Your upper arm isn't just biceps and triceps. There are several muscles working together to move your elbow and position your arm. Understanding all of them helps you build a complete, well-balanced arm.
Anterior Compartment (Front of Arm)
These muscles flex your elbow (bend your arm):
Biceps Brachii
• Location: Front of upper arm, superficial (close to skin)
• Function: Elbow flexion, forearm supination, minor shoulder flexion
• Two heads: Long head (outer) and short head (inner)
• How to train: Supinated curls of all types
Brachialis
• Location: Deep to biceps, on front of humerus
• Function: Elbow flexion only (pure flexor)
• Importance: Adds significant mass when developed
• How to train: Hammer curls, reverse curls
Coracobrachialis
• Location: Deep in the upper arm, near the armpit
• Function: Shoulder flexion and adduction
• Importance: Minor muscle, not trained directly
• Note: Works during pressing and front raises
Pro Tip
The triceps makes up about 2/3 of your upper arm mass. If you want bigger arms, don't neglect triceps training—it's arguably more important than bicep work.
Posterior Compartment (Back of Arm)
These muscles extend your elbow (straighten your arm):
Triceps Brachii
• Location: Back of upper arm
• Function: Elbow extension, shoulder extension (long head)
• Three heads: Long, lateral, and medial
Long Head:
• Starts at the shoulder blade (scapula)
• Crosses both shoulder and elbow
• Trained best with overhead movements
Lateral Head:
• Outer portion of triceps
• Creates the "horseshoe" shape
• Visible from the side
Medial Head:
• Deep head, mostly hidden
• Works during all elbow extension
• Important for complete triceps development
Anconeus
• Location: Small muscle near the elbow
• Function: Assists elbow extension
• Importance: Minor muscle, not trained directly
Muscles That Cross Into the Upper Arm
These originate elsewhere but affect the upper arm:
Deltoid
• Inserts on the upper humerus
• Affects arm position and shoulder movement
• Three heads: Anterior, lateral, posterior
Brachioradialis
• Technically a forearm muscle
• Originates on the lower humerus
• Assists elbow flexion
• Visible in the upper forearm near the elbow
Size Comparison
Relative sizes (approximate):
• Triceps: 60-65% of upper arm mass
• Biceps: 25-30% of upper arm mass
• Brachialis: 5-10% of upper arm mass
• Other: <5%
This is why tricep training is crucial for overall arm size.
Training All Upper Arm Muscles
For biceps:
Supinated curls (barbell, dumbbell, EZ bar)
For brachialis:
Neutral/pronated curls (hammer curls, reverse curls)
For triceps long head:
Overhead extensions, close-grip bench
For triceps lateral/medial heads:
Pushdowns, dips, close-grip pressing
For overall arm development:
• Balance pushing and pulling
• Include variety of grip positions
• Train with appropriate volume for each muscle
Complete Upper Arm Workout
Biceps:
1. Barbell curls: 3x10
2. Hammer curls: 3x12
Triceps:
1. Close-grip bench: 3x8-10
2. Overhead extensions: 3x12
3. Pushdowns: 3x15
This hits all the major upper arm muscles effectively.