Let´s Swing it -The Interaction Between Participation-Related Shoulder Load and Pre-season Trunk Rotation Power on Shoulder Problems in Male Handball Players.

Background: Little is known about the influence of kinetic chain strength and power on shoulder problems in handball players or the impact of participation-related shoulder load (PSL) during a season. Suboptimal activity of the kinetic chain during throwing might make the shoulder more vulnerable.

Purpose: The purpose of this study was to assess 1) the association between pre-season measurements and shoulder problems among handball players and 2) whether pre-season strength and power influence the association between PSL and severity of shoulder problems.

Study design: Prospective observational cohort study.

Methods: Pre-season measurements were done using the Isometric mid-thigh pull for lower body strength, a seated test for trunk rotation power (TRP) and isometric testing of external (ER) and internal rotation shoulder strength on 42 male players. Shoulder problems (prevalence, substantial prevalence, and severity score) were documented weekly through a season (31 weeks) with The Oslo Sports Trauma Research Center Overuse Questionnaire (OSTRC-O2) and PSL with the modified Borg rate of perceived exertion scale. Spearman´s correlation coefficient was applied to examine the association within the first aim, while a mixed model ANOVA was conducted to analyze the second aim.

Results: A weak and negative correlation (rs=-0.34) was found between pre-season ER strength and the individual prevalence of shoulder problems (p=0.029). A main effect was found between PSL and the OSTRC-O2 severity score (p=<0.001) with higher severity scores observed with increased PSL. A significant interaction was found between PSL and pre-season TRP regarding their influence on the OSTRC-02 severity score (p=0.017). With higher PSL, a higher severity score was observed among players with pre-season TRP more than one standard deviation below the group's mean.

Conclusions: The results indicate that low TRP may make the throwing shoulder more vulnerable to an increase in load. Looking beyond shoulder strength and load may therefore be important.

Level of evidence: 3.