Effects of bench press technique variations on musculoskeletal shoulder loads and potential injury risk

Abstract

While shoulder injuries resulting from the bench press exercise are commonly reported, no biomechanical evidence for lowering injury risk is currently available. Therefore, the aim of the present study was to compare musculoskeletal shoulder loads and potential injury risk during several bench press variations. Ten experienced strength athletes performed 21 technical variations of the barbell bench press, including variations in grip width of 1,1.5 and 2 bi-acromial widths (BAW), shoulder abduction angles of 45°, 70° and 90°, and scapula poses including neutral, retracted, and released conditions. Motions and forces were recorded by an opto-electronic measurement system and an instrumented barbell. An OpenSim musculoskeletal shoulder model was employed to estimate joint reaction forces in the glenohumeral and acromioclavicular joints. Time-series of joint reaction forces were compared between techniques by statistical non-parametric mapping. Results showed that narrower grip widths of $<1.5$ BAW decreased acromioclavicular compression (p < 0.05), which may decrease the risk for distal clavicular osteolysis. Moreover, scapula retraction, as well as a grip width of $<1.5$ BAW (p < 0.05), decreased glenohumeral posterior shear force components and rotator cuff activity and may decrease the risk for glenohumeral instability and rotator cuff injuries. Furthermore, results showed that mediolaterally exerted barbell force components varied considerably between athletes and largely affected shoulder reaction forces. It can be concluded that the grip width, scapula pose and mediolateral exerted barbell forces during the bench press influence musculoskeletal shoulder loads and the potential injury risk. Results of this study can contribute to safer bench press training guidelines.

Keywords: bench press; biomechanics; glenohumeral joint; injury prevention; musculoskeletal model; rotator cuff; shoulder; strength training.

FIGURE 1

Pictures of the experimental setup. (A) shows the purple tape that was placed on the barbell to indicate the grip width and shows an example shoulder abduction angle of 45°. (B) shows the orange cones placed beneath participants’ elbows at the desired shoulder abduction angle to monitor if the correct angles were maintained during the bench press. In addition, this picture shows the swimming pool noodle that was placed beneath the spine of the athlete, to release the scapulae from the bench. It must be noted that the participant only lifted his head in (B) to show the swimming pool noodle. During the actual measurements, the head was always in contact with the bench.

FIGURE 2

Musculoskeletal model with (A) scapular degrees-of-freedom and (B) shoulder muscles that control the scapula. Reprinted from Seth et al. (2019).

FIGURE 3

Glenohumeral stability constraint. If the glenohumeral joint reaction force (JRF_GH) threatens to point outside of the glenoid fossa, indicated by θ exceeding θ _max, the humeral head stabilizers will typically be activated to ensure that the reaction force remains directed within the glenoid fossa. Reprinted from Belli et al. (2023).

FIGURE 4

Effects of grip width on the (A) total glenohumeral reaction force, (B) glenohumeral compression force, (C) glenohumeral anterior shear force component, (D) glenohumeral superior shear force component, (E) total acromioclavicular reaction force, (F) acromioclavicular compression force, (G) acromioclavicular anterior shear force component, and (H) acromioclavicular superior shear force component. Top subplots show the mean and between-subject variation (shaded) in forces for grip widths 1 (blue), 1.5 (black) and 2 (red) times the bi-acromial-width during a bench press cycle with a total barbell mass of 16 kg. The middle and bottom subplots represent the results from statistical non-parametric mapping (SnPM) indicating if and when during the bench press cycle there is a significant difference (grey) on the outcome parameter between grip widths.

FIGURE 5

Effects of scapula pose on the (A) total glenohumeral reaction force, (B) glenohumeral compression force, (C) glenohumeral anterior shear force component, (D) glenohumeral superior shear force component, (E) total acromioclavicular reaction force, (F) acromioclavicular compression force, (G) acromioclavicular anterior shear force component, and (H) acromioclavicular superior shear force component. Top subplots show the mean and between-subject variation (shaded) in forces for the scapula poses Neutral (blue), Retracted (black) and Released (red) during a bench press cycle with a total barbell mass of 16 kg. The middle and bottom subplots represent the results from statistical non-parametric mapping (SnPM) which shows if and when during the bench press cycle there is a significant difference (grey) on the outcome parameter between scapula poses.

FIGURE 6

Effects of shoulder abduction angle on the (A) total glenohumeral reaction force, (B) glenohumeral compression force, (C) glenohumeral anterior shear force component, (D) glenohumeral superior shear force component, (E) total acromioclavicular reaction force, (F) acromioclavicular compression force, (G) acromioclavicular anterior shear force component, and (H) acromioclavicular superior shear force component. Top subplots show the mean and between-subject variation (shaded) in forces for the shoulder abduction angles 45 (blue), 70 (black) and 90 (red) degrees during a bench press cycle with a total barbell mass of 16 kg. The middle and bottom subplots represent the results from statistical non-parametric mapping (SnPM) which shows if and when during the bench press cycle there is a significant difference (grey) on the outcome parameter between shoulder abduction angles.

FIGURE 7

Effect of (A) grip width, (B) scapula pose, and (C) shoulder abduction angle on Supraspinatus Anterior activity. Subplots show the mean and between-subject variation (shaded) in activities for the different technique conditions (blue, red, black) during a bench press cycle with a total barbell mass of 16 kg. Muscle activities are expressed relative to a maximum activity of 1.