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Muscle Biomechanics

TORSO FLEXION

1. Rectus Abdominis: Major belly muscle (six pack abs) running from front of the ribcage down to the pubic bone. ACTION: Bends the torso forward.

2. Obliques (internal and external): Side and waistline muscles which run from the side of the ribs diagonally to the top of the pelvic bones (ilium); internal fibers wrap posteriorly; external fibers wrap anteriorly. ACTION: Assist the rectus abdominis in bending the torso forward.

3. Iliopsoas: Psoas muscle runs from the lumbar vertebrae into the front surface of the pelvis (ilium), meets the iliacus muscle, then down to the inner upper leg (lesser trochanter) at the groin. ACTION: Bends the torso forward on the leg.

BACK EXTENSION

1. Erector Spinae Muscles: Back muscles run along the spine from neck to low back. ACTION: Arches the back, moves the torso backward in an arc.

2. Transversospinalis: Small and deep, there are 4 layers of these back muscles which connect the vertebrae from neck to low back. Here we are primarily interested in multifidus and rotatores. ACTION: Move the backbones (vertebrae) individually so the back is able to make a semi-symmetrical arch.

 

LATERAL FLEXION Side bending

1. Obliques: (internal & external) Side and waistline muscles which run from the side of the ribs diagonally to the top of the pelvic bones (ilium). Internal fibers wrap posteriorly; external fibers wrap anteriorly. ACTION: Pulls the (anterior) trunk down and to the side during side bending.

2. Quadratus Lumborum: On the back, running diagonally between top of the pelvis and lumbar vertebrae and ribs, this muscle lies under the erectors. ACTION: Pulls the trunk down and to the side during side bending.

3. Erector Spinae Muscles: Back muscles running along the spine from neck to low back. ACTION: Rotates the trunk.

4. Transversospinalis: Small and deep, there are 4 layers of these back muscles which connect the vertebrae from neck to low back. Here we are primarily interested in multifidus and rotatores. ACTION: Rotates spinal segments as well as individual vertebrae.

TORSO ROTATION

1. Erector Spinae Muscles: Back muscles run along the spine from neck to low back. ACTION: Trunk rotation.

2. Transversospinalis: Small and deep, there are 4 layers of these back muscles which connect the vertebrae of the spine from neck to low back. Here we are primarily interested in multifidus and rotators. ACTION: Rotates spinal segments as well as individual vertebrae.

3. Obliques: (internal & external) Side and waistline muscles which run from the side of the ribs diagonally to the top of the pelvic bones (ilium). Internal fibers wrap posteriorly; external fibers wrap anteriorly. ACTION: Opposite obliques act together to rotate the torso in both directions.

ABDOMINAL WRAPPING MUSCLES

1. Latissimus Dorsi: Looks like a fan, the largest back muscle lies on the surface and runs from the inner upper arm (bicipital groove) down to the mid and lower back. ACTION: Interdigitates with the obliques.

2. Lower Trapezius: Largest part of the trapezius muscles, this portion runs from the outer tip of the shoulder blade and fans out diagonally down to the middle spine (T5-12). ACTION: Pulls shoulder girdle downward.

3. Serratus Anterior: Large banana bunch muscle (likefingers) attaches to the inner edge (vertebral border) of the shoulder blade (near the spine) and fans out around the upper ribs. ACTION: Interdigitates with the obliques.

4. Obliques: (internal 6- external) Side and waistline muscles which run from the side of the ribs diagonally to the top of the pelvic bones (ilium). Internal fibers wrap posteriorly; external fibers wrap anteriorly. ACTION: Shares fascia with transversus abdominis.

5. Transversus Abdorninis: The deepest abdominal muscle, it runs horizontally between the ribcage and pelvic bone. It attaches in the front to the inguinal ligament and the pubis, the linea alba, and the abdominal fascia and in the back to the thoracolumbar aponeurosis. ACTION: Holds the viscera in place, stabilizes the space between ribs and pelvis.

SCAPULA ELEVATION

1. Levator Scapula: Runs diagonally from the inner upper (medial superior) border of the shoulder blade to the cervical spine (0-4) area. ACTION: Elevates the shoulder blade .

2. Upper Trapezius: Triangular shape running from outer tip of the shoulder blade fanning up to cervical spine area (occiput-C7). ACTION: Elevates the shoulder blade.

SCAPULA DEPRESSION

1. Lower Trapezius: Largest part of the trapezius muscle, this portion runs from the outer tip of the shoulder blade and fans out diagonally down to the middle spine (T5-12). ACTION: Rotates upward and pulls shoulder blade downward from its spine.

2. Pectoralis Minor: Runs diagonally between the front ribs (3,4,5) under the outer end of the collarbone to the scapula (coracoid process). ACTION: Pulls the upper shoulder blade downward and onto the ribcage.

SCAPULA ABDUCTION Protraction

1. Serratus Anterior: Large banana bunch muscle (likefingers) attaches to the inner edge (vertebral border) of the shoulder blade (near the spine) and wraps out around the upper ribs. ACTION: Hugs the shoulder blade against the ribcage.

2. Pectoralis Minor: Runs diagonally between the front ribs (3,4,5) and under the outer end of the collarbone to the scapula (coracoid process). ACTION: Pulls the upper shoulder blade downward and onto the ribcage.

SCAPULA ADDUCTION Retraction

1. Middle Trapezius: Triangular shape running from the outer tip of the shoulder blade and fanning out to the spine (TI-5). ACTION: Pulls the shoulder blade toward the spine.

2. Rhomboids: Run diagonally from the inner (medial) border of the shoulder blade up to the middle spine (U-T5). ACTION: Pulls the shoulder blade upward and inward toward the spine.

SCAPULA ROTATION Upward

1. Lower Trapezius: Largest part of the trapezius muscle, this portion runs from the outer tip of the shoulder blade and fans out diagonally down to the middle spine (T5-12). ACTION: Rotates outer tip upward.

2. Upper Trapezius: Triangular shape running from outer tip of the shoulder blade fanning up to cervical spine area (occiput-C). ACTION: Elevates and rotates the shoulder blade upward.

3. Serratus Anterior: Large banana bunch muscle (likefingers) attaches to the inner edge (vertebral border) of the shoulder blade (near the spine) and fans out around the upper ribs. ACTION: Assists in upward rotation of the outer tip of the shoulder blade.

SCAPULA ROTATION Downward

1. Levator Scapula: Runs diagonally from the inner upper (medial superior) border of the shoulder blade to the cervical spine (0-4) area, ACTION: Rotates the outer tip of the shoulder blade downward.

2. Rhomboids: Run diagonally from the inner (Medial) border of the shoulder blade up to the middle spine (U-T5). ACTION: Rotates outer tip downward.

3. Pectoralis Minor: Runs diagonally between the front ribs (3,4,5) under the outer end of the collarbone to the scapula (coracoid process). ACTION: Pulls the outer tip downward.

SHOULDER EXTENSION

1. Latissimus Dorsi: Looks like a fan, the largest back muscle lies on the surface and runs from the inner upper arm (bicipital groove) down to the mid and lower back. ACTION: Pulls the arm inward, down and backward.

2. Posterior Deltoid: Back of the shoulder cap, this muscle runs from the top of the shoulder blade (spine of scapula) down to the lateral side of the upper arm (humerus). ACTION: Moves the upper arm backward.

3. Teres Major: This small muscle connects the upper arm to the lower part of the shoulder blade. ACTION: Assists in moving the upper arm backward and rotating it internally.

SHOULDER ABDUCTION

1. Supraspinatus: Lies across the top of the shoulder blade. ACTION: Stabilizes top of upper arm (head of humerus) and lifts arm to side.

2. Middie Deltoid: Top of the shoulder cap, this muscle runs from the tip of the shoulder joint (mid acromion) down onto the upper arm (deltoid tuberosity). ACTION: Pulls the arm upward away from the body at the side.

SHOULDER ADDUCTION

1. Pectoralis Major: Big chest muscle attaches all along the breast bone and collarbone; narrows out to the inner upper arm (bicipital groove). ACTION: Assists in pulling the arm toward midline.

2. Latissimus Dorsi: Looks like a fan, the largest back muscle lies on the surface and runs from the inner upper arm (bicipital groove) down to the mid and lower back (attaches to spine and iliac crest). ACTION: Pulls the arm down toward midline.

INTERNAL SHOULDER ROTATION

1. Subscapularis: Covers the inner (subscapularfossa) portion of the shoulder blade (like a cushion to the ribcage) and attaches to the upper front of the arm (humerus) at the joint. ACTION: Rolls the upper arm forward and inward (medially).

2. Teres Major: This small muscle connects the upper arm to the lower part of the shoulder blade. ACTION: Assists in moving the upper arm backward and rotating it internally.

3. Latissimus Dorsi: Looks like a fan, the largest back muscle lies on the surface and runs from the inner upper arm (bicipital groove) down to the mid and lower spine. ACTION: Rotates the upper arm inward and forward.

4. Pectoralis Major: Big chest muscle attaches all along the breast bone and collarbone; narrows out the inner upper arm (bicipital groove). ACTION: Rolls the upper arm inward and forward.

5. Anterior Deltoid: front of the shoulder cap, this muscle runs from the collarbone to the lateral side of the upper arm (humerus). ACTION: Rotates the upper arm inward and forward.

EXTERNAL SHOULDER ROTATION

1. Infraspinatus: Covers most of the back portion of the shoulder blade and attaches to the upper outer arm (greater tubercle of the humerus). ACTION: Rotates upper arm backward.

2. Teres Minor: Sits above teres major and connects the middle outward edge of the shoulder blade to the back of the upper arm near the joint. ACTION: Rotates the upper arm (humerus) backward.

3. Posterior Deltoid: Back of the shoulder cap, this muscle runs from the top of the shoulder blade (spine of scapula) down to the lateral side of the upper arm (humerus) ACTION: Rolls the upper arm backward.

ROTATOR CUFF

1. Infraspinatus: Covers most of the back portion of the shoulder blade and attaches to the upper outer arm (greater tubercle of the humerus)). ACTION: Rotates and extends arm.

2. Supraspinatus: Lies across the top of the shoulder blade. ACTION: Stabilizes top of upper arm (head of humerus) and lifts arm out to side.

3. Subscapularis: Covers the inner (subscapularfossa) portion of the shoulder blade (like a cushion to the ribcage)and attaches to the upper front of the arm (humerus) at the joint. ACTION: Rolls the upper arm forward and inward (medially).

4. Teres Minor: Sits above teres major, connecting the middle outward edge of the shoulder blade to the back of the upper arm near the joint. ACTION: Rotates and pulls the upper arm (humerus) backward.

ARM FLEXION

1. Anterior Deltoid: front of the shoulder cap, this muscle runs from the collarbone to the lateral side of the upper arm (humerus). ACTION: Lifts the arm forward and upward.

2. Pectoralis Major: Big chest muscle attaches all along the breast bone and collarbone; narrows out to the inner upper arm (bicipital groove). ACTION: Assists in moving the arm forward and upward.

HORIZONTAL ARM ABDUCTION

1. Posterior Deltoid: Back of the shoulder cap, this muscle runs from the top of the shoulder blade (spine ofscapula) down to the lateral side of the upper arm (humerus). ACTION: Moves the upper arm backward in a horizontal plane.

HORIZONTAL ARM ADDUCTION

1. Anterior Deltoid: Front of the shoulder cap, this muscle runs from the collarbone to the lateral side of the upper arm (humerus). ACTION: Pulls the arm forward in a horizontal plane.

2. Pectoralis Major: Big chest muscle attaches all along the breast bone and collarbone, narrows out the inner upper arm (bicipital groove). ACTION: Moves the arm forward in a horizontal plane.

HIP FLEXION

1. Iliopsoas: Psoas muscle runs from the lumbar vertebrae into the front surface of the pelvis (ilium), then down to the inner upper leg (lesser trochanter) at the groin. ACTION: Bends the hip joint bringing the leg toward the pelvis.

2. TFL: Small lateral hip muscle running from (lateral iliac crest) top of pelvis into the IT band. ACTION: Assists in flexion, abduction and medial rotation of the hip as well as knee extension.

3. Pectineus: Diagonal muscle runs from the front of the pubic bone down to the back of thigh bone (fiemur) near the groin. ACTION: Flexes hip and assists in adduction and medial rotation of hip.

4. Rectus Femoris: Front of the thigh, (major quadriceps muscle) this muscle runs from the pelvis (AIIS) down to the knee cap (patella). ACTION: Assists in flexing the hip joint.

5. Sartorius: Runs from the front of the pelvis (ASIS) diagonally to medial lower knee (at the tibia). ACTION: Assists hip flexion, lateral rotation and abduction.

HIP EXTENSION

1. Gluteus Maximus: The outside layer and largest butt muscle, it attaches to the outer upper leg (gluteal tuberosity) and the middle of the lowest part of the back (sacrum atgluteal line). ACTION: Pulls the thigh bone backward.

2. Hamstrings: Back of the legs, these three muscles run from the sitting bones down to the back of the knees (bicepsfemoris runs to the lateral knee; semimembranosis and semitendinosus run to the medial knee). ACTION: Assist the glutes in pulling the thigh bone backward.

3. Quadratus Lumborum: On the back, running diagonally between top of the pelvis and lumbar vertebrae and ribs, this muscle lies under the erectors. ACTION: Stabilizes the lower back while the opposite leg is pulled backward as in walking.

HIP ABDUCTION

I.. Gluteus Medius and Minimus: Smaller than the maximus, these butt muscles run diagonally from the top back of the pelvis (Posterior ilium) down to the top of the outer leg (greater trochanter). ACTION: Pulls the leg away from midline.

2. Iliopsoas: Psoas muscle runs from the lumbar vertebrae into the front surface of the pelvis (ilium), then down to the inner leg (lesser trochanter) at the groin. ACTION: Assists in pulling leg away from midline.

2. TFL: This small muscle runs between the outermost part of the pelvis (lateral ilium) to the top of the leg (greater trochanter). ACTION: Assists in pulling leg away from midline.

HIP ADDUCTION

1. Adductor Brevis: Top most muscle running from the (anterior) pubic bone (near symphysis) to the upper (posterior) inner thigh. ACTION: Pulls the thigh down to midline.

2. Adductor Longus: Runs from the (anterior) pubic bone (near symphysis) just below Brevis to the upper (posterior) inner thigh. ACTION: Pulls the thigh down to the midline.

3. Adductor Magnus: Largest adductor, this muscle runs from the sitz bones to the (Posterior) thigh bone (attaches along femur between lesser trochanter and medial femur tubercle). ACTION: Pulls the thigh toward midline.

4. Pectineus: Diagonal muscle runs from the front of the pubic bone down to the back of thigh bone (Jemur) near the groin. ACTION: Assists in adduction.

INTERNAL HIP ROTATION

1. Gluteus Medius and Minimus: (lateral fibers) Smaller than the maximus, these butt muscles run diagonally from the top back of the pelvis (posterior ilium) down to the top of the outer leg (greater trochanter). ACTION: Rotates the thigh bone forward and inward.

2. TFL: This small muscle runs between the outermost part of the pelvis (lateral ilium) to the top of the leg (greater trochanter). ACTION: Assists in rotating the thigh bone forward and inward.

EXTERNAL HIP ROTATION

1. Piriformis: Lies underneath the gluteal muscles and runs from the inner lateral border of the low back (sacrum) to the top of the thigh bone (greater trochanter). ACTION: Rotates the thigh bone outward and back-ward.

2. Additional Deep Rotatores (5): Lie underneath the gluteal muscles and run between the middle portion of the low back (sacrum) and pelvis (ischium) to the top of the thigh bone (greater trochanter). ACTION: Assist the piriformis.

3. Iliopsoas: Psoas muscle runs from the lumbar vertebrae into the front surface of the pelvis (ilium), then down to the inner upper leg (lesser trochanter) at the groin. ACTION: Assists in external hip rotation.


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