In this part of the glutes series, I will detail the functions of the gluteus maximus, gluteus medius and gluteus minimus. First, understand that every muscle must load in all three planes of motion before they can unload with maximal force. The glutes are no different in this regard, although one of the principle roles of the glutes are to eccentrically decelerate the forces generated by gravity, momentum and ground reaction forces.
Let's look at the functions of the gluteus maximus, gluteus medius and gluteus minimus:
1. First, the gluteus maximus is the largest muscle in the body (Wow!). It originates at the ilium (posterior crest), sacrum (posterior) and lumbar fascia. It inserts into the femur (gluteal line, or rear) and tibia (lateral condyle). The primary function of the gluteus maximus is to extend the hip (moving the thigh to the rear). A summary of the gluteus maximus' muscle contractions are:
Concentric (force production) - Accelerates hip extension and external rotation
Eccentric (force reduction) - decelerates hip flexion and internal rotation
2. The primary role of the gluteus medius and gluteus minimus is to abduct the hip. Abduction separates your legs away from the midline of the body. The minimus lies underneath the medius. They both originate at the ilium and insert into the femur (greater trochanter, or side). Abduction occurs during any athletic movement requiring you to move from side to side such as playing the infield in baseball, defense in basketball and football, and ice skating. The gluteus medius and gluteus minimus also have critical roles in gait (walking) because they stabilize the pelvis. This prevents the pelvis from tilting sideways when you are balancing on one foot. A summary of the gluteus medius' and gluteus minimus' muscle contractions are:
Concentric (force production) - accelerates hip abduction and internal rotation
Isometric (stabilizes force) - stabilizes the lumbo-pelvic-hip complex
Eccentric (force reduction) - decelerates hip adduction and internal rotation
The gluteus maximus, gluteus medius and gluteus minimus are sometimes called the "gluteal deltoid" because together they form the same shape as the deltoid muscles of the shoulder. The gluteal deltoid also performs similarly to the shoulder's deltoids. The deltoids move the shoulder through all planes and the gluteal deltoid does the same for the lower extremities.
In part 4 of the glutes series, I will look at exercises that primarily strengthen the gluteus maximus, gluteus medius and gluteus minimus.