Sex Differences in Dynamic Closed Kinetic Chain Upper Quarter Function in Collegiate Swimmers

Context:

Upper quarter injuries have a higher incidence in female swimmers; however, to date, there are few ways to assess the basic functional ability of this region. The upper quarter Y balance test (YBT-UQ) may assist in this process because it was developed to provide a fundamental assessment of dynamic upper quarter ability at the limit of stability.

Objective:

To examine how sex affects performance on the YBT-UQ in swimmers.

Design:

Cohort study.

Patients or Other Participants:

Forty-three male and 54 female National Collegiate Athletic Association Division I college swimmers were recruited preseason.

Main Outcome Measure(s):

We measured YBT-UQ performance for the left and right limbs in the medial, inferolateral, and superolateral directions. The maximum score for each direction was normalized to upper extremity length. The average of the greatest normalized reach scores in each reach direction was used to develop a composite score (average distance in 3 directions/limb length LL] × 100). To examine reach symmetry between sexes, the difference in centimeters between the left and right sides was calculated for each reach direction prior to normalization. Statistical analysis was conducted using an independent-samples t test (P < .05).

Results:

Average scores in the medial (women: 92.5 ± 7.4%LL, men: 100.0 ± 8.7%LL; P < .01) and inferolateral (women: 85.6 ± 10.3%LL, men: 89.8 ± 10.8%LL; P = .05) directions and composite score (women: 83.4 ± 8.3%LL, men: 88.3 ± 8.9%LL; P < .01) were higher in men than in women. No differences were observed for reach symmetry in any direction.

Conclusions:

Performance on several YBT-UQ indices was worse for female than male collegiate swimmers. These results may have implications for the use of preseason and return-to-sport testing in swimmers as a measurement of upper quarter function and symmetry.Key Words: Y-Balance test, core stability, shoulder function, injury risk

Key Points

• Female collegiate swimmers exhibited worse performance than their male counterparts on the upper quarter Y- balance test in the medial and inferolateral directions as well as in the average overall score.
• No sex differences existed for reach symmetry for any of the reach directions.
• The worse performance in women may be associated with shoulder and core stability limitations, which may explain the increased incidence of upper quarter injuries in female swimmers.

Upper quarter injuries are the most common injuries sustained by collegiate swimmers.^1,2 More specifically, female swimmers have an increased risk of upper quarter injuries of the shoulder and back/neck compared with their male counterparts.^1,2 Sallis et al³ found that female swimmers sustained 21.05 and 8.19 injuries/100 participant years, whereas male swimmers experienced 6.55 and 1.45 injuries/100 participant years for the shoulder and back/neck, respectively. These injuries are disabling, often contribute to decreased performance and missed practices and competitions, and may require surgery. A number of extrinsic and intrinsic variables have been shown to contribute to the increased risk of upper quarter injuries, regardless of sex.^2,4–11 Extrinsic factors include rigorous training exposure focusing on shoulder-intensive movements, reduced cross-training or participation in other sports, prior injury, and age. Intrinsic risk factors include laxity of the capsuloligamentous structures, decreased core and scapular muscle endurance, and scapulothoracic and glenohumeral muscular imbalance; screening tools to assess these components and eventually minimize the role these factors play in overall injury risk for swimmers may be helpful. Currently, insufficient data exist for upper quarter functional testing in swimmers. Additional upper quarter functional testing may further explain the possible sex-related characteristics associated with injury disparity. Effective and functional upper quarter testing could be used to help develop offseason and dry-land training programs focused on performance enhancement and injury prevention.^12,13Swimming requires a significant amount of upper body and core strength, endurance,^11,14 and shoulder mobility and stability.⁵ Although a number of tests have been designed to assess upper quarter function, few tests assess upper quarter stability at the limit of closed chain stability,^15–18 which has been associated with performance enhancement and injury prevention in swimmers.^12,13 The upper quarter Y balance test (YBT-UQ) can be conducted in the field setting with minimal equipment and examines the unilateral performance of the upper quarter at the end range of the athlete''s ability to maintain stability.^15–18 The YBT-UQ challenges the core and upper quarter strength, stability, and mobility that are required for the performance demands of swimming.^13,16,18 The YBT-UQ is a reliable functional test,^16,18 demonstrating a fair to moderate association with several tests that measure core stability (push-up and lateral side bend endurance, range, 0.38–0.45) and upper extremity function (closed kinetic chain upper extremity stability test, range, 0.43–0.49).¹⁸ Current research supports the notion that YBT-UQ performance is not affected by competition level,¹⁹ sex, or limb dominance in active adults¹⁸ and healthy college students.¹⁶ However, performance on the YBT-UQ has yet to be assessed in swimmers, who have different upper quarter demands than previously tested populations.Previous authors³ have shown that female swimmers are at increased risk for injury to the upper quarter compared with their male counterparts. Reasons for this discrepancy are unknown. Basic tests of upper extremity function in athletes, particularly those in sports with significant upper quarter demands, may allow us to identify movement limitations that can be addressed to improve the athlete''s endurance. Such tests may also be beneficial in assessing progress in dry-land training programs aimed at improving swimming performance.¹³ Given the current gaps in the literature, it is beneficial to examine YBT-UQ performance in male and female swimmers to determine if sex differences exist in performance. Based on previous research, we expected no sex difference on the YBT-UQ.^16,18