Abstract Gait analysis offers a unique means to measure the mechanical factors of joint loading, orientation, and neuromuscular function during activities of daily living such as walking. Walking is a cyclic process; therefore, the relevant information can be captured during one complete gait cycle, which is the time between successive foot contacts of the same limb.
A Typical Gait Cycle the duration that occurs from the time when the heel of one leg strikes the ground to the time at which the same leg contacts the ground again 2 phases stance phase (62%) swing phase (38%) A typical gait cycle lasts 1-2 sec, depending on speed.
Anatomy Before discussing the specifics of gait lets take a quick look at the bones involved. The key boney structures are the talus (2) and calcaneus (1), located at the ankle. The three part joint formed by these two bones is called the subtalar joint. Other key bones include the navicular (3)and cuboid (7), located just anterior to these bones. The two individual joints formed by the talus and navicular and the calcaneus and cuboid make up what is known as the mid-tarsal joint. The leg bones of significance include the femur which is the thigh bone and the tibia which is the larger of the two lower leg bones. The fibula is the smaller leg bone. In front of the tibia is the patella or knee cap. We will not review the anatomy in detail.
Stance Phase (Support Phase) the duration when the foot in contact with the ground the duration from heel strike to toe off 3 subphases :initial contact period from heel strike to foot flat,midstance period from foot flat to heel off,propulsive period from heel off to toe off.
Swing Phase (Recovery Phase) the duration when the foot in the air the duration from toe off to heel strike 3 subphases : acceleration midswing deceleration
Force Flow Force flow through the foot may be measured today by a variety of means. The Electrodynogram was the first system available for office use and consisted of 7 sensors applied in standard positions on the foot. Other technology accomplishing this exists today. This technology that gives us the advantage to observe forces beneath the foot which we can not visually see.
Force Flow It also measures the timing of the phases and subphases of gait that we have reviewed and greatly increases our knowledge of what is occurring during the gait cycle. Normal pressure flow through the foot starts slightly lateral in the heel and flows forward to between the first and second metarsal and exits throught the great toe.
Resolution of forces When we walk, we also produce friction forces on the ground. For example, when the foot hits the ground at heel strike, the friction between the heel and the ground causes a horizontal force to act backwards against the foot.
What will be the effect of this force on the body? Remember Newton's equation, F = m.a? It also works for horizontal, friction forces as well as for vertical, load forces. The equation tells us that if there is a backwards force on the body, there must also be a backwards acceleration. The force therefore causes a braking action on the body, slowing it downNewton
Here, the force is tilted over forwards, causing a forwards acceleration on the body, speeding it up into the swing phase. Notice that the ground reaction force is not completely horizontal - it's tail is still in the air, so there must still be some vertical, load force. In fact, it's very rare to have only a vertical or a horizontal force on the body - usually they both act together as what's known as a ground reaction vector (GRV). We can see how much of each is present at any time by drawing a triangle:
The size of the friction force is represented by the length of the horizontal line (base of the triangle), while the size of the load force is indicated by the length of the vertical line (height of the triangle). The hypotenuse of the triangle is known as the resultant force.
The Ground Reaction Vector in Normal Gait We've seen that the GRV is tilted backwards at heel-strike, and forwards at toe-off. What does it do between these times? A plot of the GRV through the gait cycle is called a butterfly diagram because the pattern made resembles the wings of a butterfly!
We can see that the vector swings round from backwards at heel-strike, vertically during the middle of stance, then forwards at toe-off. Notice that it's height changes, too. It's very small at heel-strike, rises to a maximum soon afterwards, then falls a little during the middle of stance, rises again, then falls before toe-off. This must mean that the vertical reaction force on the body also shows this pattern:
The friction force, as we saw, acts backwards (negative) after heel-strike and forwards (positive) towards toe-off. It changes at some time during the middle of stance - about 36% of the cycle. Notice the scale on the vertical (y) axis.