Electromyographic comparison of infraspinatus, anterior, and posterior deltoid fibres during belly press exercise and triceps overactivity

Background/objective

The Belly Press Exercise (BPE) is a key clinical tool, but its efficacy is dependent on proper execution. This study aimed to clarify the muscle activation patterns that differentiate a proper BPE from an inappropriate pattern characterized by compensatory shoulder extension. We hypothesized that an appropriate pattern would involve greater posterior deltoid activation for stabilization, while the inappropriate pattern would show increased triceps brachii activity.

Methods

Surface electromyography was used to record the activity of the infraspinatus, anterior deltoid, posterior deltoid, and long head of the triceps brachii in 15 healthy male participants. The sample size was based on prior similar investigations (e.g., [13, 19]). Muscle activation was compared between two conditions: an appropriate pattern (isolated internal rotation) and an inappropriate pattern (internal rotation with 10° of shoulder extension) under three different load conditions (2, 5, and 10 % of body weight).

Results

Posterior deltoid activity was significantly higher in the appropriate pattern across all load conditions. In contrast, triceps brachii activity was significantly higher in the inappropriate pattern, particularly under the 5 % and 10 % load conditions. No significant differences were observed for the anterior deltoid or infraspinatus between patterns.

Conclusion

The posterior deltoid acts as a key stabilizer during a proper BPE, while overactivity of the long head of the triceps brachii is a clear indicator of compensatory shoulder extension. These findings provide clinicians with evidence-based markers for monitoring BPE form to ensure its therapeutic efficacy and safety.