Skeletal Muscle Anatomy and the Body's Main Muscles

Introduction

It's estimated that there are over 650 named skeletal muscles in the human body, which can be categorised into three types: skeletal, smooth, and cardiac. Skeletal muscles can be controlled voluntarily, while smooth muscles are involuntary and found in organs. Cardiac muscle makes up the heart.

Neuromuscular System

The brain, spinal cord, nerves and skeletal muscles work together to cause movement – collectively known as the neuromuscular system. At its core, this system enables the body to respond to stimuli and perform various physical activities.

The neuromuscular system's primary function is to control voluntary movements. When the brain decides to initiate a movement, it sends electrical signals through the nerves to the relevant skeletal muscles.

These signals cause the muscles to contract, resulting in movement. In addition to facilitating voluntary movements, the neuromuscular system plays a role in maintaining posture and balance and enabling reflex actions. The interaction between the brain, muscles, and sensory feedback enables the body to adapt to various physical activities and environments.

Superficial and Deep Muscles

Superficial and deep muscles refer to the muscles' layers at different depths in the body.

Superficial Muscles

These are the muscles located closest to the body's surface. They are typically more visible and responsible for more substantial and noticeable movements. Superficial muscles can include major muscles like the biceps, triceps, deltoids, and pectorals, which are primarily involved in movements of the limbs and torso. Because they are closer to the skin, they can also play a role in posture and overall body shape.

Deep Muscles

 In contrast, deep muscles are located beneath the superficial muscles and are often smaller and more intricate. They are critical in stabilising joints, supporting posture, and assisting with finer movements. These include the rotator cuff muscles, the intrinsic muscles of the hands and feet, and deep core muscles such as the transverse abdominis. Deep muscles work with the superficial muscles to facilitate coordinated movement and stability. We will focus on the superficial muscles rather than the deep tissue muscles.

Major Skeletal Muscles

I separate the major muscles into two categories to keep it simple: upper and lower body muscles. Some might categorise them into the upper and lower limbs and anterior and posterior trunks, but let’s keep it simple.

Twelve Major Upper Body Muscles

1. Deltoid (shoulders)

2. Biceps Brachii

3. Triceps Brachii

4. Trapezius (Trap’s)

5. Latissimus dorsi (Lat’s)

6. Rectus Abdominus (Ab’s)

7. External Oblique

8. Pectoralis (Chest, also known as Pecs)

9. Forearm Group (two muscles together)

10. Teres Major and Minor

11. Rhomboid Major and Minor

12. Levator Scapulae

Six Major Lower Body Muscles

1. Quadriceps (four muscles together)

2. Hamstring Group (three muscles together)

3. Gluteus Maximus (three muscles grouped)

4. Calves (Gastrocnemius, Soleus and Tibialis anterior)

5. Adductors

6. Sartorius

It's important to note that I have grouped major muscles into one to simplify it further, such as the calves, quadriceps, and Hamstrings. If you want a fancier breakdown based on whether the major muscle falls into limbs or trunk, it is as follows:

Major Muscles of the Upper Limb (Arms)

• Deltoid

• Rotator Cuff Muscles

• Biceps Brachii

• Triceps Brachii

• Brachialis (located underneath the biceps)

• Forearm (Flexor and Extensor Group) 

• Hand Muscles

 

Major Muscles of Lower Limb (legs)

• Quadriceps (four muscles together)

• Hamstring Group (three muscles together)

• Gluteus Maximus

• Calves (Gastrocnemius, Soleus and Tibialis anterior)

• Sartorius

Major Muscles of Trunk – Anterior

• Pectoralis

• Rectus abdominous

• External oblique

Major Muscles of Trunk – Posterior

• Trapezius (upper back)

• Latissimus Dorsi

• Rhomboids (major and minor)

• Teres Major and Minor

• Levator Scapulae

Trunk = the part of the body to which the head, arms, and legs connect.

The JH Six Categories

1. Pectoralis (Chest Muscles)

2. Back (Rhomboids, Lat’s, Trap’s, Teres major and minor, Spinae erector)

3. Arms (Bicep, Forearms and Tricep muscles)

4. Core (Abdominal and oblique muscles)

5. Legs (quadriceps, hamstrings, calves and Gluteals, and abductors)

6. Deltoids (Shoulder Muscles)

Important Note: from now on, I will omit a few major muscles that don’t need to be discussed:

• Sartorius

• Hand Muscles

• Rotator Cuff Muscles

Pectorals (Chest Muscles)

The pectorals, the leading muscle group of the chest, are not just large muscles in the chest; they are also the powerhouse behind upper body movements. Their role in shaping the torso is just one aspect of their significance.  These muscles connect the front of the human chest to the upper arm and shoulder bones. As seen in the figure below, the pectorals consist of two main parts: the Pectoralis Major and the Pectoralis Minor.

The Pectoralis: Credit Bereact.com

Pectoralis Major

The pectoralis major, a large, fan-shaped muscle at the front of the chest, is not just a muscle but a marvel of human anatomy. Its role in various arm movements is a testament to the intricate design of the human body. The Pectoralis Major consists of two parts:

1. Clavicular Head: This part originates from the clavicle, commonly referred to as the collarbone. It helps flex the arm and move it inward toward the body.

2. Sternal Head: This part comes from the sternum (breastbone) and goes to the humerus (the upper arm bone). It helps bring the arms closer to the body and allows them to rotate.

Pectoralis Major Heads (Credit: teachmeanatomy.com

The pectoralis Major's three key functions

1. Shoulder Flexion: Raising the arm forward is critical in exercises like the bench press.

2. Shoulder Adduction involves bringing the arms toward the body’s midline, which is especially important in pushing movements, such as push-ups.

3. Internal Rotation of the Shoulder: This helps stabilise the shoulder joint during various lifts.

Pectoralis Minor

The pectoralis minor is smaller and located under the pectoralis major. It starts from the third, fourth, and fifth ribs and attaches to the coracoid process of the scapula (shoulder blade).

The pectoralis minor is a small, triangular muscle located beneath the larger pectoralis major in the chest. It originates from the third to fifth ribs and attaches to the coracoid process of the scapula (shoulder blade).

Pectoralis Minor (Credit: bodyworksprime.com)

The pectoralis minor plays a crucial role in shoulder health and posture. It stabilises the scapula by pulling it forward and downward, essential for maintaining good posture and preventing shoulder injuries. It also assists with shoulder movements, like lifting the arms, making it a vital muscle to target in your training routine.

Functions of the Pectoralis Minor in Weightlifting

1. Stabilising the Scapula: As it connects to the shoulder blade (scapula) and the ribs, it helps keep the scapula stable during weightlifting movements. In addition, it plays a vital role in safe shoulder movements in exercises such as the bench press and overhead press.

2. Safe Shoulder Movement: It helps shoulder blades move forward and down and rotate downwards safely.

3. Injury Prevention: a strong pectoralis minor protects the shoulder from injuries; if it's weak or tight, it can affect the shoulder's movement, leading to injuries during pressing movements.

4. Assisting in Pushing Movements: While the pectoralis major is the main muscle in pushing exercises, the pectoralis minor also helps. It supports motion and stability during exercises like the bench press.

The Back Muscles

The back muscles are crucial for maintaining posture, facilitating movement, and supporting the spine. They can be classified into three main groups: superficial muscles, intermediate muscles, and deep muscles. The main back muscles in this grouping are:

1. Rhomboid Major and Minor

2. Trapezius

3. Latissimus dorsi

4. Rhomboid Major and Minor

5. Teres Major and Minor

6. Erector Spinae

Major Back Muscles

Trapezius

This large, triangular muscle extends from the back of the skull down the vertebral column to the thoracic spine and laterally to the scapula. It is responsible for shoulder girdle movements, including elevation, retraction, and rotation of the scapula. The trapezius muscle can be divided into three distinct parts based on their location and function, as seen in the image below.

Three Sections of the Trapezius (Credit: baselinehealing.com)

1.  Upper Trapezius: This portion runs from the skull's base to the clavicle's outer third. It primarily elevates the shoulder blades and assists in rotating the neck.

2.  Middle Trapezius: Located between the upper and lower sections, this part extends from the upper back and connects to the acromion and spine of the scapula. It is mainly responsible for retracting the shoulder blades, bringing them closer together.

3. Lower Trapezius: This segment goes from the spine of the scapula to the lower thoracic vertebrae. Its primary function is to depress the scapula and assist in upward rotation.

Latissimus Dorsi

 Located in the lower back, this broad muscle extends from the mid-to-lower spine to the front of the body. In the weightlifting world, it is abbreviated to ‘Lat’s. '. This muscle pulls the arms downward, backwards, and toward the body. In addition to its role in movement, the Latissimus Dorsi helps stabilise the spine and pelvis during physical activities.

Latissimus Dorsi

You might see in bodybuilding literature that the lats have three sections: upper, middle, and lower. This is more commonly used to categorise Lat exercises, as some target specific sections of the Lat more than others. This could be done by adjusting the grip positioning for the Lat Pulldown exercise. Some say that Wide Grip Lat Pulldowns target the upper Lats more, and Close Grip Lat Pulldowns target the lower Lats, meaning grip positioning will affect which section of the Lat is targeted more.

Straight-arm pulldowns, Lat Dumbbell Pullovers, and Dumbbell Rows are said to target the lower lats more, while exercises such as T-bar rows, Seated Cable Rows, Inline Dumbbell Rows and Landmine Rows target the upper Lats more.

Latissimus Dorsi Three Sections

The best Lat exercises to isolate the Lat’s are:

• Lat Pulldowns (close grip/wide grip and underhand grip variations)

• Bent over Rows (Barbell or Dumbbell)

• Hammer Strength Rows

• Dumbbell Lat Pullover

• Incline Dumbbell Rows

Rhomboid Major and Minor

These muscles are located between the spine and the scapula and are responsible for retracting the scapula (pulling the shoulder blades together). The rhomboid muscles, which include the rhomboid major and the rhomboid minor, are a pair of muscles located in the upper back, beneath the trapezius. They are crucial in stabilising the scapula (shoulder blade) and various shoulder movements.

Rhomboid Major and Minor (Credit: University of Washington)

Rhomboid Major

The rhomboid major is a critical upper back muscle underneath the trapezius. It is shaped like a diamond and is vital in maintaining proper posture and stabilising the Scapula (shoulder blades).

Scapula (Credit: https://orthoinfo.aaos.org/)

This muscle is primarily responsible for retracting the scapula (pulling it towards the spine), elevating it, and rotating it to allow for better shoulder mobility. It helps with movements like pulling the shoulders back during rowing exercises.

Rhomboid Minor

 The Rhomboid Minor runs from the spine to the shoulder blade. It is the smallest of the two Rhomboids and, thus, commonly overlooked. Its primary function is connecting the scapula to the spinal column's vertebrae.

It is located deep to the trapezius and superior to the rhomboid major. However, the Rhomboids are commonly overlooked in hypertrophy training, as the lats and traps tend to take the focus.

Common exercises used to isolate the Rhomboids are:

• Face Pulls

• Bent-over-Rows

• Chest Supported Dumbbell Row

• Shrugs

Levator Scapulae

The levator scapulae is a small yet significant muscle at the back and side of the neck. Its primary function is elevating the scapula (shoulder blade), which is critical in shoulder movement and posture. The levator scapulae are essential for raising arms or shoulder movements, such as reaching overhead or lifting objects.

Strengthening this muscle contributes to better shoulder function and can help prevent injuries, especially in tasks involving overhead work or repetitive shoulder motions. Ensuring that the levator scapulae remains strong and flexible is vital for shoulder health and upper body mobility.

Exercises commonly used to train the Levator Scapulae are:

• Deadlift

• Shrugs

• Farmers Carry

Teres Major and Minor

The Teres major and minor muscles are deep back muscles commonly overlooked in hypertrophy training. Bigger brothers and sisters, such as deltoids, trapezius, and lats, dwarf them. The illustration below shows their positioning and how they can be overlooked in training.

Teres Major and Minor

Infraspinatus

I will also include in this section the infraspinatus, a robust, small triangular muscle at the shoulder joint's back. As one of the four muscles comprising the rotator cuff located at the back of the shoulder blade, it rotates the humerus externally and stabilises the shoulder joint externally. This is a deep muscle, not superficial.

Teres Major

The teres major is a thick, rounded muscle located on the posterior aspect of the shoulder. It originates from the posterior surface of the inferior angle of the scapula and inserts into the medial lip of the bicipital groove of the humerus. 

The teres major is responsible for several vital movements at the shoulder joint, including adduction (bringing the arm towards the body), medial rotation (turning the arm inward), and extension when the arm is elevated. It stabilises the shoulder joint, working alongside other muscles to ensure proper arm function. Exercises such as the following can target and engage the Teres Major during training:

• T-Bar Rows

• Chin-ups

• Lat Pulldowns

• Pull-ups

• Bent-Over Dumbbell Row (Uni-Lateral)

• Seated Uni-Lateral Row

• Seated Cable Row

  
  

Teres Minor

The Teres Minor is a smaller muscle in the upper back, just above the teres major. It originates from the lateral border of the scapula and inserts into the greater tubercle of the humerus.

The Teres Minor primarily assists in lateral rotation of the arm, as well as helping in adduction. It is one of the four rotator cuff muscles crucial for shoulder stability. Exercises to strengthen and isolate the Teres Minor are:

• External rotation exercises (e.g., with bands or cables)

• Shoulder stabilisation exercises

• Side-lying external rotation

Shoulder (Deltoids)

The deltoid muscles are large, triangular-shaped muscles that cover the shoulder joint. They enable you to move your arm in various directions, such as raising it sideways.

Three Deltoids (Credit: https://kinxlearning.com/)

The deltoids also serve as the primary muscles that stabilise the shoulder joint, connecting the collarbone (clavicle), shoulder blade (scapula), and upper arm bone (humerus). The deltoids are split into three areas:

1. Anterior Deltoid (Front Deltoids)

2. Posterior Deltoid (Rear deltoids)

3. Lateral Deltoid (Mid Deltoids)

Anterior Deltoid (Front)

The anterior deltoid originates from the lateral third of the clavicle (collarbone) and primarily assists in shoulder flexion (raising the arm forward) and internal rotation. It also aids in shoulder abduction when the arm is raised. In training, one would perform dumbbell, cable, or barbell front raises to isolate the anterior deltoid.

Posterior Deltoid (Rear)

The posterior deltoid, which originates from the spine of the scapula, assists in shoulder extension (raising the arm backwards) and external rotation. It helps maintain balance in shoulder movements, especially when pulling motions are involved. To isolate the posterior deltoid in training, one would perform dumbbell, cable, or machine rear deltoid flies.

Deltoid Points of Origin

Lateral Deltoid (Mid)

The lateral deltoid, which originates from the acromion process of the scapula (shoulder blade), is pivotal for shoulder abduction (raising the arm sideways). It is most active when lifting the arm to the side, making it essential for lateral movements. To isolate the lateral deltoid in training, one would perform dumbbell, cable or machine side lateral raises typically with a 45-degree flexion in the elbow.

The deltoids work synergistically with other shoulder muscles, such as the rotator cuff, to provide a wide range of motion while maintaining shoulder stability. They are involved in numerous activities, including lifting, pushing, pulling, and throwing.

The versatility of the deltoids in providing a wide range of motion is a testament to the complexity of the shoulder joint. The strength and coordination of the deltoids are vital for performing exercises like overhead presses, lateral raises, and various sports activities.

The best compound deltoid shoulder exercises that one could perform in training would be:

• Military Overhead Press (Strict overhead press, no leg drive)

• Seated Dumbbell Shoulder Press

Arms (Bicep and Tricep Muscles)

Bicep Brachii Muscle

The biceps are located at the front of the upper arm. The biceps, specifically the biceps brachii, are a pair of muscles located at the front of the upper arm. Each bicep has two parts, or “heads,” called the long and short heads. These muscles are primarily responsible for flexing the elbow and turning the palm upward, a motion known as supination.

In addition to bending the elbow, the biceps aid in shoulder movements, including lifting and raising the arm sideways.  They play a critical role in various daily activities, such as lifting objects and performing pulling motions. Biceps are typically perceived to symbolise that don't contribute strength in pop culture(big-arm guys are muscular!). However, they are small muscles that don't contribute much to overall body strength and can be fragile when performing heavy pull movements.

Bicep (Credit: https://biqbandtraining.com/)

Long Head

To emphasise the long head during training, use exercises that involve shoulder flexion, such as incline bicep curls or incline dumbbell curls where the arms are positioned behind the body. Additional exercises targeting the long head more than the short head are Hammer Curls, Drag Curls, and the Close Grip Barbell Curl.   

Short Head

To emphasise the short head, use exercises where the arms are in front of the body, such as concentration or preacher curls. Additional exercises one could use to isolate the short head more than the long head are the high Cable Curls and the Wide Grip Bicep Curl.

Brachialis

The brachialis is one of the largest muscles involved in elbow flexion and solely facilitates forearm flexion at the elbow. It serves as a primary flexor of the forearm at the elbow joint, enabling elbow flexion in all positions. Its large cross-sectional area provides it with more strength than the biceps brachii.

The forearm should be in pronation to isolate the brachialis muscle because the biceps brachii acts as a supinator and flexor. Pronating the forearm places the biceps at a mechanical disadvantage (see the illustration below to understand supernation and pronation).

Supernation and Pronation

Tricep Brachii Muscle

The triceps brachii, commonly known as the triceps, is a large muscle at the back of the upper arm. It helps stabilise the shoulder joint and straighten the elbow joint. The triceps brachii consists of three distinct heads: the long head, lateral head, and medial head, each playing a crucial role in arm movement and stability. The primary function of the triceps muscle is to extend the elbow joint, straightening the arm from a bent position.

Tricep Brachii Heads (Credit: https://philamassages.com)

Long Head

The Long Head runs along the back of the arm and involves shoulder and elbow extension. It plays a crucial role in elbow extension and shoulder stability. By isolating and targeting the long head in the Tricep with exercises such as Dumbbell, Cable, or Barbell Overhead Extensions, you can ensure the health and stability of your shoulder joint.

Lateral Head

The primary function of the lateral head of the triceps is elbow extension, which involves straightening the arm at the elbow joint.  It helps stabilise the elbow joint during various activities involving arm movement.

The lateral head is best isolated with exercises whereby the arms are at the sides with an overhand grip, such as Cable Press-downs and Tricep Dips whereby the elbows are close to the body to emphasise the lateral head. In addition, when appropriately performed, Lying Triceps Extension with an EZ Curl barbell can effectively engage the lateral head. The Close-Grip Bench Press activates the lateral head significantly and trains the other two heads.

Medial Head

The medial head of the triceps brachii is one of three heads that make up the triceps muscle located at the back of the upper arm. The triceps are primarily responsible for elbow extension, and the medial head plays a significant role in this movement.

The medial head originates from the posterior surface of the humerus, below the radial groove. Unlike the other heads, it does not attach to the shoulder girdle. It inserts into the olecranon process of the ulna, which is the bony prominence at the back of the elbow. It is particularly active during heavy lifting and when the arm is in a neutral or slightly flexed position. The medial head contributes to the overall stability of the elbow joint.

To effectively engage and strengthen the medial head of the triceps, use exercises whereby the arms are at the sides with an underhand grip, such as Reverse Grip Press-downs, reverse grip floor press, and dumbbell or barbell reverse grip press.

Forearm Muscles

Many people are surprised to learn that the forearm muscles are vast and complicated. Twenty muscles are located in this region and divided into the anterior and posterior compartments of the forearm. The forearm consists of flexor and pronator muscles and can be divided into deep and superficial muscles. The figure below shows many muscles within just a small section of the body.

Forearm Muscles

Flexor vs. Extensor Simple

To simplify, I will categorise the muscles in the posterior or anterior of the forearm as either flexor or extensor. Flexor muscles reduce the angle between bones, helping us bend our elbows and fingers. Extensor muscles increase the angle between bones, allowing us to straighten or extend.

Anterior Forearm Muscles

The anterior forearm consists of seven muscles, five superficial and three deep. As seen below, we will keep it simple and lump them all into one group: flexor and extensor muscles on the anterior section of the forearm. The core role of the anterior section of the forearm is flexion of the forearm at the elbow joint and adduction of the arm at the shoulder joint.

Superficial Anterior Muscles

Deep Anterior Forearm Muscles

Posterior Forearm Muscles

The posterior forearm muscles primarily consist of extensor muscles. Like the anterior section of the forearm, the posterior forearm can be divided into superficial and deep muscle groups. The Posterior forearm section has 12 muscles: seven superficial and five deep. The posterior section of the forearm muscles produces wrist and or finger extension and thumb abduction.

Superficial Posterior Muscles

Deep Posterior Muscles

Overall, the deep posterior forearm muscles are essential for various activities that require fine motor skills and hand strength. The best forearm exercises to target and engage them are:

• Dumbbell or Barbell Wrist Curls

• Reverse Wrist Curls

• Hammer Curls

• Reverse Grip EZ Bar Curls

• Farmers Carry

• Towel Pull-ups

Abdominal Muscles (Including Oblique)

Abdominal Muscles

The abdominal muscles, commonly called the "abs," are a group of muscles located in the front of the torso. They are critical in core stability, movement, and overall posture. Understanding the different muscles within the abdominal region can help enhance strength training and injury prevention. Here’s a breakdown of the main abdominal muscles:

Rectus Abdominis (Lower Abs)

This is the most well-known abdominal muscle, often called the "six-pack" because of its segmented appearance in well-defined individuals. It runs vertically along the front of the abdomen, stretching from the pubic bone to the sternum.

The rectus abdominis is primarily responsible for flexing the spine, which allows for movements like bending forward and performing sit-ups. It also supports the internal organs and contributes to postural alignment. Exercises that isolate the Rectus Abdominis are Leg raises, Reverse Crunches, or flutter kicks. Crunches are generally the go-to exercise for the rectus abdominis.

Obliques (Side Abs)

 The oblique muscles consist of two main groups: external and internal. These muscles are located on the sides of the abdomen and play a crucial role in rotational movements and lateral flexion of the torso.

1. External Obliques: The larger outer muscles run diagonally from the lower ribs to the pelvis. They rotate the trunk and bend it sideways.

2. Internal Obliques: These are located beneath the external obliques and run in the opposite diagonal direction. They assist in trunk rotation and lateral flexion and support the abdominal wall.

The exercises most commonly used to isolate the obliques are side bends with dumbbells or cable machines, bicycle crunches, Russian twists, and side planks.

Transverse Abdominis (More Mid-Section Abs)

This is the deepest layer of the abdominal muscles, running horizontally across the abdomen. It acts like a natural corset by stabilising the core and supporting the spine. The transverse abdominis helps maintain intra-abdominal pressure, which is vital for lifting and heavy exercise.

Strengthening this muscle can improve stability and overall athletic performance. The exercise that best emphasises the Transverse Abdominis would be the plank, whether elbow plank, side plank, or high plank.

Legs Muscles

Leg muscles can be categorised into four groups:

1. Quadriceps

2. Hamstrings

3. Calves

4. Gluteus Maximus

   
   

Quadriceps

Quadricep

The quadriceps, commonly known as the "quads," are a group of four muscles located at the front of the thigh.

They are vital for extending the knee, everyday activities, and athletic performance. Strong quads support the knees and help prevent injury. 

There are four muscles of the Quadriceps:

• Rectus Femoris (Mid)

This muscle is located in the middle of the thigh and runs down the length of the thigh. It is unique among the quadriceps as it crosses both the hip and knee joints, allowing it to assist in hip flexion and extension.

• Vastus Lateralis (Outer)

Located on the outer side of the thigh, the vastus lateralis is the largest component of the quadriceps group. It primarily aids in extending the knee and stabilising the patella (kneecap).

• Vastus Medialis (Inner)

Positioned on the inner part of the thigh, the vastus medialis helps with knee extension and plays a critical role in stabilising the patella, especially during activities that require changing directions or loading the knee.

• Vastus Intermedius

 This muscle lies underneath the rectus femoris and also contributes to knee extension. It is less visible but plays an essential role in overall quad strength.

The most commonly used exercises to isolate and strengthen the quadricep are:

• Leg Extensions

• Narrow Stance Leg Press

• Step-ups

• Goblet Squats

• Front Squats

• Forward Lunges

Hamstrings

The hamstring muscles are a group of three muscles located at the back of the thigh. They play a crucial role in hip and knee movement. The primary function of the hamstring muscles is to bend the knee, bringing the heel toward the buttocks.

Hamstring

During activities like running and cycling, the hamstrings help extend the hip joint, moving the thigh backwards. The hamstrings help stabilise the pelvis and upper body during various movements, helping maintain balance. The three muscle groups are:

• Biceps Femoris

This muscle has two heads—long and short. The long head originates from the ischial tuberosity of the pelvis, while the short head originates from the femur. Both heads are inserted into the fibula. The biceps femoris is responsible for flexing the knee, extending the hip, and laterally rotating the leg when the knee is bent.

• Semitendinosus

This muscle is located between the biceps femoris and the semimembranosus. It originates from the ischial tuberosity and inserts into the upper part of the medial surface of the tibia. The semitendinosus aids in flexing the knee, extending the hip, and medially rotating the leg.

• Semimembranosus

 The semimembranosus lies underneath the semitendinosus. It also originates from the ischial tuberosity, but its insertion is on the medial condyle of the tibia. This muscle assists in knee flexion, hip extension, and medial leg rotation.

The most commonly used hamstring exercises used to isolate, build and strengthen this muscle are:

• Stiff-Legged Deadlift

• Hamstring Curls

• Romanian Deadlift

• Assisted Glute Hamstring Raises (GHR)

Maintaining flexibility and strength in the hamstring muscles is essential for overall leg function. Tight hamstrings can lead to a higher risk of injuries, such as strains or tears, particularly in sports that require sprinting or powerful leg movements.

Hamstring injuries are common among athletes and can occur during activities that involve sudden acceleration or deceleration. Symptoms of a hamstring strain include pain, swelling, and bruising at the back of the thigh. Proper warm-up, stretching, and strength training can reduce the risk of hamstring injuries.

Calves

The calf muscles comprise two major muscle groups: the gastrocnemius and the soleus. These muscles are located at the back of the lower leg and play crucial roles in movement and stability. The calve muscles are as follows:

Calve Muscles (Credit: Cleveland Clinic)

• Gastrocnemius

The gastrocnemius is the larger and more superficial of the two calf muscles, giving the calf its rounded appearance. It has two heads (medial and lateral) that originate from the femur just above the knee joint. This muscle is primarily responsible for plantar flexion of the foot (pointing the toes) and plays a vital role in running, jumping, and walking activities. It also assists in flexing the knee, making it essential for any movement involving the legs.

• Soleus

The soleus is located beneath the gastrocnemius and has a flat, broad shape. It originates from the lower leg's tibia and fibula (the bones) and connects to the Achilles tendon. The soleus is also responsible for plantar flexion but is particularly active during activities when the knee is bent, such as cycling or rowing. It is crucial for maintaining posture and balance, especially when standing.

• Achilles Tendon

The gastrocnemius and soleus muscles insert into the Achilles tendon, which attaches to the heel bone (calcaneus). The Achilles tendon plays a vital role in locomotion, allowing the force generated by the calf muscles to propel the body forward.

The two go-to exercises for isolating and targeting the calve muscle are the Seated Calf Raises, which tend to target the soleus more than the gastrocnemius, and the Standing Calf Raises. 

Gluteus

The gluteus muscles, commonly called the glutes, are a group of three muscles located in the buttocks. These muscles are crucial for various movements and play a significant role in maintaining overall mobility and stability.

Gluteus Muscle

The gluteal muscles are essential for various physical activities, including walking, running, jumping, and squatting. Well-developed glutes contribute to better athletic performance, power generation, and injury prevention, particularly in the lower back, hips, and knees.  The three muscles that make up the glutes are:

• Gluteus Maximus

 This is the largest and most powerful muscle in the group. Its primary function is to extend and externally rotate the hip joint, which is vital in movements such as standing up from a seated position, climbing stairs, and sprinting. The gluteus maximus also helps maintain upright posture and stability during hip movement activities.

• Gluteus Medius

Located underneath the gluteus maximus, the gluteus medius's primary functions include abducting the hip (moving the leg away from the body's midline) and internally rotating the hip. It is crucial for stabilising the pelvis during walking or running, preventing the pelvis from dropping on the opposite side.

• Gluteus Minimus

The smallest of the three gluteal muscles, the gluteus minimus, lies underneath the gluteus medius. Like the gluteus medius, its primary functions involve hip abduction and internal rotation. It assists in stabilising the pelvis and works with its larger counterparts to ensure proper movement mechanics.

Exercises commonly used to isolate, strengthen and grow the glutes are:

• Hip Thrusts

• Squats

• Glute Bridges

• Lateral Side-Step (using resistance bands is optimal)

• Lateral Step-ups

• Sumo Deadlifts

• Glute Kickbacks

• Cable Pull-throughs