Title : Hug-Up and Hug-Off: Novel physical examination tests for supraspinatus and infraspinatus assessment
Abstract:
Aim/Background: Accurate physical examinations are essential for diagnosing shoulder pathologies, particularly rotator cuff injuries. Evaluating muscle activation patterns can enhance diagnostic accuracy and inform clinical practices. Electromyography (EMG) is widely used, with two primary methods: surface EMG (sEMG) and fine-wire EMG. While fine-wire EMG offers high-resolution recordings of deep muscles, it is invasive, uncomfortable, and less suited for dynamic testing. In contrast, sEMG is non-invasive, suitable for dynamic movements, and allows broader participant inclusion with natural shoulder motion. Although sEMG signals may be influenced by adjacent muscles, advancements in electrode placement and signal processing have improved specificity and reliability. This study employs sEMG to analyze muscle activation during shoulder exams, aiming to optimize diagnostic protocols while ensuring participant comfort and data accuracy.
Methods: Thirty healthy volunteers were recruited. sEMG recorded muscle activity during tests targeting the supraspinatus (Jobe, Full Can, Palm Up, Whipple, 0° Internal Rotation Resistance, 0° Neutral Resistance, 0° External Rotation Resistance, Forward Flexion Resistance, Hug-Up) and the infraspinatus/teres minor (including ABIR, Hug-Off, and other clinical tests). Participants performed fixed 1kg resistance tests and maximal voluntary contraction (MVC) tasks across varying arm positions. To ensure comprehensive data and reduce inaccuracies from muscle synergy, electrodes were placed on the supraspinatus, infraspinatus, anterior deltoid, middle deltoid, posterior deltoid, and teres minor. This enabled precise monitoring of individual muscle contributions while minimizing compensatory activation from adjacent muscles. Root Mean Square (RMS) values of sEMG signals quantified muscle activation, and data were compared across tests and muscles to assess activation patterns.
Results: Distinct RMS variations were observed among the tests. Jobe and Full Can elicited high RMS values in the supraspinatus, but Hug-Up demonstrated the most consistent and specific activation, minimizing deltoid interference. For the infraspinatus and teres minor, Hug-Off provided the most sensitive and specific activation compared to ABIR and other clinical tests, with higher RMS values and reduced non-target muscle activity. RMS comparisons showed Hug-Up and Hug-Off offered the highest sensitivity and specificity for the supraspinatus and infraspinatus, respectively.
Conclusion: sEMG analysis offers valuable insights into muscle activation during shoulder exams. Hug-Up is the most sensitive and specific test for assessing supraspinatus function, while Hug-Off is optimal for evaluating infraspinatus activation. These findings can refine examination techniques, enhancing diagnostic accuracy and guiding targeted rehabilitation protocols for rotator cuff injuries.
Keywords: Shoulder, Surface Electromyography, Physical Examination, Rotator Cuff, Muscle Activation, Diagnosis
