Activation of Shoulder Musculature During Upper Extremity Weight Bearing Exercises

Research Review: Activation of Shoulder Musculature During Upper Extremity Weight Bearing Exercises

By Jinny McGivern PT, DPT, Certified Yoga Instructor

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Uhl, T. L., Carver, T. J., Mattacola, C. G., Mair, S. D., & Nitz, A. J. (2003). Shoulder musculature activation during upper extremity weight-bearing exercise. Journal of Orthopaedic & Sports Physical Therapy, 33(3), 109-117. ARTICLE

Why is this relevant?:

The push-up is a commonly studied closed kinetic chain (CKC) exercise for the upper extremity (UE). It has been hypothesized that CKC activities promote joint stability and an increased level of co-contraction of muscles surrounding joints. The push up is a fairly demanding exercise and may not be appropriate for all populations. This research provides information about a spectrum of CKC exercises for the UE to allow for informed decisions regarding progression of these types of activities.

Caption: Dr. Brent Brookbush instructs personal trainer, Mike Tierney on correct form for a traditional push-up.

Standard Push Up (Dynamic Plank)

Study Summary

Caption: Dr. Brookbush instructs Melissa Ruiz on how to regress a stability ball push-up.

Stability Ball Push-up

Review & Commentary:

The authors of this study examined the activation levels of 5 muscles that cross the glenohumeral joint over the following spectrum of closed kinetic chain (CKC) exercises: Prayer pose (otherwise known as child's pose or prone heel sit), Quadruped (shoulder flexion and hip flexion to 90 degrees), Tripod (quadruped with non dominant UE raised to 180 degrees), Pointer (Tripod with contralateral lower extremity extended to 0 degrees extension), Push up (holding a plank position with elbows straight), Push up with feet elevated (45cm) and One arm push up (non dominant hand placed behind back.)

There were many strengths to the methodology of this study. The authors used excellent standardization procedures including: an orientation session for the subjects to familiarize themselves with the exercises; standardized placement of each scale to measure load (via measurements across clavicle); standardized and previously validated methods of electrode placement for EMG recording; as well as a goniometer used to standardize 90 degrees of shoulder flexion for quadruped and push up positions. The authors clearly acknowledge the limitations of surface EMG and reported the precautions they took to minimize cross talk from other muscles (placement of electrodes near mid section of each muscle with respect to standardized anatomical landmarks, small electrodes, small sampling area). All EMG data was normalized to Maximal Voluntary Contractions (MVICs) for each muscle so that the differences in electrical activity observed could be compared to a standard of muscle activity. All data on loading through the UE was normalized to each individuals body weight. The exercises were performed in a random order to prevent confounding results due to order bias.

There were also limitations to this research. The authors did not specify whether the gender of the subjects was male, female or of mixed population. There was no screening (i.e. range or motion, manual muscle test or other functional test) performed to assess function of the UE in the subjects, other than a history of injury and a determination that they could hold each position for 15s. It would have been helpful to have a more comprehensive picture of the subject's shoulder function to make it possible to infer appropriate exercise selection in those exhibiting movement impairments. The authors indicate that all subjects were healthy; therefore, it may not be safe to assume that the results of this study would also be observed in individuals with a pathology of the shoulder or UE. The exercises the researchers examined were static (isometric) positions; further research is needed to understand the activity of the UE in weight bearing dynamic activities. Finally, the authors chose to assess only muscles that acted on the glenohumeral joint. Future research should include information on other stabilizers of the shoulder girdle complex such as the serratus anterior , trapezius and rhomboids to allow for better understanding of the integrated function of the scapula and shoulder during CKC movement patterns.

Why is this study important?

This research confirms increased loading of the UE in CKC results in higher levels of muscle activation. Furthermore it provides nuanced information about the distribution of muscle activity throughout these positions.

How does it affect practice?

A comparison of different CKC exercises for the UE provides us with a greater understanding of how to sequence activities within a program to provide optimal challenges for a given patient or client at a given point in their rehabilitation or training. It supports the work of previous researchers that recommend use of weight bearing activities to strengthen the rotator cuff. It highlights that in a weight bearing position of 90 degrees of shoulder flexion, the infraspinatus demonstrates significantly higher levels of activity than the supraspinatus . This allows a greater level of specificity when designing exercise programs, and has implications for rehabilitation programs of tears or repairs to these muscles, as well as for postural dysfunction. In the early stages of a program, it may be desirable to limit the levels of activity of certain muscles in order to allow healing to occur, whereas later in a program it may be more appropriate to impose a greater challenge to a given muscle to increase strength. Finally, the authors provide insight into the differences between single arm CKC exercises versus double arm activities, and how different muscles are challenged as significant portion of the base of support is removed (the posterior deltoid is much more active in single arm UE CKC activities).

How does it relate to Brookbush Institute Content?

This research has applications to the management of postural dysfunction of the Upper Body (UBD) as described by the Brookbush Institute. The Brookbush Institute makes use of UE CKC exercises in multiple sections of a corrective exercise routine. This research has highlighted that the infraspinatus is one of the muscles with the highest levels of activation during these types of activities, while the activity of the supraspinatus is relatively minimized. This is a very positive and useful finding because in UBD , the infraspinatus has a propensity to become under-active, therefore in need of activation activities, while the supraspinatus has a tendency to become overactive, thereby benefiting from inhibitory activities. This research also reports that single arm activities tend to activate the posterior deltoid to a greater degree than double arm CKC exercises. This is good to keep in mind if your patient or client demonstrates a propensity towards over-activity of the posterior deltoid (the overactive synergist to the infraspinatus/teres minor complex). This research demonstrates that during a single arm push up activity (static hold on 1 UE) the infraspinatus activates to 86% MVIC and the posterior deltoid activates to 74% MVIC. During a bilateral push up position hold, the infraspinatus activates to 44% MVIC and the posterior deltoid activates to 18% MVIC. Infraspinatus activity is always greater, however during the single arm activity the posterior deltoid activity comes very close to matching. To maximize the effectiveness of infraspinatus training, it may be more beneficial to focus on double arm CKC activities first, then progress to single arm activities in subsequent sessions.

The first video below demonstrates techniques for strength testing the external rotators and highlights some of the compensations that one might see in individuals with overactive posterior deltoids and an under-active infraspinatus/teres minor . The next 2 videos are isolated activation and progression videos for the shoulder external rotators. The last 3 videos demonstrate CKC activity.

Shoulder External Rotator Manual Muscle Testing (MMT) for an Active Population

External Rotator Isolated Activation

External Rotator Activation Progression

Quadruped

Plank

Push-up

© 2016 Brent Brookbush

Questions, comments, and criticisms are welcomed and encouraged -