Abstract
Altered scapular muscle activity is mostly described under unloaded and submaximal loaded conditions in impingement patients. However, there is no clear evidence on muscle activity with respect to movement phases under maximum load in healthy subjects. Therefore, this study aimed to investigate scapular muscle activity under unloaded and maximum loaded isokinetic shoulder flexion and extension in regard to the movement phase. Fourteen adults performed unloaded (continuous passive motion [CPM]) as well as maximum loaded (concentric [CON], eccentric [ECC]) isokinetic shoulder flexion (Flex) and extension (Ext). Simultaneously, scapular muscle activity was measured by EMG. Root mean square was calculated for the whole ROM and four movement phases. Data were analyzed descriptively and by two-way repeated measures ANOVA. CPMFlex resulted in a linear increase of muscle activity for all muscles. Muscle activity during CONFlex and ECCFlex resulted in either constant activity levels or in an initial increase followed by a plateau in the second half of movement. CPMExt decreased with the progression of movement, whereas CONExt and ECCExt initially decreased and either levelled off or increased in the second half of movement. Scapular muscle activity of unloaded shoulder flexion and extension changed under maximum load showing increased activity levels and an altered pattern over the course of movement.
Highlights
For functional shoulder movements especially overhead, well-coordinated scapular motion is essential (Inman et al 1944; Kibler 1998; Ludewig and Reynolds 2009)
Activity levels were significantly higher during shoulder flexion than during extension, except for lower trapezius (LT) in continuous passive motion (CPM)
Scapular muscle activity pattern of unloaded shoulder flexion and extension movements changed under maximum loading conditions
Summary
For functional shoulder movements especially overhead, well-coordinated scapular motion is essential (Inman et al 1944; Kibler 1998; Ludewig and Reynolds 2009). While some studies found an altered scapular muscle activity under unloaded and submaximal loaded conditions in impingement patients, it is still unclear to which extent these differences are evident under maximum load and if they occur in equivalent phases of arm movement. This has to be emphasized since higher loads and repetitive overhead movements put the shoulder at risk for complaints in athletes and employees who have to work overhead (Hagberg and Wegman 1987; Lo et al 1990; McMaster and Troup 1993; Bernard 1997; Pluim et al 2006). It will be evaluated whether differences in muscle activity are dependent on the movement phase
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