Shoulder characteristics in weight trainers
Injuries related to weight training has increased during the past decade, with 36% of weight training related injuries and disorders occurring at the shoulder joint (Goertzen et al., 1989; Keogh et al., 2006). 25-30% of the individuals participating in weight training have reported injuries sever enough to seek medical help (Jones et al., 2000; Powell et al., 1998).
Weight training places stress on the shoulder by requiring a conventionally non-weight bearing joint to bear significant loads during the course of repetitive lifting (Kolber et al., 2009). Traditional weight training exercises have been shown to create muscular imbalances and predispose the shoulder to injury by placing the joint in biomechanical unfavorable positions, such as bottom of ROM external rotations (Gross et al., 1993). Furthermore, programs biased toward specific bodyparts generally place emphasis on developing the large primary movers while neglecting the smaller stabilization muscles required for mobility, balance, and unimpaired shoulder function (Barlow et al., 2002).
Kolber et al. (2009) tested the shoulder muscular strength, function, and mobility of 90 experienced male weight trainers compared to a sedentary population. The researchers reported significantly greater strength among weight trainers of the abductors, internal rotators, and upper trapezius fibers. The greater strength values are because typicall training programs target the deltoids, upper trapezius, and internal rotators (pectoralis and latissimus dorsi). The strength of the external rotators and lower trapezius, however, were not different than the sedentary population. The imbalance in strength between internal/external rotators, abductor/external rotator, and upper/lower trapezius fibers illustrates the training induced strength imbalances between muscle groups that normally function together to execute a movement.
There is significant evidence that individuals with shoulder disorders possess greater deficits in external rotation strength compared to internal rotation strength (MacDermid et al., 2004; Reddy et al., 2000; Tata et al., 1993; Wang & Cochrane, 2001; Warner et al., 1990). During over head pressing movements, the external rotators function together with the deltoid to effective elevate the arm over head. Imbalances created by exercise programs that emphasize the deltoid and neglect the external rotators often result in altered muscle coordination, redistricted range of motions, and shoulder impingement (Kolber et al., 2009). Insufficient muscle strength of the lower trapezius fibers have also been linked to shoulder impingement (Cools et al., 2007).
Weight training can also result in mobility dysfunctions. Bodybuilders display a decreased active range of motion among shoulder flexion, abduction, and internal rotation, compared with excessive external rotation ROMs. Additionally, there are greater restriction on the posterior soft tissue due to internal rotation loss and lack of exercises or stretching that improves the flexibility of the posterior joint capsule (Kolber et al., 2009; Wang & Cochrane, 2001; Warner et al., 1990). Furthermore, posterior shoulder tightness may be responsible for limited mobility, resulting in glenoid labrum detachment and impingement syndromes (Bach & Golberg, 2006).
Kolber demonstrated that traditional weight training programs do not include the exercises necessary to strengthen the stabilization muscles required during normal shoulder function. Additionally, emphasizing only the large movers such as the pectoralis, latissimus dorsi, and deltoids creates a strength and flexibility imbalance at the shoulder joint. Encorporating exercises that strengthen the external rotator cuff muscles and scapular fixation musculature along with select flexibility exercises for internal rotation and the posterior capsule should: balance strength ratios needed for coordinated shoulder function; increase soft tissue flexibility balance as required for normal shoulder mobility; improve the strength of the humeral head depressors thus helping to prevent impingement with over head exercises; and, reduce the more common risk factors associated with shoulder disorders.
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