Original Article

HSS Journal

, Volume 7, Issue 1, pp 21-28

First online:

A Spectral Analysis of Rotator Cuff Musculature Electromyographic Activity: Surface and Indwelling

  • Sherry I. BackusAffiliated withDepartment of Rehabilitation, Leon Root MD, Motion Analysis Laboratory, Hospital for Special Surgery Email author 
  • , Daniel P. TomlinsonAffiliated withDepartment of Orthopaedic Surgery, Crystal Run Healthcare
  • , Bavornrat VanadurongwanAffiliated withDepartment of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University
  • , Mark W. LenhoffAffiliated withDepartment of Rehabilitation, Leon Root MD, Motion Analysis Laboratory, Hospital for Special Surgery
  • , Frank A. CordascoAffiliated withSports Medicine and Shoulder Service, Department of Orthopaedic Surgery, Hospital for Special Surgery
  • , Eric L. ChehabAffiliated withDepartment of Orthopaedic Surgery, Illinois Bone and Joint Institute
  • , Ronald S. AdlerAffiliated withDepartment of Radiology and Imaging, Division of Ultrasound and Body CT, Hospital for Special Surgery
  • , R. Frank HennIIIAffiliated withHospital for Special Surgery
  • , Howard J. HillstromAffiliated withDepartment of Rehabilitation, Leon Root MD, Motion Analysis Laboratory, Hospital for Special Surgery

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Electromyography (EMG) of the shoulder girdle is commonly performed; however, EMG spectral properties of shoulder muscles have not been clearly defined. The purpose of this study was to determine the maximum power frequency, Nyquist rate, and minimum sampling rate for indwelling and surface EMG of the normal shoulder girdle musculature. EMG signals were recorded using indwelling electrodes for the rotator cuff muscles and surface electrodes for ten additional shoulder muscles in ten healthy volunteers. A fast Fourier transform was performed on the raw EMG signal collected during maximal isometric contractions to derive the power spectral density. The 95% power frequency was calculated during the ramp and plateau subphase of each contraction. Data were analyzed with analysis of variance (ANOVA) and paired t tests. Indwelling EMG signals had more than twice the frequency content of surface EMG signals (p < .001). Mean 95% power frequencies ranged from 495 to 560 Hz for indwelling electrodes and from 152 to 260 Hz for surface electrodes. Significant differences in the mean 95% power frequencies existed among muscles monitored with surface electrodes (p = .002), but not among muscles monitored with indwelling electrodes (p = .961). No significant differences in the 95% power frequencies existed among contraction subphases for any of the muscle–electrode combinations. Maximum Nyquist rate was 893 Hz for surface electrodes and 1,764 Hz for indwelling electrodes. Our results suggest that when recording EMG of shoulder muscles, the minimum sampling frequency is 1,340 Hz for surface electrodes and 2,650 Hz for indwelling electrodes. The minimum sampling recommendations are higher than the 1,000 Hz reported in many studies involving EMG of the shoulder.


shoulder rotator cuff electromyography isometric contraction