PART 2: Bench Press Width & Muscle Activation. 

Due to the length and the HUGE amount of research with regards to the different muscles below and their activation patterns, we have decided to post the link to all the studies below so that you can read it in your own time! ALL references are included in the link below. 

- PECTORALIS MAJOR
- DELTOIDS
- TRICEPS
- LATISSIMUS DORSI
- BICEPS BRACHII
- ERECTOR SPINAE
- ABDOMINALS

EMG STUDIES: http://www.strengthandconditioningresearch.com/…/bench-pr…/…

However, activation on the `rotator cuff` muscles will be discussed based on a study conducted by Wattanaprakornkul et al. (2011). The importance of the rotator cuff is often `forgotten` with regards to the bench press movement; which is clearly illustrated in the lack of images including the `rotator cuff` when you look at the `common anatomy of a bench press` in a image search! See image below for an example! 

DISCUSSION:
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The results of this study indicate that the commonly performed bench press and row exercises recruit RC muscles at levels similar to flexion and extension exercises performed in prone lying. There were no significant differences in the activity levels of the RC muscles between bench press and flexion exercises and between row and extension exercises.

The RC recruitment patterns during bench press and row exercises however, differed from that observed between flexion and extension exercises. During the flexion and extension exercises performed in prone all RC muscles examined exhibited a direction-specific recruitment pattern (Wattanaprakornkul et al., 2011a). In contrast, only the posterior RC (supraspinatus and infraspinatus) were recruited at significantly higher levels during the bench press compared with the row exercise, with no significant difference in anterior RC (subscapularis) activity levels between these two exercises. In addition, although there was no significant difference in posterior RC activity levels during either the bench press or row exercises with infraspinatus and supraspinatus recruited at similar levels, only part of the posterior RC (infraspinatus) exhibited a reciprocal recruitment pattern with subscapularis during the bench press and row exercises. Infraspinatus was recruited at significantly higher levels than subscapularis during the bench press, while subscapularis was recruited at significantly higher levels than infraspinatus during the row exercise. Subscapularis and supraspinatus activity levels were not significantly different in either bench press or row exercises.

These results indicate that RC muscles are recruited in a direction-specific pattern during bench press and row exercises similar to the RC recruitment pattern previously demonstrated during flexion and extension exercise performed in prone (Wattanaprakornkul et al., 2011a). Part of the posterior RC (infraspinatus) was recruited at significantly different levels to the anterior RC (subscapularis) during both the bench press and row exercises. This reciprocal recruitment pattern of some RC muscles indicates that RC co-activation at similar levels – in order to globally compress the articular surfaces – cannot be the mechanism whereby the RC muscles are providing shoulder joint dynamic stability during bench and row exercises. The significantly higher posterior RC activity during bench press (a flexion-like exercise) and significantly higher anterior RC activity during row (an extension-like exercise) supports the hypothesis proposed by Wattanaprakornkul et al. (2011a) that the RC provides shoulder joint support by preventing flexion and extension prime movers of the humerus from translating the humeral head on the glenoid fossa.

With respect to the muscles examined which are capable of producing extension or flexion torque (Palastanga et al., 2006 and Rockwood and Matsen, 2009), the results of this study indicate that activity levels were more similar between the row and extension exercises examined than between the bench press and flexion exercises. While latissimus dorsi and deltoid did not differ in their recruitment patterns between row and extension exercises, significant differences in activity levels in the muscles capable of producing flexion torque were found between the bench press and flexion exercises. Although there were no significant differences in pectoralis major and deltoid activation levels during the bench press exercise, pectoralis major was activated at significantly higher levels in the bench press exercise compared with flexion, while deltoid was activated at significantly higher levels during the flexion exercise compared with bench press. These differences are probably due to differences in the “flexion” tasks examined. The bench press exercise was performed from a starting position with the shoulder in 20–30° abduction while the flexion exercise was performed with the arm by the side of the body i.e. 0° abduction. Therefore, while both exercises involved movement into shoulder flexion, the bench press also involved shoulder adduction. Significantly higher recruitment of pectoralis major, which produces both shoulder flexion and adduction torque (Palastanga et al., 2006) would therefore, be expected during the bench press exercise compared with the flexion exercise.

The significantly different activity levels recorded in pectoralis major and latissimus dorsi during the bench press and row exercises examined, provide evidence to suggest that the RC muscles are functioning to stabilize the shoulder joint during these exercises in a similar manner to that proposed by Wattanaprakornkul et al. (2011) during flexion & extension exercises performed in prone (Wattanaprakornkul et al., 2011a). Higher pectoralis major activity was recorded during the bench press with higher latissimus dorsi activity during the row exercise. Evidence indicates that activity in pectoralis major can cause an anterior displacement of the humeral head (McMahon et al., 2002 and Sinha et al., 1999) which infers that activity in latissimus dorsi will result in posterior humeral head translation. Similar to the manner in which the inferior RC muscles prevent deltoid from superiorly translating the humeral head during shoulder abduction (Blasier et al., 1992, Inman et al., 1944 and Sharkey et al., 1994), RC muscles are recruited during bench press and row exercises to prevent antero-posterior displacement of the humeral head. Infraspinatus (a posterior RC muscle) was recruited at significantly higher levels than subscapularis (anterior RC muscle) during bench press to counterbalance the potentially destabilizing anterior translational forces produced by pectoralis major. Similarly, subscapularis was recruited at significantly higher levels than infraspinatus during the row exercise to counteract unwanted posterior humeral head translation due to latissimus dorsi activity.

The results of the current study have implications for RC rehabilitation programs. Since bench press and row exercises recruit the RC muscles in their role as stabilizers of the shoulder joint, these exercises offer a more functionally specific method of retraining the stabilizer function of these muscles than more commonly used rotation exercises which recruit the RC muscles in their torque producing role (Boettcher et al., 2010 and Dark et al., 2007). In addition, as bench press and row exercises recruit different RC muscles, they can be used to target particular RC muscles. Similar to external and internal shoulder rotation exercises, bench press and row exercises can specifically recruit infraspinatus and subscapularis, respectively. In contrast to rotation exercises, however, bench press and row exercises will not only specifically strengthen these RC muscles but also train the co-ordination necessary to enable them to respond to the potentially destabilizing forces generated by flexion and extension torque producing muscles.

As has been implied in a previous EMG study (Illyes and Kiss, 2005), deltoid was recruited at similar levels during the bench press and row exercises examined in the current study. Since both the bench press and row exercises were performed in similar degrees of shoulder abduction, similar levels of deltoid activity would be expected in order to maintain this abduction position. In addition, the main torque producing muscles in both the bench press (pectoralis major) and row (latissimus dorsi) exercises produce adduction torque (Palastanga et al., 2006 and Rockwood and Matsen, 2009). Deltoid activity would therefore, be necessary to prevent these muscles from adducting the shoulder i.e. deltoid is required to act as a synergist to prevent the unwanted adduction that these torque producing muscles would otherwise produce. Finally, anterior and posterior deltoid could have been contributing to producing shoulder flexion torque during bench press, and shoulder extension torque during row, respectively. It is possible that some activity from these parts of deltoid could have been recorded by the surface electrode placed over the middle of the belly of deltoid.

The activity levels recorded in upper and lower trapezius in the exercises examined in this study are mostly explained by the amount of scapular upward (lateral) rotation required to perform each exercise. Scapular upward rotation accompanies shoulder flexion and abduction in order to maintain shoulder joint articular surface contact as well as optimal alignment of the RC muscles, and upper and lower trapezius are the main components of the scapular upward rotation force couple as full range flexion/abduction is approached (Bagg and Forrest, 1986). The bench press exercise required movement to a maximum of 50% flexion range while the flexion exercise performed in prone required movement into full range flexion necessitating increased scapular upward rotation and the higher activity levels recorded in upper and lower trapezius. As both the bench press and row exercises were performed at approximately the same shoulder abduction position, the similar levels of upper and lower trapezius activity recorded during these exercises were to be expected.

Scapular upward rotation requirements, however, cannot explain the higher activity levels recorded in lower trapezius during the row compared to the extension exercise, and the higher serratus anterior levels recorded during the bench press exercise compared to the row exercise. We can only hypothesise that lower trapezius may have been providing some scapular retraction force (Boettcher et al., 2010), and serratus anterior some scapular protraction force, to “assist” in performing the row and bench press exercises, respectively.

Similar to other studies investigating muscle recruitment, as load increases during various shoulder tasks (Alpert et al., 2000, Boettcher et al., 2010, Dark et al., 2007, Reed et al., 2010, Wattanaprakornkul et al., 2011 and Wattanaprakornkul et al., 2011), the strategy to accommodate increasing bench press and row load is to establish the shoulder muscle recruitment pattern at low load and increase activity in all muscles as load increases. In both the bench and row exercise each muscle activated ⩾10% MVC had similar patterns of activity at low, medium and high load (r ⩾ 0.63, p < 0.05).

CONCLUSION (SHORT):
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Infraspinatus activity was significantly higher than subscapularis during bench press, with the converse pattern during the row exercise. Significant differences in activity levels were found in pectoralis major, deltoid and trapezius between the bench press and flexion exercises and in lower trapezius between the row and extension exercises. During bench press and row exercises, the recruitment pattern in each active muscle did not vary with load. During bench press and row exercises, RC muscles contract in a reciprocal direction-specific manner in their role as shoulder joint dynamic stabilizers to counterbalance antero-posterior translation forces.

REFERENCES:
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Alpert, S., Pink, M., Jobe, F., McMahon, P. and Mathiyakom, W. (2000). Electromyographic analysis of deltoid and rotator cuff function under varying loads and speeds. Journal of Shoulder and Elbow Surgery, 9(1), pp.47-58.

Bagg, S. and Forrest, W. (1986). Electromyographic study of the scapular rotators during arm abduction in the scapular plane. Available at: http://www.ncbi.nlm.nih.gov/pubmed/3717317

Blasier, R., Guldberg, R. and Rothman, E. (1992). Anterior shoulder stability: contributions of the rotator cuff forces and the capsular ligaments in a cadaver model. Journal of Shoulder and Elbow Surgery, 1 (3), pp. 140–150

Boettcher, C., Ginn, K. and Cathers, I. (2008). Standard maximum isometric voluntary contraction tests for normalizing shoulder muscle EMG. Journal of Orthopaedic Research, 26(12), pp.1591-1597.

Dark, A., Ginn, K. and Halaki, M. (2007). Shoulder Muscle Recruitment Patterns During Commonly Used Rotator Cuff Exercises: An Electromyographic Study. Physical Therapy, 87(8), pp.1039-1046.

Illyés, Á. and Kiss, R. (2005). Shoulder muscle activity during pushing, pulling, elevation and overhead throw. Journal of Electromyography and Kinesiology, 15(3), pp.282-289.

Inman, V., Saunders, J. and Abbott, L. (1944). Observations on the function of the shoulder joint. Journal of Bone and Joint Surgery, 26 (1), pp. 1–31

McMahon, P.J., Eberly, V.C., Yang, B.Y. and Lee, T.Q. (2002)
Effects of anteroinferior capsulolabral incision and resection on glenohumeral joint reaction force. Journal of Rehabilitation Research and Development, 39 (4) pp. 535–542.

Palastanga, N. and Soames, R. (2012). Anatomy and human movement. Edinburgh: Churchill Livingstone.

Reed, D., Halaki, M. and Ginn, K. (2010). The rotator cuff muscles are activated at low levels during shoulder adduction: an experimental study. Journal of Physiotherapy, 56(4), pp.259-264.

Rockwood, C. and Matsen, F. (2009). The Shoulder. Saunders/Elsevier, Philadelphia, PA.

Sharkey, N., Marder, R. and Hansen, P. (1994). The entire rotator cuff contributes to elevation of the arm. Journal of Orthopaedic Research, 12, pp. 699–708

Sinha, A., Higginson, D. and Vickers, A. (1999). Use of botulinum A toxin in irreducible shoulder dislocation caused by spasm of pectoralis major. Journal of Shoulder and Elbow Surgery, 8, pp. 75–76.

Wattanaprakornkul, D., Halaki, M., Boettcher, C., Cathers, I. and Ginn, K. (2011). A comprehensive analysis of muscle recruitment patterns during shoulder flexion: An electromyographic study. Clin. Anat., 24(5), pp.619-626.

Wattanaprakornkul, D., Halaki, M., Cathers, I. and Ginn, K. (2011). Direction-specific recruitment of rotator cuff muscles during bench press and row. Journal of Electromyography and Kinesiology, 21(6), pp.1041-1049.