It is not surprising that throwing athletes require significant shoulder strength. A throwing action demands humeral internal rotation velocity up to 7,500 degrees per second! Moreover, measuring shoulder strength holds relevance across various disciplines, including catching, diving, saving, and tackling, as well as athletes with shoulder injury history.
Different methodologies exist to assess shoulder strength. Isokinetic dynamometry, albeit comprehensive, faces accessibility challenges. Conversely, handheld dynamometers enhance portability but demand meticulous attention to precision and inter-tester reliability. The ASH shoulder test, a novel creation by Ben Ashworth, introduces a force plate-based assessment of shoulder strength, capturing rate of force development and force production across prone lying positions in the I Y and T shoulder configurations.
Measuring Internal and External Rotation Strength
Today, our focus lies on evaluating internal and external rotation shoulder strength using a fixed dynamometer, such as VALD's ForceFrame. For those interested in handheld dynamometry options, their DynaMo product enables an easily portable approach to strength testing through dynamometry.
The video below illustrates how to use the VALD Performance ForceFrame to measure shoulder strength through internal and external rotation, as well as discussing other options that are available to measure shoulder strength.
Internal (IR) and external (ER) rotation are movements of the shoulder joint that involve rotating the arm inward or outward. Internal rotation activates the muscles in the chest and front of the shoulder, while external rotation works the muscles in the back of the shoulder and upper back. During throwing, the shoulder can be in a potentially extreme range of external rotation in the cocking phase, before horizontally adducting and internally rotating, placing high eccentric stress on the shoulder external rotators (Burkhart et al., 2003).
Quantifying IR and ER strength can clearly be valuable to tracking capacities and imbalances. Testing this will the ForceFrame parallels the hip abduction and adduction testing methodology. Learn more about hip and groin testing in this blog post.
Internal rotation uses the force cells employed for groin squeezes, while external rotation engages the outer force cells that are also used for hip abduction. Ensuring precise alignment of the athlete's arms with the designated paddles on the ForceFrame is imperative for accurate testing outcomes. See the video above for illustrations of potential testing positions. Whatever positions you select, maintaining consistency and no movement (this is an isometric testing position) forms the foundation for a rigorous testing protocol.
This test will capture isometric force output in four dimensions: IR on the left, IR on the right, ER on the left, ER on the right (see figure below). Much like lower-body asymmetries, left-to-right differences can be assessed. However, it is likely there will naturally be differences in the capacity of each side, especially in throwing athletes, given the impact of different load demands on adaptation and capacity on each side.
The ER: IR Shoulder Ratio
Arguably of greater interest in shoulder testing however, is the external rotation to internal rotation (ER:IR) ratio.
The ER:IR assessing the within-shoulder balance (or imbalance). So the ER capacity vs IR capacity on each side. On the dominant throwing side, this can be particularly critical to track.
While asymmetry in throwing athletes is commonplace, monitoring fluctuations in the ER:IR ratio over time aids in identifying potential imbalances necessitating corrective interventions.
That said, we are not necessarily seeking a ratio of 1.0. Throwing demands a natural imbalance in the dominant arm, so ratios less than 1 can be common in throwers as well as swimmers (see video right). Establishing an athlete's normal range and tracking over the course of the season, plus in rehabilitation if injuries occurs, provides an objective approach to shoulder capacity monitoring.
Of course, internal and external rotation strength testing remains just one facet of a comprehensive testing regime, best complemented by assessments targeting other aspects of the kinetic chain. Grip strength assessments and hip and groin strength testing, among others, enhance our understanding of athlete performance and injury risk - particularly in throwing athletes - facilitating our ability to tailor individual interventions.
In conclusion, testing IR and ER with a fixed dynamometer, such as VALD's ForceFrame, offers a straightforward, non-fatiguing means of assessing shoulder strength. Establishing norms for each individual is critical given the different demands throwing athletes can be exposed to, both within and between shoulders. Tracking the ER:IR ratio in particular can be valuable.
Frequently Asked Questions (FAQs) on Measuring Shoulder Strength
How can shoulder strength be assessed?
Shoulder strength can be assessed through various methods, including manual muscle testing, isokinetic dynamometry, fixed frame dynamometry, force plate assessments like the ASH test, and functional movement assessments. Each method has its own advantages and challenges related to accessibility, portability, and accuracy.
How is internal and external rotation strength measured?
Internal and external rotation strength can be measured using a fixed dynamometer, such as VALD's ForceFrame. This method captures isometric force output at the wrist, most commonly in a supine position with the arm being assessed bent to 90 degrees shoulder abduction and elbow flexion.
What is the ER:IR ratio?
The ER:IR shoulder ratio evaluates the balance between external and internal rotation strength within each shoulder. Monitoring this ratio helps identify potential imbalances that could lead to injuries, especially in the dominant arm of throwing athletes. There is no fixed ideal ER:IR ratio, as natural imbalances are common in athletes depending on their sport's demands (e.g., throwing athletes, swimmers). Instead, it's important to establish an athlete's normal range and monitor changes over time to detect any significant deviations that might require intervention.
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This article is support by VALD Performance. For more information, about their technology, visit their website.