The Effects of Exercise Training on Shoulder Neuromuscular Control
| Status: | Recruiting |
|---|---|
| Healthy: | No |
| Age Range: | 18 - 50 |
| Updated: | 7/11/2015 |
| Start Date: | May 2014 |
| Contact: | Andrew Karduna |
| Email: | Karduna@uoregon.edu |
| Phone: | 1-541-346-0438 |
Dynamic control of the rotator cuff muscles plays an important role in stabilizing the
shoulder during motion. Impairment in the neuromuscular control of these muscles may to lead
to injury and pain. Rehabilitation programs have moderate success in decreasing pain and
improving shoulder function. While most of these programs target the rotator cuff, it is
still unknown if they serve to improve the neuromuscular control of the rotator cuff
muscles. The rehabilitation may induce neurological and physiologic changes in neuromuscular
structures and thus alter the neuromuscular control of the entire shoulder complex.
Kinematics and electromyographic (EMG) activities have been widely used to study
neuromuscular control. However, corticospinal excitability, which has been widely examined
in the patients with neurological disorders, provides a more detailed account of central
control from the primary motor cortex through the spinal cord to the muscles. This
assessment of neuromuscular control will serve to illuminate the ability of the shoulder
muscles to handle the stress from activities such as overhead sports activities and carrying
or lifting heavy objects. This approach could be used to help design efficient training
program for athletes and effective rehabilitation program for patients with shoulder
injuries. The purpose of the proposed study is to investigate the effect of exercise
treatment effect on the proprioception, kinematics, EMG and corticospinal excitability of
shoulder muscles, including the deltoid and rotator cuff muscles.
shoulder during motion. Impairment in the neuromuscular control of these muscles may to lead
to injury and pain. Rehabilitation programs have moderate success in decreasing pain and
improving shoulder function. While most of these programs target the rotator cuff, it is
still unknown if they serve to improve the neuromuscular control of the rotator cuff
muscles. The rehabilitation may induce neurological and physiologic changes in neuromuscular
structures and thus alter the neuromuscular control of the entire shoulder complex.
Kinematics and electromyographic (EMG) activities have been widely used to study
neuromuscular control. However, corticospinal excitability, which has been widely examined
in the patients with neurological disorders, provides a more detailed account of central
control from the primary motor cortex through the spinal cord to the muscles. This
assessment of neuromuscular control will serve to illuminate the ability of the shoulder
muscles to handle the stress from activities such as overhead sports activities and carrying
or lifting heavy objects. This approach could be used to help design efficient training
program for athletes and effective rehabilitation program for patients with shoulder
injuries. The purpose of the proposed study is to investigate the effect of exercise
treatment effect on the proprioception, kinematics, EMG and corticospinal excitability of
shoulder muscles, including the deltoid and rotator cuff muscles.
Significance
The human shoulder complex sacrifices stability in exchange for a large range of motion
necessary for hand manipulation. Due to the inherent instability of the bony congruence and
ligament constraint, dynamic control of the muscles plays an important role in stabilizing
the shoulder during motion. The rotator cuff muscles serve as the chief stabilizer of the
shoulder joint, while the deltoid provides most of the torque necessary for motion.
Therefore, the coordination of the deltoid and the rotator cuff muscles is essential for
smooth and efficient shoulder function. Impairment in the neuromuscular control of these
muscles may to lead to injury and pain. Consequently, rehabilitation programs aim to restore
the normal neuromuscular control of these shoulder muscles in order to help decrease pain
and improve shoulder function. Although rehabilitation programs have demonstrated positive
effects on pain decrease and functional improvement, it is still unknown if they serve to
improve the neuromuscular control of the shoulder muscles.
While the deltoid provides most of the torque necessary to elevation the shoulder, it can
also produce a superiorly directly force on the glenoid. This shear force tends to pull the
humeral head superiorly, which can result in a decrease in the subacromial space. When the
rotator cuff muscles function properly, the line of action of the rotator cuff muscles
result in a centering force, which can help maintain the humeral head in the center of the
glenoid fossa. However, it has been hypothesized that if the rotator cuff muscles are not
able to produce sufficient force during arm movement, the superior shear force produced by
the deltoid results in humeral head superior translation. This abnormal displacement can
result in impingement of subacromial tissues and ultimately leading to tissue injury and
pain.
Traditionally, shoulder rehabilitation programs focus on strengthening the rotator cuff
muscles by using shoulder movement in which the rotator cuff muscles show high muscle
activity. However, although these activities lead to a strengthening of the rotator cuff,
what is unknown is whether the repetitive stress imposed on the rotator cuff results in
neuromuscular adaptations that will help counteract the deltoid shear force.
This stress of rehabilitation may induce the neurological and physiologic changes in
neuromuscular structures and thus alters the neuromuscular control of the entire shoulder
complex. Kinematics and electromyographic (EMG) measurements have been widely used to study
neuromuscular control. While kinematic measures show movement patterns, EMG demonstrates the
timing, sequence, and magnitude of the muscle firing. Abnormal kinematics and EMG patterns
have been demonstrated in patients with shoulder impingement. Measuring parameters of
neuromuscular control can lead to a better understanding of the underlying mechanism of
shoulder exercise training and how the neuromuscular structures adapt to the stress of the
exercise training. More specifically, these assessments can be used to assess whether a
rehabilitation program results in a positive adaptation that can help the shoulder muscles
handle the stress from activities such as overhead sports activities and carrying or lifting
heavy objects. Ultimately, this could be used to design more efficient training program for
athletes and effective rehabilitation program for patients with shoulder injuries.
Innovation
When shoulder neuromuscular control is investigated in the fields of biomechanics,
orthopaedic rehabilitation, and sports, the focus is generally on kinematics and EMG. These
kinematics and EMG parameters represent how the shoulder complex is controlled during
movement as the result of motor command execution. Corticospinal excitability, which has
been widely examined in patients with neurological disorders, has also been recently applied
in biomechanics, orthopaedic rehabilitation, and sports fields. Corticospinal excitability
represents the efficacy of neural transmission along the corticospinal pathway. In addition
to neurological impairment, orthopaedic injury and pain can also affect corticospinal
excitability. For example, in subjects with non-traumatic shoulder instability, the lower
trapezius demonstrates decreased excitability. Also, experimental tonic muscle pain over the
first dorsal interosseous results in inhibition of cortical and spinal excitability.
Similarly, experimentally-induced acute low lumbar pain is associated with different effects
on trunk muscles. The deep abdominal muscles, such as the transversus abdominis, showed
reduced corticospinal excitability. In contract, more superficial muscles, such as the
lumbar erector spinae and external oblique abdominis, demonstrated increased excitability.
In addition to kinematics and EMG measurements, which demonstrate the overall motor
strategy, the corticospinal excitability is another promising parameter to investigate the
details about how the deltoid and rotator cuff muscles are controlled from the primary motor
cortex through the spinal cord to the muscle.
While consistent evidence suggests that motor skill training is associated with increased
excitability, the effects of strength training on corticospinal excitability are still not
well known and may depend on the muscles and training task. The training of neuromuscular
control may be associated with both motor learning and strength training. The control and
firing pattern may be directly re-learned consciously, which involves increases in strength
and motor learning. Since it is associated with a learning process, excitability may
increase after training. It has been shown that changes in the excitability are correlated
with a motor learning effect, so that changes in excitability after training may be
correlated with changes of rotator cuff EMG. After repetitive practice, the conscious
movement patterns may become automatic thus changing the EMG pattern of rotator cuff
activation.
The purposes of the study are to (1) investigate the effect of exercise training on the
neuromuscular control of shoulder complex in healthy subjects, including kinematics, EMG and
corticospinal excitability, and (2) to examine the relationship between the corticospinal
excitability, EMG and force measures. The results of the study may help to understand the
underlying neurological and biomechanic mechanism of exercise training and help to design
the training or rehabilitation protocols for the athletes or the patient with shoulder
injuries.
Approach
A randomized controlled experimental design will be used to investigate the effect of
rotator cuff exercise. Healthy subjects will be recruited and randomly assigned to two
groups, exercise and control groups.
All measures will be made twice, before and after a four-week treatment. Fine-wire
electromyography (EMG) electrodes will be inserted into the supraspinatus and infraspinatus
muscles of the rotator cuff. Surface EMG electrodes will be used for the middle deltoid and
scapular muscles. Transcranial magnetic stimulation (TMS) will be used to assess the
corticospinal excitability of the deltoid and rotator cuff muscles. A flat double-coil
stimulation coil will be used to provide a single-pulse stimulus over the motor cortex,
approximately 4 cm lateral of the bisection of the mid line and the biauricular line.
Electromagnetic tracking sensors will be attached to the arm, scapula and thorax to measure
shoulder kinematics.
The parameters of corticospinal excitability will also measured when the arm is at 90° of
elevation with a baseline muscle contraction level of 10% maximum voluntary contraction
(MVC). TMS stimulation intensity will be set at 10% below threshold and increased in 5%
increments until the response saturates. Five stimuli will be delivered at each intensity of
stimulation. The peak-to-peak amplitude of the motor evoked potential (MEP) will be measured
and averaged across the five trials at each intensity. The curve of the relationship between
stimulation intensity and the MEP amplitude is sigmoidal and will be fit with the Boltzmann
equation.
MEP(s) = MEPmax/(1+ e^(m(S - 50s)))
In this equation, MEP(s) is the amplitude of motor evoked potential, MEPmax is the maximum
MEP amplitude, m is the slope of the function, and S50 is the stimulus intensity at which
the MEP is 50% of MEPmax. The peak slope of the function occurs at S50. The threshold of the
curve is the x-intercept of the tangent to the function at the point of maximal slope.
Three parameters, MEPmax, m, and x-intercept threshold, will be used to model the
corticospinal excitability, which provides a more details of the excitability of the
corticospinal tract. The value of x-intercept threshold is similar to the motor threshold
and represents the stimulus intensity needed to activate the most excitable corticospinal
elements and motoneurons. The slope indicates the recruitment efficiency (gain) of the
corticospinal tract. The MEPmax reflects the balance between excitatory and inhibitory
components of the corticospinal tract.
Scapular and humeral kinematics and the dynamic EMG of rotator cuff and deltoid muscles will
be recorded during three trials of arm elevation at scapular plane. The root mean square EMG
data will be calculated over four 30° increments of motion during arm elevation from 0° to
120°. Scapular kinematics will be presented at 30°, 60°, 90° and 120° of humeral elevation.
The subjects will be tested the shoulder proprioception. They will wear a goggle, which will
give the visual cues to guide them to reach the target. Three target positions will be
presented: humerothoracic elevation angles of 50°, 70°, and 90° in the scapular plane. The
subjects will be instructed to reach the target again without any visual cues after relaxing
their arms at the side. The errors between the target angle and the angle they returned will
be calculated.
Both treatment programs will last four weeks. The subjects in the exercise group will have
standard rehabilitation exercise for the shoulder impingement syndrome. The exercise will be
based on a previous treatment study conducted by Dr. Karduna and will be modified to
emphasize on facilitation and strengthening the rotator cuff muscles. The subjects in the
control group will receive no exercise. The control subjects will be asked to maintain their
regular activities and only have two assessments.
A two-way mixed-design analysis of variance (ANOVA) will be used to examine the differences
in neuromuscular control following the treatment between the control and exercise groups.
The dependent variables will be the changes of kinematics, EMG and excitability following
the treatment. The independent variables will be humeral elevation angles and groups. The
correlation between changes of TMS measures, the EMG measures, and the forces will be
examined by with a correlation analysis.
The human shoulder complex sacrifices stability in exchange for a large range of motion
necessary for hand manipulation. Due to the inherent instability of the bony congruence and
ligament constraint, dynamic control of the muscles plays an important role in stabilizing
the shoulder during motion. The rotator cuff muscles serve as the chief stabilizer of the
shoulder joint, while the deltoid provides most of the torque necessary for motion.
Therefore, the coordination of the deltoid and the rotator cuff muscles is essential for
smooth and efficient shoulder function. Impairment in the neuromuscular control of these
muscles may to lead to injury and pain. Consequently, rehabilitation programs aim to restore
the normal neuromuscular control of these shoulder muscles in order to help decrease pain
and improve shoulder function. Although rehabilitation programs have demonstrated positive
effects on pain decrease and functional improvement, it is still unknown if they serve to
improve the neuromuscular control of the shoulder muscles.
While the deltoid provides most of the torque necessary to elevation the shoulder, it can
also produce a superiorly directly force on the glenoid. This shear force tends to pull the
humeral head superiorly, which can result in a decrease in the subacromial space. When the
rotator cuff muscles function properly, the line of action of the rotator cuff muscles
result in a centering force, which can help maintain the humeral head in the center of the
glenoid fossa. However, it has been hypothesized that if the rotator cuff muscles are not
able to produce sufficient force during arm movement, the superior shear force produced by
the deltoid results in humeral head superior translation. This abnormal displacement can
result in impingement of subacromial tissues and ultimately leading to tissue injury and
pain.
Traditionally, shoulder rehabilitation programs focus on strengthening the rotator cuff
muscles by using shoulder movement in which the rotator cuff muscles show high muscle
activity. However, although these activities lead to a strengthening of the rotator cuff,
what is unknown is whether the repetitive stress imposed on the rotator cuff results in
neuromuscular adaptations that will help counteract the deltoid shear force.
This stress of rehabilitation may induce the neurological and physiologic changes in
neuromuscular structures and thus alters the neuromuscular control of the entire shoulder
complex. Kinematics and electromyographic (EMG) measurements have been widely used to study
neuromuscular control. While kinematic measures show movement patterns, EMG demonstrates the
timing, sequence, and magnitude of the muscle firing. Abnormal kinematics and EMG patterns
have been demonstrated in patients with shoulder impingement. Measuring parameters of
neuromuscular control can lead to a better understanding of the underlying mechanism of
shoulder exercise training and how the neuromuscular structures adapt to the stress of the
exercise training. More specifically, these assessments can be used to assess whether a
rehabilitation program results in a positive adaptation that can help the shoulder muscles
handle the stress from activities such as overhead sports activities and carrying or lifting
heavy objects. Ultimately, this could be used to design more efficient training program for
athletes and effective rehabilitation program for patients with shoulder injuries.
Innovation
When shoulder neuromuscular control is investigated in the fields of biomechanics,
orthopaedic rehabilitation, and sports, the focus is generally on kinematics and EMG. These
kinematics and EMG parameters represent how the shoulder complex is controlled during
movement as the result of motor command execution. Corticospinal excitability, which has
been widely examined in patients with neurological disorders, has also been recently applied
in biomechanics, orthopaedic rehabilitation, and sports fields. Corticospinal excitability
represents the efficacy of neural transmission along the corticospinal pathway. In addition
to neurological impairment, orthopaedic injury and pain can also affect corticospinal
excitability. For example, in subjects with non-traumatic shoulder instability, the lower
trapezius demonstrates decreased excitability. Also, experimental tonic muscle pain over the
first dorsal interosseous results in inhibition of cortical and spinal excitability.
Similarly, experimentally-induced acute low lumbar pain is associated with different effects
on trunk muscles. The deep abdominal muscles, such as the transversus abdominis, showed
reduced corticospinal excitability. In contract, more superficial muscles, such as the
lumbar erector spinae and external oblique abdominis, demonstrated increased excitability.
In addition to kinematics and EMG measurements, which demonstrate the overall motor
strategy, the corticospinal excitability is another promising parameter to investigate the
details about how the deltoid and rotator cuff muscles are controlled from the primary motor
cortex through the spinal cord to the muscle.
While consistent evidence suggests that motor skill training is associated with increased
excitability, the effects of strength training on corticospinal excitability are still not
well known and may depend on the muscles and training task. The training of neuromuscular
control may be associated with both motor learning and strength training. The control and
firing pattern may be directly re-learned consciously, which involves increases in strength
and motor learning. Since it is associated with a learning process, excitability may
increase after training. It has been shown that changes in the excitability are correlated
with a motor learning effect, so that changes in excitability after training may be
correlated with changes of rotator cuff EMG. After repetitive practice, the conscious
movement patterns may become automatic thus changing the EMG pattern of rotator cuff
activation.
The purposes of the study are to (1) investigate the effect of exercise training on the
neuromuscular control of shoulder complex in healthy subjects, including kinematics, EMG and
corticospinal excitability, and (2) to examine the relationship between the corticospinal
excitability, EMG and force measures. The results of the study may help to understand the
underlying neurological and biomechanic mechanism of exercise training and help to design
the training or rehabilitation protocols for the athletes or the patient with shoulder
injuries.
Approach
A randomized controlled experimental design will be used to investigate the effect of
rotator cuff exercise. Healthy subjects will be recruited and randomly assigned to two
groups, exercise and control groups.
All measures will be made twice, before and after a four-week treatment. Fine-wire
electromyography (EMG) electrodes will be inserted into the supraspinatus and infraspinatus
muscles of the rotator cuff. Surface EMG electrodes will be used for the middle deltoid and
scapular muscles. Transcranial magnetic stimulation (TMS) will be used to assess the
corticospinal excitability of the deltoid and rotator cuff muscles. A flat double-coil
stimulation coil will be used to provide a single-pulse stimulus over the motor cortex,
approximately 4 cm lateral of the bisection of the mid line and the biauricular line.
Electromagnetic tracking sensors will be attached to the arm, scapula and thorax to measure
shoulder kinematics.
The parameters of corticospinal excitability will also measured when the arm is at 90° of
elevation with a baseline muscle contraction level of 10% maximum voluntary contraction
(MVC). TMS stimulation intensity will be set at 10% below threshold and increased in 5%
increments until the response saturates. Five stimuli will be delivered at each intensity of
stimulation. The peak-to-peak amplitude of the motor evoked potential (MEP) will be measured
and averaged across the five trials at each intensity. The curve of the relationship between
stimulation intensity and the MEP amplitude is sigmoidal and will be fit with the Boltzmann
equation.
MEP(s) = MEPmax/(1+ e^(m(S - 50s)))
In this equation, MEP(s) is the amplitude of motor evoked potential, MEPmax is the maximum
MEP amplitude, m is the slope of the function, and S50 is the stimulus intensity at which
the MEP is 50% of MEPmax. The peak slope of the function occurs at S50. The threshold of the
curve is the x-intercept of the tangent to the function at the point of maximal slope.
Three parameters, MEPmax, m, and x-intercept threshold, will be used to model the
corticospinal excitability, which provides a more details of the excitability of the
corticospinal tract. The value of x-intercept threshold is similar to the motor threshold
and represents the stimulus intensity needed to activate the most excitable corticospinal
elements and motoneurons. The slope indicates the recruitment efficiency (gain) of the
corticospinal tract. The MEPmax reflects the balance between excitatory and inhibitory
components of the corticospinal tract.
Scapular and humeral kinematics and the dynamic EMG of rotator cuff and deltoid muscles will
be recorded during three trials of arm elevation at scapular plane. The root mean square EMG
data will be calculated over four 30° increments of motion during arm elevation from 0° to
120°. Scapular kinematics will be presented at 30°, 60°, 90° and 120° of humeral elevation.
The subjects will be tested the shoulder proprioception. They will wear a goggle, which will
give the visual cues to guide them to reach the target. Three target positions will be
presented: humerothoracic elevation angles of 50°, 70°, and 90° in the scapular plane. The
subjects will be instructed to reach the target again without any visual cues after relaxing
their arms at the side. The errors between the target angle and the angle they returned will
be calculated.
Both treatment programs will last four weeks. The subjects in the exercise group will have
standard rehabilitation exercise for the shoulder impingement syndrome. The exercise will be
based on a previous treatment study conducted by Dr. Karduna and will be modified to
emphasize on facilitation and strengthening the rotator cuff muscles. The subjects in the
control group will receive no exercise. The control subjects will be asked to maintain their
regular activities and only have two assessments.
A two-way mixed-design analysis of variance (ANOVA) will be used to examine the differences
in neuromuscular control following the treatment between the control and exercise groups.
The dependent variables will be the changes of kinematics, EMG and excitability following
the treatment. The independent variables will be humeral elevation angles and groups. The
correlation between changes of TMS measures, the EMG measures, and the forces will be
examined by with a correlation analysis.
Inclusion Criteria:
- Healthy subjects
Exclusion Criteria:
- Less than 135 degrees of active humeral elevation in the scapular plane
- Prior shoulder and cervical surgery
- Presence of shoulder and neck pain
- Had history of head, cervical or shoulder pain or pathology
- Stroke and neurological impairment
- History of seizures
- Taking anti-seizure and anti-depressive medication
- With pacemaker and other magnetic implant
- Pregnancy
- Athletes performing upper extremity exercise
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