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The gait of the Homo sapiens is a distinctive process, which differs in its mechanics from the four-legged gait of other species. Due to repeated pattern in gait, it can be described as a cycle. Therefore, gait cycle can be defined as a particular pattern starting from one foot contacting the ground, and ending when the same foot contacts the ground again (Metzger). The cycle is comprised of two main phases, which are the stance phase, i.e. when the foot is in contact with the ground and bearing weight (60 to 65 percent of the gait cycle), and swing phase, i.e. the phase from the toes detached from the ground to the same foot contacting the ground (35 to 40 percent of the gait cycle). In the swing phase the foot in motion and not bearing any weight.
An important aspect of gait is the shock absorption process during gait, which is achieved through the distribution of the load between the forefoot and the rear foot.
As the foot during the swing phase bears no weight, the distribution of loads occurs only through the stance phase. In that regard, the stance phase can be divided into four main instances, representing the foot positions, which are (Magee 941):
- Heel strike
- Load response (foot flat)
- Single-leg stance
- Heel off
- Toe off
At heel strike, the first task occurring is shock absorption, which is lessening the impact of body weight dropping onto supporting foot (Perry 73). Hence, the load is initially imposed on the talus, causing the first of the absorption mechanisms, i.e. subtalar eversion (the eversion of the joint between the talus and the calcaneus). With the rest of the feet moving toward ground contact the support of the calcaneus for the talus is reduced.
Load response (foot flat)
The shock absorption continues toward the foot flat, where the fore foot is in pronation, unlocking the subtalar and metatarsal joints for the shocks to be absorbed more effectively.
At the onset of single-leg stance (middle stance), the shock absorption mechanism following the subtalar eversion is the midtarsal dorsiflexion, which contributes to the shock absorption. Additionally, another load distributing function occurs at this stance, which is weight-bearing stability. The demand for the mid foot stability is at its peak, when the total weight is on a single foot. In that regard, to increase the stability of the mid foot, the midtarsal joint reverses the everted position into an inversion, while midtarsal joints lock along with all inverting muscles (soleus, tibialis, posterior, flexor, digitorum longus and flexor hallucis longus) increasing their intensity, providing the added support (Perry 76). The demand for stability gradually increases until it is on its peak, with the rise of the heel.
With the heel off stance, the body weight is gradually transferred fully onto the forefoot. The support area increases with the addition of proximal phalangeal base to metatarsal head. The metatarsal support is mainly the result of the action of peroneus longus on the first metatarsal. Plantar flexor muscles begin to contract to prepare for the push off.
The toe-off stance marks the last area of the forefoot in contact with the ground, which is the first metatarsal, as body weight shifts toward the other foot. The foot is in supination, with the plantar flexor muscles at peak, becoming inactive as the foot leaves the ground (Magee 949).
Magee, David J. Orthopedic Physical Assessment. 4th ed. Philadelphia: Saunders, 2002. Print.
Metzger, Sherry. “Making the Most of Movement: Gait Analysis and Bracing”. 2007. O&P EDGE. Web.
Perry, Jacquelin. Gait Analysis: Normal and Pathological Function. Thorofare, NJ: SLACK, 1992. Print.