Arm Elevation Angle And Contraction Intensity Effects On Scapular Position During Scapular Plane Isometric Contractions

Abstract

PURPOSE: The purpose of this investigation was to examine the effects of arm elevation angle and voluntary isometric contraction intensity on scapular position, between healthy young and older adults. METHODS: Fourteen young adults (YA) (23.2 ± 2.5 yrs) and 13 older adults (OA) (58.6 ± 6.8 yrs) performed maximal and sub-maximal isometric arm abduction contractions in the scapular plane on a Biodex isokinetic dynamometer. The scapular plane was estimated by placing the subjects' arm in an abducted position 45 degrees between the frontal and sagittal planes, in the transverse plane. Subjects performed five isometric maximal voluntary contractions (MVCs), followed by randomly ordered ten-second sub-maximal contractions at 10–90% MVC (10% increments), at the following arm abduction angles (AA): 30°, 60° and 90°. Scapular position (SP) was determined immediately before and during each contraction with a digital inclinometer. RESULTS: The scapula assumed a more upward rotated orientation with increasing AA. During all maximal and sub-maximal contractions, the scapula assumed a less upwardly rotated orientation than during just prior to the contraction. The results from a repeated measures ANVOA demonstrated a significant AA (F2,50 = 54.56, p<0.001) and CI(F10,250 = 51.01, p<0.001) main effect on SP, and an AA by CI interaction (F20,500 = 2.39, p=0.001). Although the older adults (5.1±0.9°) had a lower SP than the young adults (6.9±0.9°), the group main effect was not significant (F1,25= 1.88, p=0.183). No differences in SP were seen between the groups in the resting condition at all AA positions. Differences in SP were seen between the groups at the 90° AA position during the MVC. Multiple regression analysis revealed an R2 statistic for the regression model of 0.46; R2 change for AA (0.35), CI (0.10) and group (0.01) all regression coefficients were statistically significant (p<0.001). Separate multiple regressions performed on YA and OA revealed similar regression coefficients for CI (−0.08). However, the coefficients for AA were different, YA (0.22) and OA (0.15). CONCLUSIONS: Scapular position during isometric abduction contractions is dependant upon the position of the arm as well as intensity of the contraction. Overall, there appears to be no differences between YA or OA in SP.