al., 2025, de Vries et al., 2015, Scibek and Carcia, 2012, Kim et al., 2024).