Posture and isokinetic shoulder strength in female water polo players

Abstract

Water polo is a high-intensity intermittent aquatic sport which places large physical demands on the participants [1] and involves repetitive physical motions that are common to swimming and baseball pitching. [2] Water polo consists of four quarters, where two teams of seven players per side attempt to score goals by throwing the ball into their opponents' goal. Water polo is played in a pool measuring either 20 m by 10 m or 30 m by 20 m, with a depth of 1.8 m. During the throwing action, the mechanics are similar to those of baseball pitching. [2] This forms a large component of the sport and involves the combination of muscle strength and coordination between the upper-and lower extremities. However, as the sport is played in a pool, unlike baseball or cricket, there are no stabilising surfaces [3] from which to throw the ball. This, in turn, may increase the total forces on the joints at the shoulder complex. [2] Water polo players continuously place their shoulder joints under recurring stress while performing repetitive overhead movements which can cause joint instability and muscular imbalances between the internal rotator (IR) and external rotator (ER) muscles. [2,4] Radaelli et al. [5] claims that this imbalance may occur due to the more frequent contraction pattern of the IR muscles compared to the ER muscles. The cumulative loads placed on the posterior shoulder joint during deceleration during throwing in water polo can result in posterior stiffness associated with a greater imbalance between the internal and external rotator cuff muscles and translation of the humeral head, thus predisposing the athlete to shoulder injury. [2] Furthermore, during freestyle swimming in water polo, the head is more often out of the water and the ball positioned directly in front of the athlete [2,6] which places a heavy load on the shoulder joint and surrounding soft tissue. [7] In addition, while swimming freestyle in water polo, the dominant stroke action is that of head-up. This requires an altered form of traditional freestyle with the head out of the water and the arm elevation more exaggerated, as the arms are keeping the ball in front of the face of the player. Furthermore, to increase the force of the throw when shooting, a greater amount of external rotation and abduction are required, [6,8,9] enabling females for example to reach a speed to 16.8m/s. [10] The amount of strength required to perform these forceful movements predispose the shoulder region to instability and muscle imbalance between the internal and external shoulder rotators. [11] Lynch et al. [12] reported that swimmers and overhead athletes often develop swimmer's shoulder which encompasses a variety of pathological injuries, such as rotator cuff tendinitis, shoulder instability and shoulder impingement. A disparity in muscle balance may lead these athletes and swimmers to develop an increased risk of postural abnormalities and subsequently, to predispose them to shoulder injuries. However, there is limited evidence regarding the presence of muscle imbalances and postural abnormalities in water polo players. It has been established that if a malalignment in the posture is present, it may indicate that there is a muscle imbalance; thus postural orientation may play a role in sport performance. [13] A study by Gradidge et al. showed that there is a relationship between poor shoulder posture and shoulder injury in water polo players. [14] The limited research into posture and shoulder muscle strength in water polo players makes this study important in assisting with the identification of these muscle imbalances and specific postural characteristics, which will be useful in future studies. Background: Being overhead athletes, water polo players can