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In Depth Tutorials and Information
1 
Foot pressure starts at the proximal and lateral aspect of the heel, with
the contact area quickly increasing as load is accepted under the foot
and as the heel plantarflexes.
The position of ground contact is important because it determines how
the forces from the ground act around the ankle and subtalar joints. If
initial contact is made with the ground by the distal part of the heel or
even the midfoot, then the ankle will tend to dorsiflex, not plantarflex. If
the initial contact is on the medial side of the heel, the heel will tend to
invert after heel contact, not evert as is normally the case.
Many describe the foot as behaving as a 'mobile' adaptor in this phase
of gait, because it moves to adapt to the walking surface. In fact, it is no
more mobile in this phase than any other, but it is true that the foot moves
in response to the forces it experiences from the ground and these are
dependent upon the terrain.
Phase 2 of gait
From being only under the heel in phase 1, the load under the foot
spreads to the lateral aspects of the midfoot area and gradually to
the forefoot, too ( Figure 1.6 ). Eventually the heel, mid-, forefoot and
toes are loaded. Thereafter, the upper body is moved from behind to
in front of the foot, and load is progressively reduced under the heel
and increased under the mid- and forefoot. Eventually the heel leaves the
ground.
During this period the tibia has begun to move around the foot and
thus the ankle and entire foot dorsiflexes relative to the leg. Within the
foot, as the mid- and forefoot are progressively loaded, the joints experi-
ence an increased tendency to dorsiflex. These forces are resisted by the
muscles and ligaments on the plantar surface of the foot, including tibialis
posterior and the long flexor muscles. These muscles also assist the
soleus and gastrocnemius muscles in resisting excessive forward motion
of the tibia as the ankle dorsiflexes.
Proximal to the ankle and as the upper body is moved forward of the
foot, the femur and tibia begin to rotate externally. As a result of the
mechanical coupling of the tibia, talus, calcaneus and midtarsal joint, this
external tibial rotation supports supination of the foot, which typically
occurs once the tibia is forward of the ankle. The precise pattern of supi-
nation can vary greatly between people, with some feet supinating from
soon after forefoot loading, and others not supinating until well into the
propulsive phase of gait (phase 3). Supination is further aided by the
action of the posterior leg and plantar foot muscles as they resist dorsi-
flexion within the foot.
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