Normal and Pathological Gait Flashcards
Define Gait
the manner or style of locomotion involving the use of two legs, alternatively, to provide support and propulsion, while at least one foot being in contact with the ground at all times.
Important aspects of gait - definition info
During gait you are always in double or single support (one leg is in contact with ground at all times) (running = one foot off the ground)
normal gait has general characteristics but is specific to how you walk (unique)
two purposes of the legs during gait
- prevent collapse
2. propel yourself in the direction of motion
What is the purpose of gait?
to transport the body safely and efficiently across the ground (from point a to point b)
efficiency is key! walking for exercise = goal to walk to burn calories; not efficient
Purpose of gait on different surfaces
level: how much mass is transported how far? (mass x distance = work)
Uphill/downhill: consider change of altitude, PE = mgh
uneven terrain: safety (NM control, prevent from collapse, balance of upper body, foot trajectory clearance)
5 Major motor functions during gait
- Support of upper body
- Dynamic balance
- Foot trajectory control
- Generation of mechanical energy
- Absorb mechanical energy
Support of upper body
prevent collapse of lower limb during stance
upper body needs to be controlled so visual and vestibular systems can work during gait
Dynamic balance
maintenance of upright posture and balance of the entire body
important because sensory information can override locomotive system
Foot trajectory control
to achieve safe ground clearance and gentle toe or heel landing (toe off to heel contact)
generation of mechanical energy
maintain or increase forward velocity
mechanical energy required for every step of gait
generating energy = concentric contraction
absorb mechanical energy
shock absorption and stability or to decrease forward velocity of the body (occurs at every joint, especially the knee)
absorbing energy = eccentric contraction
Spatial and temporal descriptors on level walking include what two things?
time and distance parameters
Time parameters of walking on level ground
stance time = 0.5 seconds single support time double support time swing time stride or step time
Double support
22% of gait cycle total
decreases when speed of walking increases
increases in elderly or those with balance issues
0 time spent in double support while running
stride vs step time
stride time is not very useful
step time is important! It will decrease on the affected side (limping)
Distance parameters of walking on level ground
stride length
step length
step width
degree of toe-out
Stride length
decreases in elderly
increases as speed of walking increases
step width
increases in those with balance issues
medial lateral direction
Rate (distance/time) variables
cadence: steps per min
walking/gait velocity: distance/unit of time
Cadence
comfortable speed = 80-110 steps/min
fast = 120 steps/min
40-55 strides/min = 80-110 steps/min
1 stride = 2 steps
Can two people walk at the same speed and have different cadences?
yes: kid walking with parents
kid has much higher cadence than parent
parent has larger stride length
cadence and stride length contribute to speed
pathologies cause decreased stride length
Walking/gait velocity
(0.9 - 1.7 m/s)
increases w/ increased cadence and stride length simultaneously
decreases w/ decreased angle of toe out and limb length or weight
increased speed = decreased duration of all stance phase components (sub phases)
avg walking gait/velocity = 1.3 m/s
walking at 1 m/s = slow
Other kinematic variables
center of mass position and velocity during gait
linear position, velocity and acceleration of the COM, pelvis, and head during gait
linear position and velocity of the toe during gait
angle change of each joint during gait
Displacement of COM in vertical and lateral directions
vertical displacement of COM = 5cm
lateral displacement of COM = 4cm
Vertical displacement of COM
30% of gait cycle (end of midstance) is the highest point of trajectory
55% of gait cycle (middle of double support) is the lowest point of trajectory (preswing)
at the same time of the highest trajectory = COM is closest to the foot that is in contact with the ground
Energy cost of gait
- muscles affect the rate of energy expenditure during gait
- the overall metabolic cost of walking can be assessed by measuring O2 consumption and CO2 production
- Oxygen rate at average walking speed is 80 m/min or 1.3 m/s or 3 miles per hour. or 12 ml/kg/min (energy cost of walking)
how do muscles affect the rate of energy expenditure during gait?
increase/decrease speed of motion lift body against gravity decelerate different body segments stabilize joints so they don't move (co-contraction) lower BW
Compass vs normal gait
normal gait is more efficient than compass gait because vertical excursion is much smaller
Purpose of 6 determinants of gait
minimize COM movement, therefore minimizing energy consumption
6 determinants of gait
- pelvic rotation about the vertical axis
- pelvic tilt about AP axis
- knee flexion in stance phase
- ankle mechanism
- foot mechanism
- lateral displacement of body
Pelvic rotation
pelvic rotation decreases COM vertical displacement anteriorly at heelstrike and posteriorly at toe-off
Pelvic tilt
decreases COM vertical displacement
Knee flexion
decreases COM vertical displacement
foot/ankle mechanism
decreases COM vertical displacement during stance
Lateral displacement of body
normal leg = valgus, meaning knee joint centers closer than hip joint centers, allowing me to put feet closer together, meaning my COM does not displace/move as far in M/L direction during gait
Toe kinematics
max toe clearance is 1.3 cm (??)
max horizontal velocity of foot during walking is 4.6 m/s (??)
fast velocity of foot during swing with little toe clearance = high trip/fall risk
lowest toe clearance occurs at max horizontal velocity of the foot!!!!
What happens to the head and pelvis M/L acceleration with age?
although acceleration in ml direciton of pelvis decreases slightly, the head motion increases and is more than the pelvis. head motion should be smaller than pelvic!
what happens to step width with age?
step width increases – wider BOS – safety mechanism – more stability
Kinetic variables
(causes of motion) GRF center of pressure joint moment (torque) joint power
Foot kinematics at heel strike
vertical GRF = “M pattern/shape” of graph
spike in graph at IC = Heelstrike Transient
Heelstrike transient
abnormal spike in graph at IC
coordination issue with IC of heel on ground, landing should be smooth. Knee is still in screwhome mechanism, so force from hitting ground will be transferred to knee
Forces that control walking
gravity (BW)
air resistance
internal muscles forces
GRF
GRF
normal component = vertical forces
shear component = AP and ML friction forces
direction of GRF changes during gait
Vertical GRF
double peaks:
1st at heel strike (action of body momentum)
2nd peak at push off - contraction of calf muscle
these peaks are higher than BW because you are creating more force
IC = creating more force from ground. force is greater than BW to prevent COM from dropping
peak value of vertical GRF
120% BW at peaks (push off and heel strike)
When is the vertical GRF lower than your BW?
midstance - result of knee flexion
AP GRF component
magnitude and direction of AP shear force depends on position of COM relative to location of foot
peak value = 20% BW
sufficient friction force btwn foot and ground is needed to prevent slipping
propulsive force of one limb is applied simultaneously to the braking force of the other limb when the weight is transferred from one limb to the other
AP GRF
magnitude and direction of AP shear force depends on position of COM relative to foot location:
- in the posterior direction at heel strike for slowing the progression of the body
- in the anterior direction at toe off for propelling body forward
- larger the step length = greater shear forces
AP GRF during push off
during push off, tendency of motion is for foot to go backwards but friction applies force forwards (prevents slipping)
1st step = high positive on graph because you are gaining speed
to slow down you have to create more negative force than positive
The magnitude of the ML shear force depends on the position of the COM relative to the foot:
lateral direction at heel strike
medial direction during rest of stance phase
larger step width = greater shear forces b/c of greater angle btwn LE and floor
peak value = 5% BW
wide variety depending on foot type
peak value will increase if BOS increases
medial force from ground helps transfer weight to opposite side during gait
ML = friction force
Trajectory of COP during gait
at heel strike, COP is located lateral to midpoint of heel
mid stance, COP moves more laterally
from HO to TO, COP moves medially from MT heads to big toe
pronated foot = COP shifted over medially
COP at LR
heel
COP at mid stance
heel and midfoot
COP at terminal stance
forefoot only
COP at pre swing
medial forefoot
Joint Moment at heel strike
at heel strike, the line of action of the GRF passes post to ankle joint, post to knee joint, and anterior to hip = ankle PF, knee flexion, hip flexion torques
to prevent collapse of LE, these external torques are counterbalanced by internal joint moments that are created by ankle DF’s, knee extensors, and hip extensors
Internal moments do not: (2 things)
- do not indication the direction of motion
- do not indicate co-contraction of agonists and antagonists
a muscle being active doesn’t mean the joint will move in that direction of contraction
Joint moment notes
at IC we have PF torque, but TA is active
at knee = external flexion torque, but quads are active
muscles create internal torques/moments to counter GRFs
GRFs create external torques on joints
Torque + motion = ?
joint power
Definition of joint power
the rate of work performed by controlling muscles
the product of the net joint moment and the joint angular velocity
significance of joint power
indicating the net rate of generating or absorbing energy by all muscles and other connective tissues crossing the joint
- positive value = power generation = concentric contraction
- negative value = power absorption = eccentric
motion and torque can be in the same or opposite directions
First rocker occurs when during the gait cycle?
IC thru LR
first rocker fulcrum
fulcrum = heel - DF moment
PF controlled by DF muscles to counter balance the PF torque of GRF
second rocker occurs when?
mid stance
fulcrum of second rocker?
fulcrum = ankle - PF moment
DF controlled by PF muscles to counter balance DF torque of GRF
rotation around ankle joint (fulcrum)
third rocker occurs when?
terminal stance
third rocker fulcrum
fulcrum = MT heads - PF moment
PF produced by PF muscles
heel rotates around MT heads
occurs from RHO to LIC
Limitations of Kinematic data
kinematics can mislead w/ respect to determining how motion is coordinated by the muscles groups that created the motion (sprinter example)
Hip joint power peak at mid stance
extensor generation of power during mid stance
hip joint power peak at terminal stance
flexor absorption of power
hip joint power peak pre swing
flexor generation of power during pre swing
hip joint power peak loading response
abductor absorption of power during loading response
Knee joint power peak LR
extensor absorption of power during LR
knee joint power peak pre swing
extensor absorption of power during pre swing
Ankle power peak LR
DF absorption of power during LR
ankle power peak terminal stance
PF absorption of power during terminal stance
ankle power peak pre swing
PF generation of power during pre swing
