The shoulder joint is the second most affected body part of all overuse injuries in overhead athletes. Due to the repetitive throwing motion overhead athletes show the following characteristic adaptations of their dominant shoulder: Loss of internal rotation (IR) and gain of external rotation (ER), reduced muscle strength of the shoulder external rotators and scapular dyskinesis. On the one hand these adaptations are normal and necessary for a powerful throwing performance. On the other hand the amount of adaptation seems to play a crucial role in developing overuse symptoms and therefore becoming a risk factor. Most previous studies investigating throwing specific adaptations and risk factors focused on overhead sports like baseball, handball or tennis, whereas similar research in volleyball is still insufficient. Therefore the aim of this study is to evaluate if sport specific adaptations are present in female volleyball players and if yes, if there is a difference of the extent of these adaptations in volleyball players with overuse symptoms and players without.

Background The shoulder joint is the second most affected body part of all overuse injuries in overhead athletes.Prevalence of a history of shoulder problems related to overuse in volleyball players was reported to be approximately 60%. Typical overuse symptoms like pain seriously limit progress in performance and the individual career options of volleyball players.

Due to the repetitive throwing motion overhead athletes show the following characteristic adaptations of their dominant (Ds), compared to the non-dominant (NDs) shoulder: 1) Loss of internal rotation (IR) and gain of external rotation (ER), by preserving the total rotational motion (TROM). 2) Reduced muscle strength of the shoulder external rotators (ER). 3) Scapular dyskinesis. On the one hand these adaptations are normal and necessary for a powerful throwing performance. On the other hand the amount of adaptation seems to play a crucial role in developing overuse symptoms and therefore becoming a risk factor; e.g. loss of IR, also known as glenohumeral internal rotation deficit (GIRD) of more than 20° side difference, and a loss of TROM of the Ds, were defined as risk factors in baseball players. Moreover decreased muscle strength of ER (OR: 0.71 per 10N decrease) in the Ds as well as obvious scapular dyskinesis were associated with increased risk of overuse related shoulder symptoms (ORSS). Nevertheless there are still overhead athletes showing these adaptations or risk factors without being symptomatic.

Recently, several authors underlined the importance of core stability related to the kinetic chain during an overhead throwing task. It is hypothesised that symptomatic athletes may overload the shoulder girdle through altered biomechanics in an effort to compensate for insufficient power generated by the core musculature. The most reliable measurements to asses core stability components are core endurance tests.

Most previous studies investigating throwing specific adaptations and risk factors focused on overhead sports like baseball, handball or tennis, whereas similar research in volleyball is still insufficient. Moreover, no one ever investigated core endurance and its possible association with (ORSS) in volleyball players.

Objective The first aim is, to evaluate if sport specific adaptations such as IR ROM deficit, gain of ER ROM, ER strength deficit, alterations in TROM and scapular dyskinesis are present in female volleyball players and if yes, if there is a difference of the extent of these adaptations in volleyball players with ORSS and players without.

The second aim is, to evaluate if there is a difference in core endurance in volleyball players with ORSS and players without and if there is a correlation of core endurance and shoulder related risk factors such as ER strength deficit and scapular dyskinesis?

Inclusion Criteria:

• female
• being member of a Nat. League B/Nat. League A Volleyball Team in season 2017/2018
• minimum age 16 years
• sufficient understanding/speaking of the German language
• signed informed consent

Exclusion Criteria:

• having had any surgery at the shoulder joint of the dominant or non- dominant side within last six month
• having had any self reported trauma at the shoulder joint of the dominant or non-dominant side, which limits training or match participation of more than 50%
• limitation of more than 50% in training or match participation caused by a surgery or trauma at the core or lower extremity

female volleyball players from the German part of Switzerland