Diferença entre os sexos na razão de ativação muscular relativa do membro superior durante a abdução isométrica do ombro

Abstract

Introduction: Scapulothoracic muscles perform an important role in shoulder’s joint stability, and an uncoordinated activation of the upper girdle muscles can lead to compensations and dysfunctions that may compromise the joint’s function. The high shoulder request during work tasks makes the shoulder pain a common musculoskeletal disorder in general population, with higher prevalence in women. Current findings support that there may be sex differences in shoulder muscles activation, and it is important to understand how some biological mechanisms can support the development of neck/shoulder disorders. Objective: The aim of this study is to identify if there are sex differences in the relative muscle activity ratios of the upper girdle muscles during the shoulder isometric abduction in scapular plane. Hypothesis: It was expected a higher imbalance in the women’s shoulder muscle activation. Methods: 17 asymptomatic females and 17 asymptomatic males were evaluated, who were between 18 and 35 years old, without musculoskeletal symptoms in the neck/shoulder according to Nordic Musculoskeletal Questionnaire (NMQ) and did not have neck/shoulder pain higher than 2cm in the Visual Analogue Scale in the last 3 months. The torque peak (PT) and the steadiness of the submaximal torque at 20% and 35% of the PT were evaluated by isometric abduction of the dominant upper limb in the scapular plane. Surface electromyographic from upper, middle and lower trapezius (UT, MT, LT), serratus anterior (SA) and anterior deltoid (AD) were recorded. The relative muscle activity ratios analysis was obtained from the Root Mean Square (RMS) values and then expressed as: UT/MT, UT/LT, UT/SA, LT/SA, AD/MT, AD/LT, AD/SA, AD/MT+LT+SA and AD/LT+SA. Statistical analysis: Statistical analysis was performed using SPSS software (Statistical Package for Social Science, version 17) through repeated-measures analysis of variance, with a significant level of 5%. Results: It was found main sex effect for the AD/LT ratio. Men prensented higher values than women (men < 1; women > 1). There was also main intensity effect for the LT/SA, AD/LT and AD/LT+SA ratios, showing that changes on intensity also changed the ratios. Conclusion: Men presented higher AD activation, demonstrating more precise motor control than women, since AD is the task effector’s muscle.