Electromyographic analysis of trunk and lower extremity muscle activities during pulley-based shoulder exercises performed on stable and unstable surfaces

[Purpose] The aim of the present study was to identify the effects of an unstable supportsurface (USS) on the activities of trunk and lower extremity muscles during pulley-basedshoulder exercise (PBSE). [Subjects] Twenty healthy college students were included in thisstudy. [Methods] Surface EMG was carried out in twenty healthy adult men. The activitiesof trunk and lower extremity muscles performed during PBSE using a resistance of 14 kg ona stable or unstable support surface were compared. The PBSE included shoulder abduction,adduction, flexion, extension, internal rotation, and external rotation. [Results] On theunstable surface, the rectus abdominis and erector spinae showed significantly lessactivation during shoulder external rotation, but the extent of activation was notsignificantly different during other shoulder exercises. The external oblique and rectusfemoris showed no significant difference during any shoulder exercises. The tibialisanterior showed significantly greater activation during all shoulder exercises, exceptflexion and extension. The gastrocnemius showed significantly greater activation duringshoulder abduction, extension, and internal rotation. However, during shoulder adduction,flexion, and external rotation, the gastrocnemius showed no significant difference.[Conclusion] The use of USS to increase core stability during PBSE is probably noteffective owing to compensatory strategies of the ankle.Key words: Electromyography, Core stability, Ankle strategy