Biomechanics- Gait

Normal gait is defined as (form of bipedal locomotion) or as a method of locomotion involving the use of the two legs, alternately , to provide both support and propulsion at least one foot being in contact with the ground at all times . It is a series of rhythmic alternating motion of arms, legs, and trunk that create forward motion In order to walk 1- each leg able to support body wt without collapse 2- maintain static and dynamic balance during single leg stance for maintenance of upright posture. 3- sufficient power for limb motion and to advance the trunk. 4- the swing leg able to advance to a position where it can take over the supporting role.

For proper gait 5- proper proprioceptive system 6- normal vision 7- training and experiences Phases of gait cycles The gait cycle begin from heel contact of one foot to the next heel contact of the same foot. During one gait cycle each lower limb has two phases single stance phase and single swing phase

Stance phase From heel contact tell toes off of the same foot (60% of gait cycle) called wt bearing or supporting phase It is subdivided into three intervals 1-initial double stance (10% of cycle of stance) 2-single leg support (40% of cycle of stance) 3-terminal double stance (10% of cycle of stance)

Five sub-phases of stance phase Initial contact or heel strike 2% of gait cycle Loading response or foot flat 2-10% GC Mid-stance body wt over one leg 10-30%GC Terminal stance or heel off 30-50% GC Pre-swing or toe off 50-60% GC

It is subdivided into three sub -phases Swing phase From toe off to just prior to heel strike of the same foot . Called non wt bearing period 40% of GC It is subdivided into three sub -phases 1- initial swing or acceleration from just toe off till maximum knee flexion or the swinging limb is direct under the body 60-73%GC 2- midswing from max. knee flex. Till tibia vertical on ground 73-87% GC

3- terminal swing or deceleration from vertical tibia position to just before heel strike 87-100% GC Increase of gait velocity will decrease gait cycle time and swing time will increase in relation to stance and double leg support & with running no double leg support and there is a float period

Gait analysis Consists of kinematic and kinetic analysis The kinematic analysis includes 1- distance and time variables 2- measurement of joint angles of lower limb and upper limbs 3- determinants of gait

1- Distance and time variables 1- step length 70.5cm(64cm female-73cm male) 2- stride length 3- the width of the base of support 1 to 5 inches 4- degree of toe out about 7 degree

Time variables Step time Stride time Stance time 0.6 sec Swing time 0.4 sec Single limb time Double limb time Cadence: number of steps / unit time. average 113/min Walking velocity : distance/min .average 82m/min

2- measurement of joint angles Lower limb (hip, knee and ankle joints angles in sagittal, frontal and transverse planes) Upper limb (shoulder, elbow and wrist joints angles in sagittal, frontal and transverse planes) Head ,trunk, and pelvic displacement during gait cycle in vertical, lateral and progression.

3- determinants of gait 6 determinants present adjustments made by the body that help to keep the motion of COG to a minimum. 1- first determinant : pelvic rotation in the transverse plane 2- 2nd determinant lateral pelvic tilting in the frontal plane 3- 3rd knee flexion in stance phase

4th and 5th determinants : knee, ankle and foot interaction 6th one : physiologic valgus of the knee . The width between the hips 20-25 cm and the normal step width 8 cm so because the base of support is narrow , little lateral motion of the body is necessary to shift the COG from one Lower Limb to another over the base of support (5-10 degree is the valgus angle of the knee )

Functions 1- the determinants minimize the up and down , and side to side motion of COG to reach only 2 inches 2- they produce a smooth sinusoidal curve of the COG 3- decrease the energy expenditure during normal walking

Kinetic analysis It is the analysis of the forces acting on the body during the gait It includes internal and external forces External forces : like inertia, gravity, and ground reaction force Internal forces : by the muscles which assisted by tendon, ligaments, joint capsules and bony component

External forces The force of gravity acts directly down word through COG of the body at which the body weight is represented by a line . The GRF represents the force of the ground on the foot and it is equal in magnitude and opposite in direction to the force of gravity

From lateral view .it passes via Line of gravity It is an imaginary vertical line which passes perpendicularly in the body and connects between the COG of the segment above by the COG of the segment below From lateral view .it passes via Vertex Mastoid process Atlanto-occipital joint Behind the cervical spine At the junction of cervico-dorsal vertabrae Anterior to the body of the dorsal spine

At the junction of dorso-lumbar vertabrae Posterior to the body of the lumbar vertabrae Anterior to 2nd sacral vertabra Just behind or via the axis of the hip joint Anterior to the axis of the knee joint Anterior to the ankle joint at the level of tarsal bones at about 5- cm

Anterior trunk bending Posterior trunk bending

From front view or back view The vertical LOG passes through the body’s COG which bisects the body into equal halves with the body is equally distributed between the two feet. The location of the LOG relative to the axis of motion of body segment will determined the motion direction .

GRF vector Are forces that act on the body as a result of interaction with the ground and composed of 3 forces . One vertical and two horizontal forces (mediolateral-anteroposterior)

The point of application of GRFV is the body center of pressure(COP ) which located in foot in unilateral stance and between the feet in bilateral standing posture The COP move from psterolateral edge of the heel at heel strike to 2nd and 3rd toes at terminal stance in linear fashion

The pathway of GRFV During stance phase in saggital plane Initial contact: anterior to hip and knee and post. To ankle Loading response : anterior to hip and post. To knee and ankle Midstance : post. To hip and anterior to knee and ankle Terminal stance :post. To hip and anterior to knee and ankle Preswing: post. To hip and knee and anterior to ankle joint

Internal forces They are developed during gait by muscles and the structure which assist the MS by resisting, transmitting and absorbing forces like ligaments, tendons, capsules and bones. The moment created by GRFV is counteracted by muscles activities and other soft tissues

As a principle to identify muscle action and type of contraction put in your consideration If the GRFV passed anterior to joint the posterior muscles will produce counterforce The relation between this forces will determined the desired motion