Figure 11.2 shows the left fore lift-off from the ground. As the horse is on the right lead this is called the non-lead fore lift-off. The horse has only the right fore on the ground and is said to be in lead fore single stance. The horse’s body is launched off the ground by a powerful thrust of the leading forelimb, marking the end of fore lead single stance and the start of the airborne phase in gathered suspension.
Figure 11.5 shows the airborne phase of the stride with the horse in gathered suspension. In a galloping horse the forelimbs are just as responsible for propulsion as the hindquarters. The suspension phase allows the horse to:
- Recover its equilibrium – in lead fore single stance (Fig. 11.2) the horse’s centre of gravity has shifted forwards and the viscera have pressed against the lungs, forcing the horse to breathe out. The horse needs to move the centre of gravity back again to be able to inhale. Respiration rates can reach 180 breaths per minute.
- Get its hind feet underneath the body – the combination of body weight and a rigid spine mean that if a foreleg was on the ground the horse would not be able to bring the hind limbs sufficiently underneath the body. This contrasts with the greyhound, which has a flexible spine, which enables it to get its hind limbs right under its body.
In the gallop the spine can be flexed slightly to bring the hind limbs forward at the beginning of the stride. The croup is flexed (Fig. 11.6) around the lumbosacral joint by contraction of the hip flexors (psoas major and iliacus) and relaxation of the longissimus dorsi and middle gluteal muscles. Sideways movement of the spine is minimised by the iliocostalis, longissimus, spinalis and multifidus muscles.
In Fig. 11.8 the non-lead (left) hind is about to hit the ground. During this phase it is the only foot on the ground so this is known as the non-lead hind single stance.