Great Offset Loading Influences Core and Bench Press Peak Prime Mover's Activity in Trained Athletes

Area of Science:

• Biomechanics
• Exercise Physiology
• Sports Science

Background:

• Understanding muscle activation patterns during resistance exercises is crucial for optimizing training.
• Asymmetric loading in exercises like the bench press may elicit unique neuromuscular responses.
• Previous research has not fully elucidated the specific muscle engagement under varying degrees of asymmetric bench press loads.

Purpose of the Study:

• To compare the acute muscular activity of primary movers during bench press with asymmetric loads (25%, 50%, 75%).
• To investigate the effects of asymmetric loading on pectoralis major, triceps brachii, anterior deltoid, and external oblique activation.
• To analyze differences in muscle activity, barbell acceleration, and perceived exertion under various asymmetric bench press conditions.

Main Methods:

• Thirty resistance-trained males and females performed bench presses under seven different load conditions (including symmetric and asymmetric).
• Surface electromyography (sEMG) was used to measure peak muscle activity of the pectoralis major, triceps brachii, anterior deltoid, and external obliques.
• A repeated-measures design analyzed muscle activity, barbell center of mass acceleration, and OMNI-Perceived Exertion Scale (OMNI-RES).

Main Results:

• Significant effects of exercise condition were observed for muscle activity in both concentric and eccentric phases (p < 0.001).
• Higher pectoralis major activation (clavicularis and sternalis portions) was noted on the dominant side under high asymmetric (50%, 75%) de-loaded conditions during the eccentric phase.
• Contralateral external oblique muscles showed significantly high activation across all asymmetric conditions in the concentric phase (effect sizes from d = 0.89 to d = 2.30).

Conclusions:

• Asymmetric load bench press enhances pectoralis major activation on the loaded side when the contralateral side is de-loaded.
• The contralateral external oblique muscle activity can double under the most asymmetric loading conditions.
• These findings highlight the significant role of core stabilization and compensatory muscle recruitment during asymmetric resistance exercises.