1. Biomechanics- Gait

2. 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.

3. 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

4. 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)

5. 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

6. 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

7. 3- terminal swing or deceleration from vertical tibia position to just before heel strike % 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

8. 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

9. 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

10. 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

11. 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.

12. 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

13. 4th and 5th determinants : knee, ankle and foot interaction
6th one : physiologic valgus of the knee . The width between the hips 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 )

14. 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

15. 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

16. 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

17. 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

18. 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

19. Anterior trunk bending Posterior trunk bending

20. 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 .

22. 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)

23. 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

24. 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

25. 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

26. 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