Electromyographic analysis of selected shoulder muscles during a series of exercises commonly used in patients with symptomatic degenerative rotator cuff tears

Key points

1. 01Anterior deltoid activity rose stepwise from about 6% to 40% of maximum across the bench and wall slide progression, and up to 33% in the hardest Levy exercise.
2. 02Infraspinatus (a cuff muscle) stayed low throughout, never exceeding 15.86% of maximum, supporting the idea these are low-cuff-load exercises.
3. 03Adding elastic-band resistance to wall slides was the main way to drive up deltoid and scapular activity.
4. 04For the Levy exercises, tilting the trunk forward 45 degrees was what increased activity in all measured muscles.
5. 05Older participants (47 to 60 years) showed higher anterior deltoid, infraspinatus, and middle trapezius activity and lower lower-trapezius activity during the slides.

How it was conducted

Design

Basic science kinesiology study; surface EMG of 8 shoulder muscles during 13 exercises

Participants

55 healthy adults (30 men, 25 women), aged 18 to 60 years, no shoulder or neck injury, surgery, or heavy overhead training

Age groups

18 to 32 years (N=22), 33 to 46 years (N=10), 47 to 60 years (N=23)

Exercises

8 bench and wall slide variations plus open-chain elevation reference, and 4 Levy anterior deltoid progressions

Outcome

Mean EMG amplitude per muscle expressed as percent of maximal voluntary isometric contraction (% MVIC)

Analysis

Repeated-measures ANOVA per muscle with Bonferroni post-hoc; two-way ANOVA for exercise by age, alpha 0.05

What they found

• Anterior deltoid ranged from 6.08% MVIC (Ex 2) to 39.63% MVIC (Ex 8), with significant increases (p<0.05) across all progressions except Ex 1 to 2 and Ex 6 to 7.
• Infraspinatus never exceeded 15.86% MVIC across the bench and wall slide set.
• In the Levy set, anterior deltoid rose from 8.18% MVIC (Ex 10) to 32.70% MVIC (Ex 13), differing significantly among all 4 exercises; other muscles only increased significantly from Ex 12 to 13 (p<0.05).
• Significant exercise-by-age interactions during the slides for anterior deltoid (p=0.006), middle trapezius (p=0.009), lower trapezius (p<0.001), serratus anterior (p<0.001), and infraspinatus (p=0.01).
• Older group (G3) had higher anterior deltoid than youngest (G1) at Ex 3, 4, 5 (p=0.003, 0.001, 0.001) and higher infraspinatus at Ex 3 to 9 (p=0.020 to 0.007).
• Lower trapezius was higher in the youngest group at Ex 7, 8, 9 (p=0.039, 0.012, <0.001).
• No significant exercise-by-age interaction or main age effect for the Levy exercises.

Limitations

• Tested healthy volunteers, not patients with rotator cuff tears, who may recruit the deltoid differently.
• Older participants had no imaging, so some may have had unrecognized asymptomatic cuff tears.
• The middle age group was small (N=10), so the age subgroup analysis may be underpowered.
• Surface EMG of the infraspinatus can be affected by crosstalk from nearby muscles.

Why it matters

For patients

If you are managing a cuff tear without surgery, these exercises let your therapist gradually increase work for the deltoid and shoulder-blade muscles without heavily loading the torn tendon.

For clinicians

The data give a graded sequence (add band resistance to wall slides, add trunk inclination to Levy exercises) that raises deltoid and scapular activity while keeping infraspinatus below 20% MVIC, and flag age-related recruitment differences.

For readers

This is a laboratory muscle-activation study in healthy people, useful for designing exercise progressions but not evidence that the program improves patient outcomes.