Contralateral Resistance Training During Immobilization in Patients With Acromioclavicular Joint Injury

Effects of Contralateral Eccentric and Concentric Resistance Training During Immobilization on Neuromuscular Function, Functional Recovery, and Quality of Life in Patients With Acromioclavicular Joint Injury: A Randomized Controlled Trial

This randomized controlled trial aims to compare the effects of contralateral eccentric and concentric resistance training performed during the immobilization period following acromioclavicular joint injury. Immobilization is commonly prescribed after injury but may lead to reductions in muscle mass, neuromuscular function, force production, and upper-limb functionality.

Contralateral resistance training, also known as cross-education training, involves exercising the non-injured limb to induce beneficial adaptations in the immobilized limb through neural mechanisms. While both eccentric and concentric exercise may produce contralateral effects, their relative effectiveness in a clinical population remains unclear.

Participants with acute acromioclavicular joint injury requiring sling immobilization will be randomly assigned to either a contralateral eccentric training group or a contralateral concentric training group. During immobilization, participants will perform supervised resistance training with the non-injured upper limb. Following immobilization, all participants will receive the same standardized rehabilitation program.

Neuromuscular function, muscle morphology, force production, upper-limb function, and quality of life will be assessed before immobilization, after immobilization, and following rehabilitation. The findings may contribute to the development of more effective rehabilitation strategies for patients recovering from upper-limb injuries requiring temporary immobilization.

Acromioclavicular joint injury is one of the most common shoulder injuries in physically active individuals. Temporary immobilization using a sling is frequently prescribed during the acute phase of recovery; however, immobilization can result in rapid declines in muscle strength, muscle mass, neuromuscular function, and upper-limb performance.

Cross-education is a neurophysiological phenomenon whereby unilateral resistance training induces adaptations in the contralateral untrained limb. Previous experimental studies have demonstrated that resistance exercise performed with the non-immobilized limb may attenuate strength loss and neuromuscular impairments in an immobilized limb. However, the relative effectiveness of different muscle contraction modes during cross-education training in clinical populations remains poorly understood.

The purpose of this randomized controlled trial is to compare the effectiveness of contralateral eccentric versus contralateral concentric resistance training performed during the immobilization period in patients with acromioclavicular joint injury. Participants will be randomly allocated to one of two intervention groups: (1) contralateral eccentric resistance training or (2) contralateral concentric resistance training. Both interventions will be performed using the non-injured upper limb during the period of prescribed sling immobilization.

Participants will undergo comprehensive assessments before immobilization, immediately after immobilization, and after completion of a standardized rehabilitation program. Outcomes will include measures of neuromuscular function obtained through peripheral nerve stimulation, transcranial magnetic stimulation, electromyography, and voluntary force assessments. Muscle morphology will be evaluated using ultrasound imaging, while upper-limb function and quality of life will be assessed using validated clinical questionnaires.

Following immobilization, all participants will receive the same rehabilitation program focused on restoring shoulder stability, muscle strength, and functional capacity. The primary objective is to determine whether eccentric or concentric contralateral resistance training more effectively preserves neuromuscular function and facilitates recovery following immobilization.

The results of this study may provide evidence to optimize rehabilitation strategies for patients with acromioclavicular joint injuries and other musculoskeletal conditions requiring temporary upper-limb immobilization.

Inclusion Criteria:

• Men and women aged 18 to 36 years.
• Diagnosis of acute acromioclavicular joint injury confirmed by an orthopedic surgeon.
• Physician-prescribed upper-limb immobilization using a sling for approximately 2 to 4 weeks, with or without surgical repair.
• Ability to understand study procedures and provide written informed consent.
• Medical clearance to participate in the rehabilitation and resistance training program.

Exclusion Criteria:

• Previous surgery or severe musculoskeletal injury affecting either upper limb within the previous 12 months.
• Neurological disorders affecting motor function or neuromuscular performance.
• Contraindications to transcranial magnetic stimulation according to established safety guidelines.
• Current participation in another clinical trial or structured upper-limb rehabilitation program.
• Cognitive impairment or inability to comply with study procedures.
• Pregnancy.
• Any medical condition that, in the opinion of the investigators, may compromise participant safety or study participation.