3.2.4. Additional Electrodiagnostics Techniques

In addition to EMG, more specific electrodiagnostic techniques can be used in performers. These techniques include upper-limb H-reflex reciprocal inhibition [84], somatosensory evoked potential brain mapping techniques, and transcranial magnetic stimulation (TMS) [65,85], and these have been used particularly in studying focal dystonia and cortical excitability/plasticity. Repetitive TMS is being used for the treatment of complex regional pain syndrome (CRPS), a chronic progressive disease characterized by severe pain combined with sensory, autonomic, and motor disturbances [86].

3.2.5. EMG Applications in Performers

(a) Co-Activation of Muscles

(b) Muscle Imbalance and Asymmetry

(c) Risk Assessment (e.g., Increased Deltoid Activity)

With raising the arm the deltoid also raises the humeral head. To counterweight the subsequent compression of the humeral head against the undersurface of the acromion and reduce the risk of injury of the supraspinatus tendon, simultaneous contractions of the infraspinatus, teres minor and subscapularis rotator cuff muscles occur [87]. An increased deltoid muscle activity will usually evoke a decrease in subacromial space and an increased compression of the humeral head, thus augmenting the hazard of injuring the supraspinatus tendon.

(d) Subacromial Impingement Syndrome (SAIS)

Subacromial impingement syndrome (SAIS), the commonest disorder of the shoulder, is a painful disorder due to loss of subacromial space [88].

(e) Assessment of Shoulder Rest and Backrest Support

EMG of the upper arm muscles of the violin players can also be used to assess the efficacy of a shoulder rest attached to the violin. The EMG signals (rectified EMG) of the left trapezius and right sternocleidomastoid muscles reveal a significant reduction in muscle activity when the shoulder rest is used [62,91]. EMG reduction in these muscles (thus their forces) is associated with their increased lever-arm.

(f) Comparison Between Upper Strings and Cello Playing

Opposed asymmetry differences in the middle and lower trapezius MAI in the upper string and cello groups are also noted between bowing down (from tail to tip) and bowing up (from tip to tail). In upper strings, sliding the bow up requires higher muscle activity (about 50% higher than sliding it down) [56,59]. The reason is that there is a static loading of the left shoulder to support the instrument, and a dynamic, repetitive loading of the right shoulder to facilitate the bowing, the latter being eased by gravity during the bowing down movement [57,68].

(g) Piriformis Muscle Syndrome

A potential syndrome of great discomfort in cellists is piriformis syndrome, associated with the piriformis muscle, which can particularly become tight and cause pain through pinching of the sciatic nerve [43]. Although a monitoring of the surface EMG of the piriformis is possible [92], it might be preferable to make use of fine-wire electrodes, due to the deep location of the muscle [93].

(h) Muscle Fatigue

Through the processing of the EMG signal, information about muscle fatigue can be obtained both in the time domain (e.g., amplitude of the normalized the rectified signal) and/or in the frequency domain (e.g., median frequency) [79,80]. In musicians, EMG analysis has been found to be efficient for detecting muscle fatigue with PRMD players compared to those without PRMD [94].

(i) Efficacy of “Taping” for Muscle Movement Restriction

As above-described, altering the resting position of the scapula due to muscle imbalance can stimulate pain [60]. This pain can be alleviated by taping the scapulae of violinists into a position that prevents excessive elevation and protraction whilst playing. EMG measurements can be used to evaluate the efficacy of taping treatment by recording the activity from the upper trapezii, the scapula retractors and the right sternocleidomastoid muscles.

(j) Biofeedback

The recording of surface EMG is also useful for biofeedback in the treatment of pain problems, and to train players to reduce excessive force, such as that produced in the left hand and wrist of violinists from gripping the neck of the violin too tightly [24].

(k) Assessment of Low Back Pain (LBP)

Using EMG measurements, it has been demonstrated that the presence of low back pain (LBP) can cause a modification of the activation between synergistic muscles of the lumbar back, suggesting that subjects with LBP experience higher fatigability of the erector spinae muscles at the thoracic part than at the lumbar part [96–99]. The increased fatigability of the thoracic part may be relevant in string players whose upper body is active during playing.

4. Posture and Motion

4.1. Significance of Posture and Movement to Playing Disorders 

Information about posture and kinematics can be used for developing efficient and effective strategies to prevent overuse syndrome in violinists, keeping biological loads under physiological limits, focusing on physical economy for minimizing fatigue during training [103,104] and for the assessment of postural flaws [6,60,105,106].

4.2. Measuring Kinematics and Dynamics in Playing

4.2.1 Three-dimensional Motion Analysis

Monitoring the kinematics of the body, violin and bow is accomplished by measuring the time-position of properly attached passive markers using an optoelectronic motion capture system [48]. 

Specific systems include the MacReflex 3D analysis system [15,107] and the Vicon multiple-camera motion capture system [15,58,108]. The three-dimensional time coordinate data are offline reconstructed using a Butterworth filter [56,109]. Angular information can also be obtained from these photogrammetric data [110]. Dynamic modeling using inverse dynamic analysis is used to estimate internal loads at the joints [108,111]. 

4.2.2. Electrogoniometers (twin axis) and Potentiometers (single axis)

Bi-axial electrogoniometers are used to measure the range of wrist motion, to identify frequently assumed wrist positions, and to determine the differences between right and left wrist motions among professional violinists [113,114]. Single-axis potentiometers are used to measure finger movement in double bass players [15,115].

4.2.3. Impact Loading

Intensive, stressful activations of the upper limb during playing result in severe loading on the upper limb from each bowing beat, and are related to progressively increasing harm. The small intrinsic hand muscles, which are greatly involved in generating these recurrent abrupt movements, are thus exposed to risk of damage [116,117]. Similar to the muscles, tendons and nerves of the wrist, the forearm, elbow, shoulder, and neck are at great risk, and repetitive strain injury can take place [13].

4.2.4. Accelerometry

The application of accelerometers to measure movement, especially dynamic movement, can provide detailed information about abrupt dynamic loading, including intensity, timing and frequency content [80]. Although the application of accelerometers in assessing musicians’ movement has up to this point been limited, the potential of this method is promising [126,127,128].

4.2.5. Other Force Measurements and Dynamometry

Forceplate measurements can be used to monitor the foot–ground reaction forces during playing. For instance, in flute playing, two forceplates, one for each foot, can serve to study the shifting effects from one foot to the other following changes in playing technique [102]. Forceplate measurements, together with kinematic and EMG measurements, may also be incorporated into a multi-segment biomechanical model for studying the biomechanics of violin playing [58].

A custom-designed force transducer has been used to monitor the force exerted on the fingerboard of the instrument by the left finger in playing a musical note at diverse playing tempi or other playing conditions [129,130]. This finger force has been used as the input force in a 3D biomechanical dynamic model for the index finger, to simulate the internal tendon and joint forces of the hand [131,132]. 

4.3. Combined Measurements

4.3.1. EMG and Kinematics/Dynamics

Combined measurements of kinematics of the bowing arm and of the EMG of the trapezius and serratus muscles are performed to look for differences between violinists with subacromial impingement syndrome (SIS) and uninjured violinists [70,81,111].

4.3.2. EMG and Acoustic Signals (Sound)

The simultaneous recording of muscle activity and its relationship to sound production as captured by its acoustic signals can be used to study a musical performance of violin playing with vibrato [133]. 

4.4. Multidimensional Signal Analysis (MSA)

Multidimensional signal analysis (MSA) involves the coordination and correlation between data collected through multiple experimental and analytic techniques [47,56,58,59,70,101,107]. 

4.5. Semi-Quantitative Methods Using Visual Assessment, Physical Examination and Questionnaire

Task-specific measures of PRMD, incorporated into qualitative posture assessment and physical examination, have been used in conjunction with questionnaires [2,7,60,106,134].

5. Summary

This review provides a description of the playing-related motor disorders in performing musicians, and of the methodologies used to identify and evaluate these disorders. Methodologies to diagnose, characterize and evaluate PRMD are clearly of importance for the further improvement of devices and techniques aimed at reducing damage associated with the prolonged playing of music.

References