Power spectra of sternocleidomastoids, splenius capitis, and upper trapezius in oblique exertions

Abstract

BACKGROUND CONTEXT: There is relatively little known concerning the spectral profile of the cervical muscles, despite the fact that neck injury and pain are quite prevalent. PURPOSE: The objective of the study was to calculate and study the power spectral characteristics of the sternocleidomastoids, splenii capitis and upper trapezii in anterolateral flexion and posterolateral extension in a ramp contraction. STUDY DESIGN/SETTING: In a laboratory setting experiments were conducted to record surface electromyographic (EMG) data from six cervical muscles and power spectral variables obtained. PATIENT SAMPLE: Forty normal and healthy young adults (21 men, 19 women). OUTCOME MEASURES: Power spectral of EMG signals. METHODS: EMG data for the left and right isometric anterolateral flexion and posterolateral extension were acquired from the sternocleidomastoids, splenii capitis and upper trapezius bilaterally. The subjects were seated in an upright posture and exerted left and right anterolateral flexor and posterolateral extensor efforts from rest to their maximal voluntary contraction in a gradual linear ramp fashion using visual feedback as a guide. The force exerted and the surface EMG data were sampled at 1 kHz at every 10th percentile grade of contraction and the EMG data were subjected to the Fast-Fourier transform analysis. The median frequency (MF), mean power frequency (MPF), peak power and total power of all six cervical muscles were analyzed. RESULTS: In the anterolateral flexion the ipsilateral sternocleidomastoid and splenius capitis had a wider band of frequency, which further widened with increasing grade of contraction. The trapezius did not engage in the same manner or to the same magnitude. The MF of the sternocleidomastoid in the anterolateral flexion in both genders progressively increased, the splenius capitis remained relatively unchanged, and the upper trapezius declined with the increasing grades of contraction. CONCLUSIONS: There is no significant difference between the genders in spectral profile. There is a bilateral symmetry in spectral profile with reference to activity; however, they are significantly different in different activities for the same muscles. With increasing magnitude of contraction power, spectral density distribution increases and the median frequency decreases. These results can serve as a useful reference for painful necks. Restoration of power spectral characteristics may indicate normalcy, which cannot be gleaned by other EMG or force variables.