Upper Body Muscles Anatomy

Major muscle groups of the upper body:

• Chest muscles: 

• Upper Chest
• Middle Chest
• Lower Chest 

• Shoulder muscles: 

• Anterior Deltoid
• Medial Deltoid
• Posterior Deltoid

• Biceps Brachii & Brachialis:
• Short Head
• Long Head
• Brachialis
• Triceps Brachii:
• Lond Head
• Medial Head
• Lateral Head
• Forearm muscles:
• Flexors
• Extensors
• Brachioradialis
• Abdominal muscles:
• Upper Abs
• Obliques
• Lower Abs
• Trapezius Muscles:
• Upper Fibers
• Middle Fibers
• Lower Fibers
• Back Muscles: 
• Rhomboid
• Lat Muscles
• Lower back (Erector spinae)

Chest muscles: 

The chest muscles, also known as the Pectoral muscles consist of Pectoralis minor and Pectoralis major. The primary function of these muscle groups is stabilization, depression, abduction, internal & downward rotation of the Scapula. 

• Pectoralis minor: This muscle can be found underneath the pectoralis major muscle.

• Pectoralis major: It is one of the most powerful muscles of the upper body which has two distinct muscle heads namely,

1. Clavicular head (Upper chest)
2. Sterno-Costal head (Middle & lower chest)

Shoulder muscles: 

The Shoulder muscles, which are also known as deltoid consist of three muscle heads namely Clavicular fibres, Acromial fibres & Spinal fibres. The function of these muscles is to rotate the arms and prevent dislocation of the shoulder joint when carrying heavy loads. Though the Deltoid muscle is used to rotate the arm along its joint, you can still target each muscle head individually as follows,

• Anterior head (Clavicular fibres): Anterior head can be targeted by raising your arms to your front, this helps to contract your anterior deltoid and expand when you bring your arms down.
• Medial head (Acromial fibres): Anterior head can be targeted by raising your arms to your side or by pushing your arms away from your body, this helps to contract your Medial deltoid and expand when you bring your arms down.
• Posterior head (Spinal fibres): Posterior head can be targeted by raising your arms to your side or by pushing your arms backwards, this helps to contract your Posterior deltoid and expand when you bring your arms to the standard position. 

Bicep Brachii & Brachialis:

The term "Bi" stands for two, which means that the bicep is made of two muscle fibres namely long head and short head.

The Brachialis is a separate muscle that is beneath the Biceps, unlike the Biceps the Brachialis muscle is connected to the elbow by its tendons. These muscles help in flexing the elbow along its joint.

• Short head: The short head muscle fibres originate from the Coracoid process of the scapula. 
• Long head: The short head muscle fibres originate from the Supraglenold tubercle of the scapula. 
• Brachialis: The Brachialis is a superficial muscle that is the main and strongest flexor of the elbow. 

Tricep muscles: 

The term "tri" represents three which means the tricep muscles consist of three fibres namely long head, medial head and lateral head. These muscles help in extending the elbow along its joint.

• Long head: It acts on the shoulder joint and is also involved in retroversion and adduction of the arms.

• Medial head: It enables more precise low-force movements. 

• Lateral head: It is used occasionally to handle high-intensity force.

Forearm muscles:

The muscles between your wrist and the elbow are called forearm muscles. The Forearm muscles consist of the following,

• Flexors

• Extensors

• Brachioradialis 

The Extensors can be further divided into superficial deep layers which helps to move the wrist, fingers and thumb individually.

Abdominal muscles: 

The abdomen is packed with three muscles namely obliques, upper abs and lower abs. The abdominal muscles support the trunk (torso), allow movement and hold organs in place.

• Upper abs: The top half of the abdominal muscles are called upper abs or upper Rectus Abdominis.

• Lower abs: The lower abs are the lower half of the abdominal muscles which are known as the lower Rectus Abdominis. 

• Obliques: The Obliques are two pairs of muscles that are located by the sides of the Rectus Abdominis namely,

1. External Obliques
2. Internal Obliques

Trapezius muscles:

The Trapezius or Trap muscles stabilize the shoulder blades and facilitate the shoulders & neck movements. The Trap muscles are separated into three sections namely,

• Upper fibres (Superior fibres): It helps to elevate the shoulder blades, rotate and tilt the neck.

• Middle fibres: The middle fibres help to move the shoulder blades backwards and also provide stabilization for the shoulder during some movements.

• Lower fibres (Inferior fibres): The lower back fibres helps to bring the shoulder blades to their low end. 

Back muscles: 

These muscles are one of the strongest muscles of the upper body which gives structural support to the trunk(torso). These muscles help to achieve pulling movements using your upper limbs. The Back muscles consist of the following,

• Rhomboid muscles: The Rhomboid muscles are located underneath the Trap muscles. The Rhomboids are a collective group of muscles namely,

1. Rhomboid major
2. Rhomboid minor

• Lat muscles: These are large V-shaped muscles that connect your arms to your vertebral column. These muscles assist all the pulling movements performed by the limbs.

• Lower back (Erector Spinae): These are some of the most important muscle fibres which help protect the Spine and to maintain stability.