What is gait
cycle exactly? A gait cycle is a series of events in walking or running, and it is measured from one foot
contacts the ground (heel-strike) and to the
same foot contacts the ground again. 

Gait cycle has
two phases: the weight bearing or stance phase
and the non-weight bearing or swing phase.

Each gait cycle begins with an initial contact – or heel-strike – of the
leading leg in the stance phase, goes through a swing phase then ends with the
next contact of the ground with the same leg. 

Stance
phase:  stance phase takes up about 60% of the gait cycle. In this
phase the foot is on the ground, and that foot
accepts body weight and provides single leg support. It can be subdivided into initial
contact (or heel-strike), loading
response, mid-stance, terminal
stance and pre-swing.

– initial
contact – or heel strike – occur when the heel of the
leading leg contacts the ground. It absorbs shock and stabilises the new
position. Hip extends, quads and tibialis anterior contract eccentrically.

After heel strike the body weight is being transferred to the
leading limb.

– loading
response – initial double limb stance: occur after the initial
contact of the leading leg onto the ground, the foot moves from the heel to the
toe making the entire foot in full contact with the ground, the bodyweight
is being transferred onto the stance limb, until the opposite limb is elevated.

Tibialis anterior and quads contract eccentrically. 

– in mid-stance –
single limb support. The limb is fixed and weight is shifted onto this
limb – called single legged stance – and the foot turns into stability
mode supporting the opposite
limb freely swinging forward till both ankles of the limbs are aligned.

Hip extensors and quads contract concentrically.  

– in terminal
stance – single limb support – begins when the supporting heel
raise off the ground and ends when
the contralateral heel
touches the ground. Weight moves ahead of the forefoot, the ankle starts
to flex downward and the knee extends and the body is propelling forwards.

Pre-swing: is the terminal
double-limb support period. It starts when the contralateral heel touches the ground and ends when the ipsilateral limb is elevated.

Hip flexors contract.

Swing
phase: takes up about 40% of the gait cycle. In this phase the foot is off
the ground and moving
forward. In this phase the limb advances. It can be subdivided
into Initial swing, Mid-swing and Terminal
swing. 

Initial swing:
– toe off. It
begins when the foot leaves the ground till full knee flexion occurs,
the swinging limb is positioned directly under the body and directly
opposite the stance limb. 

mid-swing: it begins right after knee flexion and ends when the
tibia is in a vertical position. Tibialis anterior,extensor hallicus longus, extensor digitorum longus, and peroneus teritus contract. 

Terminal
(late) swing: it begins when the
tibia passes beyond plumb, the hip flexes (about 30 degrees), the knee
fully extends and the ankle is neutral – all preparing the heel to contact the
ground.