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The Athletic Shoulder (ASH) test: reliability of a novel upper body isometric strength test in elite rugby players

Ashworth, B., Hogben, P., Singh, N., Tulloch, L. and Cohen, D.D., 2018. The Athletic Shoulder (ASH) test: reliability of a novel upper body isometric strength test in elite rugby players. BMJ Open Sport & Exercise Medicine, 4(1), p.e000365.

In today’s letter

• Overview of the study looking at the athletic shoulder test reliability and effectiveness at determining return to sport readiness

• Rapid Results = Its a reliable and useful objective measure to use when considering returning athletes to sport

• Professional takeaway = Include the test to give you insights on the shoulders ability to produce force at long lever (compromised) positions

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Definitions

1. ASH TEST: The ASH (Athletic shoulder) test is a clinical assessment using force plates or handheld dynonometer to measure peak force development (strength), commonly used to measure outcomes in athletes aiming to return to sport

2. Inter-day Reliability: Inter-day reliability assesses the consistency and stability of measurements taken on different days, providing insight into the degree to which a test or measurement tool produces consistent results over multiple testing sessions.

3. Absolute Reliability: Absolute reliability refers to the extent of consistency in measurements, irrespective of changes in the participants being measured.

   *A low inter-day measurement error is considered desirable, and values below 5% are often considered good. Keep in mind that what is considered acceptable may depend on the field of study*

Aim of study

• Investigating the reliability of a newly developed set of long lever upper body isometric force platform tests

  

Background info

• Players face heightened injury risks during tackling, defensive drills, and high-speed situations, especially in long lever arm tackles, due to increased collision forces and unstable positions.

• Shoulder injuries tend to occur later in training and matches, with fatigue contributing to the heightened risk from repeated tackling exposure.

• Elite sports commonly use lower limb isometric tests to monitor force reductions as indicators of potential fatigue.

• Isometric tests on recovery days post-match offer a potentially safer alternative to eccentric tests, minimising the risk of muscle damage.

• In sports like rugby or overhead sports prone to shoulder injuries, there is a lack of assessment tools, making a long lever isometric test valuable for evaluating athlete capabilities and reducing injury risks.

• Isokinetic dynamometry is a gold standard for strength assessment, but its systematic implementation is challenging in sports and clinical settings.

• Hand-held dynamometry is a quicker, portable, and more cost-effective method for evaluating shoulder strength in team sports environments.

• The reliability of Hand-held dynamometry is questioned due to varying test protocols, warm-up strategies, tester and subject positions, shoulder positions, tester strength, subject stabilisation, and equipment stabilisation.

• Hand-held dynamometers stability during a test is influenced by the relative strengths of the tester and subject, with reliability compromised if the subject exceeds 30 kg of force production.

• An alternative to Hand-held dynamometry is assessing isometric force using a force platform, a gold standard tool, eliminating operator strength as a potential source of error.

• A long lever isometric test is proposed as a suitable method to replicate shoulder muscle contraction in the tackle position.

• Such a test could serve as a valuable tool for assessing athlete capabilities and reducing injury risks in sports with common shoulder injuries.

• The study aims to establish the reliability and clinimetrics of this novel long lever upper body isometric force platform test.

 Methods

• The study involved the participation of 18 male rugby players at the elite level.

• Exclusion criteria encompassed players with recent acute neck or shoulder girdle injuries (<72 hours before testing), those experiencing symptoms persisting beyond 20 minutes post-test, worsened pain linked to testing, or those unable to assume test positions due to limited range of motion.

• The inclusion criteria aimed to ensure participants were free from recent injuries, adverse post-test effects, or restrictions in range of motion for accurate study results.

Performing the ASH test

• All assessments were conducted with the participant lying prone on the floor, ensuring standardised neck positioning using a 4 cm foam block supporting the forehead.

• The hand was strategically positioned on a vertical axis force platform.

• In the I-test, the shoulder was fully abducted (aligned with the body), the forearm in pronation, and the force platform engaged with the heel of the hand.

• For the Y-test and T-test, the arm was set at 135° and 90° shoulder abduction, respectively, maintaining full elbow extension in all cases.

• A thorough warm-up involved two sub-maximal efforts at 80%–90% intensity for each testing position.

• Players underwent three trials in each of the three positions on one limb, followed by a repetition on the contralateral limb.

• Optimal recovery was achieved with a 20-second rest period between efforts.

• The contralateral arm was positioned behind the back, restricting elbow fixation and providing anti-rotation trunk stability for the Y and T tests. However, in the I-test, the arm could remain by the subject’s side due to lower trunk rotational forces encountered.

• Trunk stabilisation against rotation without the use of the contralateral arm was crucial, with the subject exerting downward force from the shoulder through the heel of the hand.

• Each effort commenced with a countdown, prompting subjects to push forcefully and rapidly to generate maximal force, sustaining it for the entire 3-second test duration.

• Test exclusions occurred if countermovement was detected (hand lifting before pushing down), or if compensatory strategies were observed, such as excessive lower limb use for stability, anterior scapular tilt, or elbow flexion.

Results

• The consistency of measurements taken on different days, known as "interday reliability," was found to be excellent. This was measured using a statistic called "Intraclass Correlation Coefficients," which helps assess how much the measurements agree across different testing days.

• The study also indicated that the reliability of the measurements was high, as reflected in the "absolute reliability values." These values, represented by the Standard Error of Measurement (SEM), ranged from 4.8 to 10.8.

• The "interday measurement error," or the degree of variation in measurements from day to day, was consistently below 10% across all test positions.

Discussion

• A series of innovative isometric long lever shoulder tests conducted on a force platform displayed exceptional reliability (ICCs 0.94–0.98) across the three 'IYT' positions.

• Practitioners can rely on the force platform IYT tests to consistently detect both between-subject and within-subject differences.

• While high reliability is crucial, it does not inherently guarantee a test's sensitivity to identify genuine changes.

• A meaningful change in the dominant arm T-test is considered to be >13.3 N, with a 90% confidence level.

• The interpretive power of the ASH test aligns comparably with relevant isometric tests found in the literature.

• Beyond reliability and interpretability, a new test should also demonstrate validity and a clear purpose.

• The force platform, a gold standard for force measurement, is valid for assessing isometric strength.

• The T-position mirrors the 'arm tackle' stance, while the I-position closely replicates the injury mechanism seen in 'try-scorer' scenarios.

• Both tests involve a straight arm with force applied at the end of a long lever, reflecting the higher torques and force transfer demands encountered in sporting actions compared to the majority of short lever (bent arm) tests in existing literature.

• The ASH test may prove valuable in tackling sports and other activities that expose the shoulder to longer lever stress or demand the ability to transfer forces across the shoulder girdle.

Clinical implications

• Return to sport: Use this test to aid a safe return to arm tackling/swimming/serving etc. during the return-to-play process.

• Quantifying Muscle Recovery: The test can be served as a tool to measure muscle function recovery post-exercise or training/match exposure, comparing results to a player's baseline values.

• Comprehensive Shoulder Evaluation: It’s recommended incorporating the test into a cluster of assessments, including strength, range of motion, and control, for a comprehensive understanding of shoulder stability maintenance

• Side-by-Side Comparison: Utilise the test to identify disparities between sides, with an established gold standard of 6%-9% difference for an ideal return to sport.

• Gradual Exercise Advancement: Progress through exercise positions, starting with isometric push into a wall using a Swiss ball, advancing to eccentric single-arm push-up sliders, and concluding with TRX push-outs. (athlete discomfort depended)

Limitations

• Minor variations in reliability exist among the three test positions, potentially attributed to differing requirements for subjects to stabilise their trunk against rotational forces.

• Comparisons of reliability between test positions are not feasible without randomising the test order for each subject, as our study design does not facilitate this comparison.

• While a standing test might be more sports-specific for assessing force production in a standing tackle, the prone position on the floor, despite being less sports-specific, offers higher reliability by minimising involvement of other body segments and reducing test-retest variability.