Sports Medicine Research: In the Lab & In the Field: Scapular Strength Increased with Training but not Endurance in Adolescent Swimmers (Sports Med Res)


Friday, March 25, 2011

Scapular Strength Increased with Training but not Endurance in Adolescent Swimmers

Scapular-Muscle Performance: Two Training Programs in Adolescent Swimmers

Van de Velde A, De Mey K, Maenhout A, Calders P, Cools AM. J Athl Train. 2011 Mar-Apr; 46(2):160-7.

Scapular dyskinesis is a term that has gained popularity in the past 20 years. It describes an alteration in the motion of the scapula during overhead movements. Dr. Ben Kibler has been on the forefront of identifying that alterations in scapular kinematics and muscular activation occur in overhead athletes and may contribute to the development of shoulder injuries. Since the scapula only has an indirect bony attachment to the thorax, it relies heavily on dynamic stability. Several neuromuscular imbalances have been identified in overhead athletes including an over active upper trapezius and lower trapezius inhibition. The serratus anterior has also been described as having a fatigue-related inhibition. This is detrimental to the shoulder complex due to these muscles being involved in the scapular upward rotation force couple. Recently, research has been geared at examining exercise protocols to determine the most effective strategy to maintain scapular strength and endurance. This study used 18 adolescent swimmers and divided them into a strengthening group and an endurance group. A total of 6 bilateral exercises were used over a 12 week period and the only difference between groups was the number of repetitions (strength group 3 sets of 10 and the endurance group 3 sets of 20). The subjects were tested on an isokinetic dynamometer at 2 speeds (60°/sec and 180°/sec) for scapular protraction and retraction. From that testing several variables were calculated including peak force, protraction/retraction peak force ratio, and fatigue index (a ratio of the difference in output during the first and third portions of the test). They found that swimmers had side-to-side difference for scapular retraction both before and after training. After training both protraction and retraction strength improved on the non-dominant arm. The fatigue indexes for protraction on both sides and retraction on the non-dominant side were higher after the training regardless of group. There were no differences between training groups for peak force or fatigue index.

This study has several interesting findings that are very clinically relevant. Examining this in adolescents is crucial to reduce injury risk at a young age. It also helps to identify scapular strength and endurance differences that exist in this population due to swimming. Although swimming is a bilateral sport there were still side-to-side differences in scapular retraction strength. Commonly swimmers have a favored breathing side, which is more commonly injured, however this study used swimmers that breathe equally on both sides. Scapular retraction is a very important motion that requires adequate strength and endurance. Kilber describes the full scapular retraction position as the full tank of energy. Suggesting that the energy produced by the lower extremity and the core can be transfer to the shoulder if the scapula is in full retraction. Any decreases in strength or endurance will create a break in the kinetic chain and loss of energy. This data suggests that swimmers must focus on strengthening both arms to help offset some asymmetries in strength. It is interesting that regardless of which group subjects were in both improved in strength but not endurance. This may be due to the number of repetitions (endurance group only 10 more than strength) or that swimmers already have superior scapular endurance and should focus on strength and neuromuscular control. It would be interesting to examine the swimmers neuromuscular control to see even though they improved strength and had optimal endurance was the scapula muscles firing in a normal pattern and producing smooth fluid motion. What are your experiences with scapular strengthening or endurance exercises? Do you see improvements? Do you do these exercise preventively or just after injury? Let us know so we can begin to create a more efficient program for athletes.

Written by: Stephen Thomas

Reviewed by: Jeffrey Driban


Tom Martin said...

When performing scapular rehab I usually focus on strength over endurance. With swimmers specifically I usually have a tight posterior capsular component also.

But it would be interesting to devise a program with high reps and controlled rest b/w sets/exercises.
Or utilize core stab ex between sets to increase total work t/o the program.

Interesting topic.

Stephen J. Thomas, PhD, ATC said...

Tom thanks for the comment. Here is a loaded question for you. Do you think the tight posterior capsule plays a role in the strength and neuromuscular control of the scapula? So if we improve posterior capsule mobility we will allow the scapular muscles to fire correctly and increase strength?

Tom Martin said...

Great question.
What comes first????

Personally I like to correct the capsular tightness and give stage I type scapular exercises (working scapula bilaterally with arms at side and 90 degrees, elev/dep, pro/retx)

Focus on capsule but address scapular muscle as GIRD decreases.

The swimmers I have treated (HS level) that I catch early in their symtomalogy seem to do well as their GIRD decreases.

So I would be on the side of the correcting the capsular flexibility to allow the scap muscle to work properly.

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