Swimming Anatomy

The gluteal group contains the three gluteal muscles and a collection of six deep rotators. The gluteus maximus (figure 7.2), the largest and most superficial of the gluteal muscles, arises from the posterior half of the pelvis and a portion of an adjacent bone called the sacrum. It then crosses the hip joint to combine with the IT band, also attaching to a small portion of the femur. The main action of the gluteus maximus is extension of the hip. It also assists other muscles in the region with external rotation of the hip. The gluteus medius and minimus both lie deep to the gluteus maximus and arise from the lateral part of the pelvis. The two muscles cross the hip joint, attaching to a bony prominence on the femur called the greater trochanter. Both muscles function to abduct and internally rotate the hip. The deep rotators are a collection of six small muscles (piriformis, gemellus superior, gemellus inferior, obturator externus, obturator internus, and quadratus femoris) that combine to rotate the hip externally and, like the rotator cuff at the shoulder, stabilize the hip joint.

Figure 7.2 Muscles of the back of the legs.

The posterior group is composed of the three hamstring muscles. The biceps femoris, as the name implies, has two heads, one arising from a part of the pelvis called the ischial tuberosity and the other arising from the lower posterior aspect of the femur. The two heads combine to form a common tendon that inserts on the head of the fibula. The other two hamstring muscles, the semitendinosus and semimembranosus, also originate from the ischial tuberosity but run along the medial aspect of the knee joint to attach at the medial surface of the superior part of the tibia. Collectively, the muscles extend the hip and flex the knee.

The muscles of the lower leg can be grouped according to their actions at the ankle joint. The gastrocnemius and soleus are the primary plantarflexors and share an insertion into the Achilles tendon. The tibialis anterior and posterior, named according to their attachment location on the tibia, function to invert the foot. The fibularis muscle group (fibularis tertius, fibularis brevis, and fibularis longus), located on the lateral aspect of the ankle joint, originates from the fibula and has the primary function of foot eversion.

For discussion purposes, the muscle recruitment patterns of the freestyle and backstroke flutter kick are described jointly because the patterns are practically identical. The propulsive portion of the flutter kick begins with the torso and core-stabilizing musculature acting as the foundation on which your legs generate their force. The actual kicking movements begin with the hips in a small amount of extension. From this extended position the iliopsoas and rectus femoris are activated to initiate hip flexion. Also acting on the knee joint, the rectus femoris initiates knee extension and is quickly joined by the remainder of the quadriceps group, which helps to increase the force produced during the kick. These muscles remain active throughout the entire propulsive phase of the kick. At the ankle joint, the tibialis anterior and tibialis posterior work in concert to maintain the foot in a position of slight inversion, while contraction of the gastrocnemius and soleus plantarflexes the foot. The hip extension that takes place during the recovery phase is guided by the hamstrings and gluteus maximus. Unlike in flutter kicking, during butterfly and dolphin kicking the torso serves not only as the foundation for the kick but also as a component. The undulating body movements of the torso initiate the kick, and paired movements of the legs follow in a manner identical to the action of the flutter kick. One difference in the paired movement of the legs is that a greater amount of flexion and extension occurs at both the hips and knees. The undulating movement of the torso is guided by the contraction of the abdominal and erector spinae muscles, but the muscles that guide the movements of the legs are identical to those used in the flutter kick.