Muscles of the racehorse: hindquarters
1: Gluteus medius
The gluteus medius, together with the biceps femoris (see Figure 2), generates the power to propel the body forwards. This muscle has an extension, the ‘gluteal tongue’, which feeds into the longissimus muscle.
2: Quadriceps femoris
The quadriceps femoris consists of four individual muscles. The horse uses these muscles to bring its hocks underneath its body.
As its name suggests, the longissimus is the longest muscle in the body. It starts in the pelvis and runs forward all the way to the horse’s skull. Its main function is to stabilise the horse’s spine as it runs.
1: Biceps femoris
These two muscles extend the hip, stifle and hock. When the hind leg is planted on the ground, they push the body forwards.
The power generated by the hindquarter muscles is transferred forward via the sacroiliac joint, deep in the pelvis.
Note the muscle definition between (1) the quadriceps and the biceps femoris and (2) the biceps femoris and semitendinosus.