What is a bi-acromial (between acromion processes) grip for chest press?

Bi-Acromial Grip for Chest Press

A bi-acromial grip (100% biacromial width) refers to hand placement on the barbell where the distance between your hands equals the distance between your two acromion processes (the bony points at the top of each shoulder).

Anatomical Definition and Measurement

• The biacromial distance is measured as the width between the acromion processes of both scapulae 1
• A 100% biacromial width grip means hands are positioned exactly shoulder-width apart, aligned with these bony landmarks 2, 3
• This represents the narrowest standardized grip commonly studied in chest press exercises 3, 4

Grip Width Variations in Research

Standard grip width classifications used in exercise science include:

• Narrow/Close grip: 100-120% of biacromial distance 3, 4
• Medium grip: 150-160% of biacromial distance 2, 4
• Wide grip: 200% of biacromial distance 2, 3, 4
• Self-selected grip: Typically averages 176% of biacromial distance 3

Performance Characteristics of Bi-Acromial Grip

Velocity and Displacement

• The bi-acromial (100-120%) grip produces significantly higher mean velocity and greater vertical bar displacement compared to wider grips 3, 4
• Peak velocity shows no significant differences across grip widths, but mean propulsive velocity is higher with narrower grips 4

Muscle Activation Patterns

• Triceps brachii: Significantly greater activation occurs at 50% biacromial width (16% MVIC) compared to 150% biacromial width (12% MVIC) 2
• Pectoralis major: Shows similar activation across grip widths, though clavicular portion may show slightly higher activity with neutral grip positions 2
• Anterior deltoid: Demonstrates comparable activation (~24% MVIC) regardless of grip width 2

Reliability Considerations

• The self-selected grip width (typically wider than bi-acromial) demonstrates superior reliability (CV ≤ 7.56%; ICC ≥ 0.82) compared to standardized narrow grips 3
• Medium grip width (150% biacromial) provides highest reliability for mean velocity measurements 3
• Peak velocity shows the highest overall reliability across all grip widths 3

Practical Application

The bi-acromial grip should be selected when:

• Maximizing triceps recruitment is the primary goal 2
• Greater bar velocity and displacement are desired 3, 4
• Training specificity requires narrow grip strength development 4

Avoid bi-acromial grip when:

• Shoulder pathology limits internal rotation or narrow positioning 1
• Testing requires maximum reliability, where self-selected grip is superior 3
• The trainee lacks technical proficiency with narrow grip mechanics 2