This randomized controlled clinical trial aims to evaluate the effectiveness of a standardized shoulder stabilization exercise program in amateur volleyball players diagnosed with atraumatic shoulder instability. Shoulder pain is one of the most prevalent musculoskeletal complaints, affecting up to two-thirds of the general population at some point in life and frequently leading to long-term symptoms, functional limitations, sleep disturbances, and high socio-economic costs. Atraumatic glenohumeral instability is particularly common among athletes performing overhead movements, such as volleyball players, who are repeatedly exposed to high-velocity external and internal rotation actions during serves and spikes.
The Derby Shoulder Instability Rehabilitation Programme (DSIRP) is a structured, reproducible protocol integrating strengthening, proprioceptive, neuromuscular control, plyometric, and speed-oriented exercises. Although widely used in clinical practice, evidence supporting its superiority over the natural progression of the condition remains limited. More than 80% of physiotherapists in the United Kingdom do not use specific standardized protocols for atraumatic shoulder instability, highlighting the need for high-quality clinical trials that evaluate structured rehabilitation approaches.
This study will recruit amateur volleyball players aged 20 to 30 years with a clinical diagnosis of atraumatic shoulder instability lasting more than 3 months. Participants will be randomized (1:1) into two parallel groups: an experimental group performing the DSIRP for 8 weeks (three 25-minute sessions per week), and a control group following a "wait-and-see" approach. Outcome measures will be assessed at baseline, 1 month, and 2 months (post-intervention). The primary outcomes include pain intensity measured with the Numeric Pain Rating Scale and shoulder disability measured with the Spanish version of the Shoulder Pain and Disability Index. Secondary outcomes include external rotation strength, grip strength, shoulder range of motion, and health-related quality of life assessed with the SF-12 questionnaire. All measurements use validated instruments with high reliability for clinical and research settings.
Statistical analysis will follow an intention-to-treat approach using mixed-model repeated-measures ANOVA or non-parametric alternatives when appropriate. Effect sizes and Bonferroni correction for multiple comparisons will be applied. An independent biostatistician blinded to allocation will conduct the analysis. The study follows CONSORT and TIDieR guidelines for reporting and intervention description.
This trial seeks to determine whether a structured, progressive stabilization protocol offers clinically meaningful improvements in pain, disability, strength, mobility, and quality of life compared with no intervention in young volleyball players with atraumatic shoulder instability. Results may support the implementation of standardized rehabilitation strategies in physiotherapy practice for this condition.
Amateur volleyball players.
Age range: 18 to 30 years.
Clinical diagnosis of atraumatic shoulder instability.
Symptom duration greater than 3 months.
Previous surgeries on the affected shoulder.
Previous fractures of the affected shoulder.
History of traumatic shoulder dislocation.
Shoulder pain originating from cervical spine pathology.
Parallel
Exercise
Other interventionParticipants assigned to the intervention group will complete the Derby Shoulder Instability Rehabilitation Programme (DSIRP), a structured and progressive exercise-based protocol specifically designed for individuals with atraumatic shoulder instability. The program integrates strengthening exercises, proprioceptive and neuromuscular control training, plyometric drills, and speed-oriented stabilization tasks. Progression through the exercises is criterion-based, following predefined functional milestones to ensure appropriate challenge and individualized adaptation. The DSIRP focuses on enhancing dynamic glenohumeral stability through rotator-cuff activation, scapular control, and kinetic-chain coordination. Each session includes components targeting isometric and isotonic strengthening, closed-chain stability tasks, rhythmic stabilization, rapid-response perturbation activities, and overhead-sport-specific movement patterns relevant to volleyball athletes.
Pain intensity
Pain intensity will be assessed using the Numeric Pain Rating Scale (NPRS), an 11-point numerical rating scale ranging from 0 ("no pain") to 10 ("worst imaginable pain"). The NPRS has demonstrated adequate test-retest reliability, with intraclass correlation coefficients (ICC) ranging from 0.63 to 0.92, and strong internal consistency, with Cronbach's alpha values between 0.84 and 0.98, as previously reported in studies evaluating its psychometric properties (Stratford \& Spadoni, 2001; Jensen \& McFarland, 1993; Jensen et al., 1986)
Shoulder disability
Shoulder disability will be assessed using the Spanish version of the Shoulder Pain and Disability Index (SPADI), a self-reported questionnaire designed to measure shoulder pain and functional limitations through 13 items originally developed by Williams et al. (1995). The instrument has demonstrated the ability to discriminate between patients who improve and those who worsen (Roy et al., 2009), and its Spanish cross-cultural adaptation preserves the original structure and psychometric properties, providing a reliable and valid patient-reported outcome measure suitable for both clinical practice and research (Membrilla-Mesa et al., 2015)
External rotation strength
Isometric external rotation strength of the shoulder will be measured using the MicroFET 2 MT Digital Handheld Dynamometer (Hoggan Health Industries, West Draper, UT). Handheld dynamometry has shown good to excellent intra-examiner reliability for isometric shoulder strength assessment, with intraclass correlation coefficients ranging from 0.87 to 0.99, according to prior studies evaluating its reproducibility in clinical and research settings (McLaine et al., 2016; Holt et al., 2016)
Hand grip strength
Hand grip strength will be measured using a Jamar handheld dynamometer (Sammons Preston Rolyan, Bolingbrook, IL), a device widely recognized for its robustness and reproducibility. This instrument has demonstrated good to excellent intra-examiner reliability for isometric grip strength outcomes, with intraclass correlation coefficients ranging from 0.85 to 0.98 in previous validation studies (Roberts et al., 2011)
Shoulder mobility
Shoulder range of motion will be assessed for flexion, abduction, external rotation at 0°, external rotation at 90°, and internal rotation at 90° of abduction using a validated smartphone inclinometer application (Plaincode Software Solutions, Gunzenhausen, Germany). This tool has shown excellent inter-examiner reliability and validity in symptomatic individuals, with intraclass correlation coefficients greater than 0.80 for shoulder mobility measurements (Werner et al., 2014)
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