Contralateral Resistance Training During Immobilization in Patients With Acromioclavicular Joint Injury (CROSS-ACD)

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.

Study Overview

• Status: Recruiting
• Conditions: Acromioclavicular Joint Dislocation; Acromioclavicular Joint Injury
• Intervention / Treatment: Behavioral: Contralateral Eccentric Resistance Training; Behavioral: Contralateral Concentric Resistance Training

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Estimated): 16
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Omar E Valdés Tapia, PT, MSc, PhD(c); Phone Number: +569 74082822; Email: o.valdestapia@uandresbello.edu

Study Locations

• Chile
  • Providencia
    • Santiago, Providencia, Chile
      • Recruiting
      • Clínica Indisa
      • Contact: Claudio Chamorro Lange, PhD; Phone Number: +569 94398014; Email: claudio.chamorro@unab.cl

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

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.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Contralateral Eccentric Training; Participants will perform supervised contralateral eccentric resistance training with the non-injured upper limb during the period of physician-prescribed sling immobilization following acute acromioclavicular joint injury, with or without surgical repair. The immobilization period is expected to last approximately 2 to 4 weeks depending on clinical management. Following immobilization, participants will complete a standardized 4-week rehabilitation program.	Behavioral: Contralateral Eccentric Resistance Training; Supervised unilateral eccentric elbow flexor training performed with the non-injured limb during sling immobilization (2-4 weeks). Training is performed 3 times/week, 5 sets of 8-12 repetitions at 60-90% 1RM, with 4-second contractions and 3-minute rest intervals between sets.
Active Comparator: Contralateral Concentric Training; Participants will perform supervised contralateral concentric resistance training with the non-injured upper limb during the period of physician-prescribed sling immobilization following acute acromioclavicular joint injury, with or without surgical repair. The immobilization period is expected to last approximately 2 to 4 weeks depending on clinical management. Following immobilization, participants will complete the same standardized 4-week rehabilitation program.	Behavioral: Contralateral Concentric Resistance Training; Supervised unilateral concentric elbow flexor training performed with the non-injured limb during sling immobilization (2-4 weeks). Training is performed 3 times/week, 5 sets of 8-12 repetitions at 60-90% 1RM, with 4-second contractions and 3-minute rest intervals between sets.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Maximal Voluntary Isometric Contraction	Maximal voluntary isometric force of the injured upper limb assessed using a calibrated dynamometer. Force values will be recorded during standardized maximal isometric contractions and used to evaluate changes in muscle performance throughout immobilization and rehabilitation.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Rate of Force Development	Rate of force development (RFD) of the injured upper limb assessed during maximal voluntary isometric contractions using a calibrated dynamometer. RFD will be calculated from the force-time curve and used as an indicator of explosive force production and neuromuscular performance.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Elbow Flexors Voluntary Activation	Voluntary activation of the elbow flexors assessed using the interpolated twitch technique during maximal voluntary isometric contractions. Values will be expressed as a percentage of voluntary neural drive to the muscle.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii Motor Supramaximal Response Amplitude	Peak-to-peak amplitude of the motor supramaximal response (MSUP) evoked by peripheral nerve stimulation during submaximal contractions as an indicator of motor pathway excitability.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii Motor Evoked Potential Amplitude	Motor evoked potential (MEP) amplitude elicited by transcranial magnetic stimulation and normalized to peripheral responses to assess corticospinal excitability.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii Silent Period Duration	Duration of the electromyographic silent period following transcranial magnetic stimulation during voluntary contractions as an indicator of cortical inhibition.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii Short-Interval Intracortical Inhibition	Short-interval intracortical inhibition assessed using paired-pulse transcranial magnetic stimulation as an index of intracortical inhibitory function.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii Cervicomedullary Motor Evoked Potential Amplitude	Motor unit discharge characteristics assessed using high-density surface electromyography, including discharge rate, recruitment thresholds, and estimates of intrinsic motoneuron properties.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii Motor Unit Behavior	Motor unit discharge characteristics assessed using high-density surface electromyography, including discharge rate, recruitment thresholds, and estimates of intrinsic motoneuron properties.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii MMAX Amplitude	Peak-to-peak amplitude of the maximal compound muscle action potential (MMAX) evoked by peripheral nerve stimulation as an indicator of peripheral excitability.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii Peripheral Contractile Properties	Evoked twitch and doublet force responses obtained using peripheral nerve stimulation to assess muscle contractile function.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Biceps Brachii Muscle Thickness	Muscle thickness assessed by B-mode ultrasonography as an indicator of muscle morphology and preservation during immobilization and rehabilitation.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Upper Limb Function (QuickDASH)	Upper-limb disability and functional status assessed using the Quick Disabilities of the Arm, Shoulder and Hand (QuickDASH) questionnaire.	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
Health-Related Quality of Life (SF-36)	Health-related quality of life assessed using the 36-Item Short Form Health Survey (SF-36).	Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)

Collaborators and Investigators

• Sponsor: Universidad Nacional Andres Bello
• Investigators: Study Director: Claudio Chamorro Lange, PhD, Universidad Nacional Andres Bello; Study Director: Luis Peñailillo Escaráte, PhD, Universidad Nacional Andres Bello

Study record dates

Study Major Dates

• Study Start (Actual): January 1, 2026
• Primary Completion (Estimated): July 1, 2027
• Study Completion (Estimated): July 1, 2027

Study Registration Dates

• First Submitted: May 29, 2026
• First Submitted That Met QC Criteria: May 29, 2026
• First Posted (Actual): June 5, 2026

Study Record Updates

• Last Update Posted (Actual): June 5, 2026
• Last Update Submitted That Met QC Criteria: May 29, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Rehabilitation; Physical Therapy; Electromyography; Transcranial Magnetic Stimulation; Muscle Strength; Resistance Training; Immobilization; Shoulder Rehabilitation; Neuromuscular Function; Eccentric Exercise; Concentric Exercise; Cross-Education; Upper Limb Function; Contralateral Training; Acromioclavicular Joint Injury
• Other Study ID Numbers: DI-03-CBC/22; 21261279 (Other Grant/Funding Number: ANID/Beca de Doctorado Nacional 2026, Chile.); DI-07-25/INI (Other Grant/Funding Number: Concurso de Iniciación a la Investigación UNAB 2025, Chile.); 24 010884 01 (Other Grant/Funding Number: Programme Ambition International 2024, La Région Auvergne Rhône Alpes (France)".)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED
• IPD Plan Description: The investigators have not yet determined whether individual participant data will be shared. A final data sharing plan will be established following study completion and publication of the primary results.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No