YANAI, T., J. G. HAY, and G. F. MILLER. Shoulder impingement in front-crawl swimming: I. a method to identify impingement. Med. Sci. Sports Exerc., Vol. 32, No. 1, pp. 21–29, 2000.
Purpose: The impingement of subacromial structures has been proposed as a major cause of the shoulder problems experienced by athletes who use repetitive overhead actions. The purpose of this study was to develop a noninvasive method to identify instances at which the shoulder was experiencing impingement during front-crawl swimming.
Methods: Shoulder impingement has been reported to occur when an arm is: (a) elevated above shoulder height while being rotated internally; and (b) forcibly elevated at, or beyond, the maximum active elevation angle. In this study shoulder configurations that satisfied the above two conditions were sought throughout the functional range of each shoulder; and a boundary that distinguished configurations that would cause shoulder impingement was defined. The shoulder movements exhibited during performance of the front-crawl stroke were measured using three-dimensional videography and compared with the boundary defined for each shoulder. The shoulder was considered to experience impingement if the shoulder configuration observed exceeded the boundary defined for that shoulder.
Results: For a male collegiate swimmer, impingement occurred for 12% of the stroke time for each shoulder.
Conclusions: The analysis permitted the identification of the instances at which the shoulders were experiencing impingement during the front-crawl swimming. In this study, the measurement of the boundary was based entirely upon the mechanism of impingement described in the literature. Further studies are needed to confirm the occurrence of impingement by means of advanced visualization techniques, such as magnetic resonance imaging (MRI) and ultrasonogram.
Shoulder pain has been frequently reported by competitive swimmers, particularly by those who use the freestyle and butterfly strokes. Surveys have shown consistently that 40–70% of elite swimmers complained of shoulder pain (8,10,24). Although the etiology of the shoulder pain has not been understood completely, impingement of the subacromial structures has been hypothesized as a major cause of the shoulder problems experienced by front crawl swimmers (5,15,16,19,22,24). The impingement refers to the mechanical phenomenon in which contact between the greater tuberosity of the humerus and the acromial arch creates compressive force on the subacromial structures. Pathological conditions such as bursitis and rupture of rotator cuff tendon are believed to develop when the magnitude of the compressive force is sufficiently large and the impingement is repeated over several years. This pathological condition of the subacromial structures was defined as impingement syndrome (20). The mechanism of impingement syndrome has also been cited frequently to explain the cause of shoulder injuries experienced by athletes who participate in throwing activities (2,11,13,22,26,27). There is as yet, however, no biomechanical evidence to demonstrate that shoulder impingement occurs in such athletic activities. The purpose of this study, therefore, was to develop a noninvasive method to identify instances at which the shoulder experienced impingement during front-crawl swimming.