The pelvis is made up of 6 bones:
- 2 ilium
- 2 ischium
- 2 pubic bones
These all come together at the sacrum to form a ring shape, which also connects to the hip joint. Muscles and ligaments surround the pelvis to keep it stable as the rest of our body moves. Please also see the back and abdominal pages for more muscles that act on the pelvis.
The femur connects to the pelvis at the acetabulum, making up the hip joint. The acetabulum is lined with a tissue called the labrum, which helps to support the hip joint as it moves and supports our body weight.
Fun fact: The hip transmits forces as large as 1.3-5.8 x body weight during walking and 4.5 x body weight during running.
The hip supports the body during static and dynamic movements. Similar to the shoulder, the hip is meant to be very mobile. This means that it also requires support from the surrounding muscles and ligaments to maintain correct alignment of the joint.
The image on the right shows the large amount of ligaments that help keep the pelvis stable.
Even with the large amount of support, the pelvis still allows for some movement.
The motions of the pelvis include:
- Anterior pelvic tilt
- Posterior pelvic tilt
Muscles that act on the hip:
- Quadriceps: rectus femoris, vastus lateralis, vastus medialis, vastus intermedius.
- Hamstrings: semitendinosus, semimembranosus, biceps femoris.
- Gluteals: gluteus maximus, medius and minimus. (There are other muscles in this area that are sometimes grouped with the gluteals when cueing for muscle activation, such as the piriformis, which can be viewed in the images above).
Fun fact: The iliotibial (IT) band is not a muscle. That nasty little thing that runs down the outside of your upper leg is a thick band of connective tissue that connects the tensor fasciae latae muscle to the knee. Even though it is not a muscle, it can still become tight and put an athlete at risk for injury. Runners with poor technique suffer from this quite frequently. Stretching of the IT band is almost impossible because it is so thick, which is why the foam roller is used to help work out any tightness after.
Major muscles surrounding the hip, categorized by function:
- Flexion (think leg goes out straight like in a march): rectus femoris, iliopsoas, tensor fasciae latae and adductor longus.
- Extension (think leg goes straight behind you): gluteus maximus, hamstrings and adductor magnus.
- Abduction (think leg goes out to side): tensor fasciae latae, gluteus medius and gluteus minimus.
- Adduction (think leg comes in from side): adductors (magnus, longus, brevis) and gracilis.
- Internal Rotation (think leg turns inward like someone walking pigeon toed): piriformis, tensor fasciae latae, gluteus medius and minimus.
- External Rotation (think leg turns outward like someone walking like a duck): piriformis, gluteus maximus, medius and minimus.