Effects of Cervicothoracic Junction Manipulation on Shoulder Strength and Electromyography Amplitude in Asymptomatic Adults

PURPOSE: Recent studies have examined the relationship between spinal mobility restriction and upper quadrant muscle function in patients with shoulder pain with limited results. Little research has been conducted to examine the effects of cervicothoracic junction manipulation (CTJ) on shoulder strength and electromyography (EMG). The primary purpose of this study was to examine the immediate and carry-over effects of CTJ manipulation on shoulder strength of shoulder abduction (ABD) and external rotation (ER), as well as EMG amplitude of the anterior deltoid (ADELT), mid-deltoid (MDELT), supraspinatus (SUPR), and infraspinatus (INFR) muscles. The secondary purpose was to determine the reliability of the strength and EMG testing protocol used in the study. METHODS: Twenty-four adults (7 men, 17 women, aged 29.8 +/- 9.8 years) were randomly assigned into two groups: manipulation group that received a sham CTJ manipulation (3 men, 9 women). A hand-held dynamometer (HHD) was used to determine shoulder strength, and EMG activity was recorded using a wired EMG unit and four tethered surface electrodes. Shoulder ABD and ER strength and EMG activity of the ADELT, MDELT, SUPR, and INFR muscles were collected simultaneously during maximal voluntary isometric contraction (MVIC) of shoulder ABD and ER. Two trials of MVIC were performed for shoulder ABD and ER, and the average of the two trials was used for statistical analysis. All participants were asked to come in two separate days. The within-day and between-day reliability of shoulder strength and EMG measurements was determined in the first two visits. The intervention was delivered during the second visit, which was within 24-48 hours of the first visit. To assess immediate and carry-over effects of CTJ manipulation (either manipulation or sham manipulation), the shoulder strength and EMG were collected before intervention, immediately post intervention, 15 minutes post intervention, and 30 minutes post intervention. To assess within-day intra-tester reliability, the shoulder strength and EMG activity were collected twice on the first visit, and again during the second visit before the intervention to determine the between-day reliability. Outcome measures consisted of shoulder abduction and ER strength in kilograms*force (kgf) and EMG root mean square (RMS) of the ADELT, MDELT, SUPR, and INFR muscles. Intra-class correlation coefficients (ICC) were used to determine intra-tester within-day and between-day reliability. Six separate 2x4 ANOVAs with repeated measures were used to analyze HHD and EMG data for between and within group comparison. Alpha level was set at 0.05 for all analyses. RESULTS: The results showed excellent within-day and between-day reliability for both HHD and EMG measurements (within-day reliability: ICC = 0.97-0.99 for HHD, ICC = 0.97-0.99 for EMG, and between-day: ICC = 0.96-0.99 for HHD, ICC = 0.94-0.96 for EMG). The ANOVA results revolted a significant group by time interaction for ER strength (p = 0.047), EMG RMS of SUPR (p = 0.041), and EMG RMS of INFR (p = 0.001), but not for shoulder ABD strength or the rest of the EMG data. Post-hoc analysis showed a significant decrease (p CONCLUSIONS: The results of this study suggest that a potential immediate inhibition carryover effect exists on shoulder EMG and HHD for shoulder ER post spinal manipulation and is possibly maintained for a period up to 30 minutes post technique.