Kinesiology of Hip Muscles

Hip extensors sagittal plane

• Gluteus maximus

• Biceps femoris (long head)

• Hamstrings

• Adductor magnus (posterior head)

Hip flexors sagittal plane

• Iliopsoas

• Sartorius

• Tensor fascia latae

• Rectus femoris

• Adductor longus

• Pectineus

Iliopsoas actions

• Femur on pelvis

• Pelvis on femur

• Pelvic tilt vs hip osteokinematics

Iliopsoas effects of rotatory and translatory components of F_m

stability and mobility

Iliopsoas tendon deflection

Deflects posteriorly 45° over the acetabulum, increasing hip flexion leverage.

Iliopsoas moment arm at 90° hip flexion

ncreases, offsetting some force loss from active insufficiency.

Iliocapsularis

Keeps the anterior hip capsule taut to prevent impingement.

Additional iliopsoas actions

Assists with ER when the hip is abducted; stabilizes the lumbar spine bilaterally.

Iliopsoas tendinopathy

Repetitive tendon abrasion/impingement over the acetabulum or labrum; may cause snapping hip syndrome.

What unwanted movement can hip flexors cause?

Anterior pelvic tilt, increasing lumbar lordosis.

What muscles counteract anterior pelvic tilt during hip flexion?

Abdominals, which posteriorly tilt the pelvis.

What can excessive, chronic anterior pelvic tilt cause?

Increased lumbar lordosis, increased compression on lumbar facet joints, and increased anterior shear at the lumbosacral junction, potentially overstressing bone tissue.

any muscle capable of creating femoral-on-pelvic flexion is also capable of ______ tilting the pelvis

anteriorly tilting

How do the abdominals counteract hip flexors?

rectus abdominis creates posterior pelvic tilt to counteract anterior pelvic tilt.

What movement commonly accompanies femoral-on-pelvic hip flexion during walking and running?

Knee flexion to functionally shorten the lower limb.

What causes inefficient coactivation of the hip flexors and abdominals?

Weak abdominals with relatively strong hip flexors → excessive anterior pelvic tilt and lumbar lordosis, potentially causing low back pain (LBP).

How does posterior pelvic tilt affect the iliofemoral ligament?

Stretches the iliofemoral ligament, creating passive tension that biases the hip toward flexion.

Anterior pelvic tilt

stick butt out pelvis comes forward

Posterior pelvic tilt

stick butt in pelvis goes back

Which muscles control a slight forward bend of the trunk?

Hamstrings and gluteus maximus, with slight activation.

How does increased forward trunk lean affect hip extensor moment arms?

Increases the hamstrings’ moment arm but decreases the gluteus maximus’ moment arm, favoring hamstring use.

How does a hip flexion contracture affect muscle activation during standing?

Increases hip extensor activation because gravity creates a hip flexion torque, increasing the metabolic demands of standing.

Quad stretching

Recruit muscles to counteract RFs desire to APT in order to maximize stretch

Hamstring stretching

Contract muscles that counteract hamstrings desire to PPT in order to maximize stretch

Hip adductors frontal plane

• Primary

  • Pectineus

  • Adductor longus

  • Gracilis

  • Adductor brevis

  • Adductor magnus

• Secondary

  • Biceps femoris (long head)

  • Gluteus maximus (inferior fibers)

  • Quadratus femoris

  • Obturator externus

Hip abductors frontal plane

• Primary

  • Gluteus medius

  • Gluteus minimus

  • Tensor fasciae latae

• Secondary

  • Gluteus maximus

How do the adductors function in different hip positions in the sagittal plane?

In hip flexion, the adductors can extend the hip. In hip extension, the adductors can flex the hip

What is the function of the posterior portion of adductor magnus?

powerful hip extensor regardless of hip position.

When are most adductor muscles ineffective in the sagittal plane?

Around 40–70° of hip flexion, their lines of force pass through or near the medial-lateral axis of the hip.

What is the role of the multifidus during hip extension?

Provides a stable pelvis for the hip extensor muscles to pull against.

Why is the rectus femoris active during hip extension by the hamstrings?

Prevents excessive knee flexion by the hamstrings. Its hip flexion torque must be overpowered by the gluteus maximus and adductor magnus to effectively extend the hip.

Abductor muscles do what?

Control the pelvis in the frontal and transverse planes during gait, especially frontal plane during stance phase

What does HAT stand for?

head, arms, trunk

What is the effect of a trunk shift during single-limb stance?

• Places the center of mass of the HAT over the base of support.

• Helps maintain stability.

• Reduces hip abduction torque required.

How does side-to-side weight shifting affect the hip abductors?

Alters their moment arms and length-tension relationships.

When do hip abductors produce maximal torque?

When the hip is adducted just past neutral

Why does the gluteus medius have less force-generating ability in hip abduction?

Active insufficiency limits its ability to generate force and torque.

What does active insufficiency of the gluteus medius tell us about MMT positioning for hip abduction?

Position the hip in slight adduction, just past neutral, for optimal torque production.

In single-limb stance (SLS), how much force must the hip abductors produce, and why?

Hip abductors must produce a force twice that of body weight (BW) to achieve stability. The hip joint reaction force (JRF) balances the combined inferior forces of hip abductor weight (HAW) and BW.

How much is the hip joint reaction force (JRF) during activity?

Approximately 2.5× BW during walking and up to 5–6× BW during running or stairs.

Hip Internal rotator muscles

Primary: None

Secondary

• Gluteus medius and minimus (anterior fibers)

• Tensor fasciae latae

• Adductor longus

• Adductor brevis

• Pectineus

Internal rotation

• Adductors of hip as internal rotators due to bowing of the femur

• Linea aspera anterior to axis of rotation

• Adductor longus shown here with short MA

When are the IR muscles much more efficient at producing IR torque?

When the hip is at 90° flexion, which increases the transversely oriented component of the IR muscles.

How are the adductor muscles oriented when the hip is at 90° flexion?

Almost perpendicular to the superior/inferior (S/I) axis.

Hip > 90 degrees Flexion

• Piriformis & anterior fibers of gluteus maximus switch actions

  • contribute to IR at > 90° hip flexion

• Hip IR strength ~50% greater with hip flexed

Hip external rotators transverse plane

Primary

• Gluteus Maximus

• Piriformis

• Obturator internus, superior and inferior gemelli, quadratus femoris

Secondary

• Gluteus medius and minimus (posterior fibers)

• Obturator externus

• Sartorius

• Biceps femoris (long head)

• Iliopsoas if hip in Abducted position

Short Hip External Rotators

PGOGOQ

External rotation

Obturator internus uses lesser sciatic notch like a pulley. Also important for compressive forces at the joint. Deep ER act similarly to infraspinatus and teres minor at the shoulder

Hip Joint Compression During Gait

• Articular surfaces of femoral head and acetabulum superiorly are the thickest

• Forces in acetabulum vary from 13% of body weight during swing phase to >300% during midstance

How does using a straight cane in the contralateral UE affect hip abductor force and joint compression?

A straight cane provides an abduction torque during stance, reducing the force required from the hip abductors and the compressive forces at the joint.

Why is using a straight cane in the contralateral UE helpful for patients with weak hip abductors or hip OA?

It reduces the internal torque required by the hip abductors, decreasing the demand on weak muscles and reducing compressive forces at the hip joint in patients with osteoarthritis (OA).

Carrying contralateral loads can significantly increase _____

external hip adduction torque, causing increased load on hip abductors

Joint forces

• Contact force during stance phase of gait is 3x times body weight

• Use of a cane can lessen the joint forces by 40% (Brand 1980)

• Reducing cadence also reduces force

• Carrying packages on affected side reduces force

Lateral trunk bending

• Lateral trunk bending results in the following:

  • Minimal hip abductor activation on the ipsilateral hip

What is the Trendelenburg sign associated with?

Weakness of the hip abductors.

What happens during a positive Trendelenburg sign?

When standing on one foot, the pelvis drops on the unsupported side.

What movement is usually accompanied by a positive Trendelenburg sign?

Lateral deviation of the trunk.

What is the actual “sign” in the Trendelenburg sign?

The dropping of the pelvis, not the trunk deviation.