Physical Adaptations in Adolescent Swimmers: Implications for Injury Prevention

This week’s EXSS Impact post highlights the work being done to prevent musculoskeletal injury during sport and physical activity.  We thank Elizabeth Hibberd along with her dissertation committee (Joseph Myers (Advisor), David Berkoff, Kristen Kucera, Kevin Laudner, Bing Yu) for providing this week’s content, which highlights her work to prevent injury in swimmers.

1) Why did you do the study?

swimCompetitive youth swimmers train 11 months out of the year and perform approximately 6,000-7,000 yards per practice during the training season1 with little rest and time for muscle recovery from repetitive microtrauma. Due to these high levels of training, it is hypothesized that physical characteristics of swimmers’ upper extremities adapt to the demands that are placed on them and predispose them to “swimmer’s shoulder,” which is the general term for overuse injury in swimming athletes. Interfering shoulder pain has been reported in 45-87% of swimmers during their careers. Our previous work with competitive youth swimmers found that 85% of swimmers believe that mild shoulder pain is normal and should be tolerated in order to complete the necessary yardage, with 72% of the swimmers reporting use of pain medication (either prescribed or over-the-counter) in order to participate. The prevalence of shoulder injuries and the beliefs regarding shoulder pain in youth swimmers highlight the need for an effective assessment tool and intervention program to be validated for youth swimmers.

Clinically, athletic trainers treat a high percentage of swimmers reporting for treatment of shoulder pain during the training season. Due to the high training load, it is hypothesized that physical characteristics of swimmers change due to participation factors and predispose the athlete to shoulder pain and injury. Theoretically, large amounts of swim training would result in increased stress on the shoulder and manifests as adaptations in physical characteristics that may predispose the athlete to injury (Line A). These identified intrinsic and extrinsic factors may predispose the athlete to the development of swimmer’s shoulder (Line B) causing shoulder pain and dysfunction (Line C) and ultimately resulting in time loss due to injury (Line D). These alterations are hypothesized to develop due to the training load, but research is needed to determine the effect of swim training on these physical characteristics that may be causative of impingement and the development of swimmer’s shoulder.

lizzie model

Theoretical Model of the Development of Shoulder Pain and Injury

Although previous literature has suggested that shoulder physical characteristics change with high loads of swimming, a prospective evaluation of these characteristics is necessary to determine if they truly are affected by swimming participation. Therefore, the purpose of this project is to prospectively identify the effect of the training season on physical characteristics and shoulder pain and the relationship between participation factors and each of the physical characteristic variables in competitive youth swimmers. Evaluating these changes in the physical characteristics in competitive swimmers and their relationship to participation variables will advance the understanding of the effects of swim training on physical characteristics and provide support for future studies focusing on injury prevention programs and practice recommendations. In addition, evaluating how the physical characteristics change during the training season and their relationship with shoulder pain/functional scales and cumulative yardage, a screening tool can be developed to identify at risk individuals as well as provide information regarding the development of intervention programs and practice guidelines for competitive swimmers.

2) What did you do and what did you find?

A cohort repeated measures research design with a non-overhead athlete control group and a competitive swimming groups was utilized in the current study. All participants in the study participated in three data collections: pre training season, mid training season (approximately 6 weeks), and post-training season (approximately 12 weeks). At each testing session, data collection occurred prior to the start of a team practice and participants filled out a demographics questionnaire and completed a physical exam that included measures of posture, subacromial space distance, and pectoralis minor length.

shoulder-painAt baseline screening (before intense swim training began), there were no clinically significant differences in swimmers and non-overhead athletes on forward head and shoulder posture, normalized pectoralis minor length, normalized subacromial space distance, internal/external rotation ROM, and posterior shoulder tightness. While there were no significant differences in forward hand and shoulder posture between the groups, both groups demonstrated forward shoulder and head posture beyond reported norms. These findings indicate that many physical characteristics that are observed in swimmers are not swimming specific. Our findings indicate that, high-school students presented with forward shoulder posture that develops due to lifestyle factors such as computer use, video games, and desk ergonomics. These alterations in posture can lead to upper extremity injury, but also back pain and respiratory issues. Factors other than swimming participation, such as school and technology use, play an important role in the adaptation of physical characteristics. These findings highlight the importance of interventions during the school day and personal time to improve posture.

Over the course of the training season, swimmers experienced a significant decrease in subacromial space distance and external ROM and a significant increase in forward shoulder posture, potentially making the athlete more vulnerable to the development of shoulder pain and injury. Over the course of the training season, swimmers develop risk factors that may be causative of impingement and the development of swimmer’s shoulder. These findings indicate the importance of implementing an injury prevention program in competitive swimmers designed to strengthen the posterior scapular stabilizing musculature and stretch the anterior musculature. Improvements in these areas would improve scapular functioning and control, thus improving subacromial space distance and forward shoulder posture and ultimately decreasing shoulder pain and injury in competitive swimmers. The findings of this study also highlight the importance of understanding the role of participation factors in contributing to changes in physical characteristics and future studies that focus on maximizing performance while minimizing injury risk.

3) What’s the impact of these findings on the public?

opparmlegThe significant changes in the physical characteristics that are seen in competitive swimmers during the training season compared with changes in non-overhead athletes and the relationships between total yardage and pain scores indicate that the training season clearly has a substantial influence on physical characteristics that may lead to shoulder pain and injury. These findings highlight the interplay of intrinsic and extrinsic risk factors that may be occurring. The development of shoulder pain and injury in swimmers is multifactorial due to a combination of both intrinsic and extrinsic risk factors. When athletes present with certain intrinsic risk factors, they become predisposed to injury. However, without exposure to extrinsic risk factors (participation factors), the athlete is unlikely to develop an overuse injury. With the presence of extrinsic risk factors, the athlete is susceptible to the development of shoulder pain and injury. Through repeated exposures, without the presence of a diagnosed injury, the modifiable intrinsic risk factors that swimmers are continually changing due to adaptations of the shoulder during swim training. These adaptations and exposure to extrinsic risk factors may cause the susceptible athlete to develop shoulder pain or injury. Future research needs to focus on understanding each of intrinsic and extrinsic risk factors and the relationships between them in order to created evidence-based swim training, dry-land, weight training, and injury prevention program that maximize performance while minimize injury risk.