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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
SINGLE
Enrollment
16
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.
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.
Clínica Indisa
Santiago, Providencia, Chile
RECRUITINGMaximal 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. Unit: Newtons (N)
Time frame: 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. Unit: N·s-¹ (N/s)
Time frame: Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
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. Unit: %
Time frame: 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. Unit: mV
Time frame: 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. Unit: mV
Time frame: 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. Unit: ms
Time frame: 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. Unit: mV
Time frame: 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. Unit: mV
Time frame: 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. Unit: pulses/s (pps)
Time frame: 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. Unit: mV
Time frame: 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. Unit: N
Time frame: 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. Unit: mm
Time frame: 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. Unit: 0-100 points
Time frame: 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). Unit: 0-100 points
Time frame: Baseline, post-immobilization (2-4 weeks), and post-rehabilitation (6-8 weeks)
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