# Biomechanics Gait PP

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### walking

repetitive activity comprised of multiple gait cycles.

A stride is a
A step occurs between the heel strikes of opposite feet (step length - 72cm and duration - 0.5 sec ).

### gait cycle

occurs between two heel strikes of the same foot. (0% and 100%).

### stride

sequence of events that occur between successive heel strikes of the same foot.

### step

A step occurs between the heel strikes of opposite feet

### step width

lateral distance between heel centers of both sides for two consecutive steps at heel strike

### foot angle

is the angle of in or out-toeing

### Spatial parameters of gait

Stride length, step length, step width, and foot angle are spatial descriptors of gait

defined as the number of steps per minute

### walking speed

distance traveled over a given time
measure of functional capacity often used by clinicians
changes spatio-temporal parameters
While increasing speed, typically, one first maxes out on the step length and then continues to increase cadence

### gait cycle

Each gait cycle consists of two periods of double limb support and two periods of single limb support
0-10%: Double limb support period
10-50%: Right limb is in single limb support (stance phase). At the same time, left limb is in swing phase.
50-60%: Double limb support period
60-100%: Left limb is in single limb support (stance phase) for the last 40% of the gait cycle. At the same time, right limb is in swing phase.

### walk to run

Walking transitions to running at approx. 2 m/sec speed
comprises of single limb support phases only i.e. double limb support phases don't exist in running.

Slow paced walking involve longer periods of double limb support
Application: Marathon walkers always walk so as to minimize the duration of double limb support. They increase speed by increasing step length and cadence.
Conversely, older adults are asked to walk slowly, with shorter steps and less cadence to prevent falls.

### subdivisions of stance phase

Stance phase comprises of heel contact or strike, foot flat, mid stance, heel off, toe off.
Heel off and toe off together are also known as push off.
Heel contact is when the heel strikes the ground (at 0%)
Foot flat is when the plantar surface is on the ground (at 8%).
Mid-stance is when the body's weight passes over the supporting lower extremity (at 30%). It is also when the swing limb just passes over the stance limb. Anatomically, the greater trochanter is right above the mid point of the foot. High hip joint stresses at this point.
Heel off is the instant the heel is off the ground (at 40%)
Toe off is the instant the toes are off the ground (at 60%)

Early/initial swing is from when the foot leaves the ground to when the leg is parallel to the opposite limb (60-75% of the cycle)
Mid swing is from when the leg is parallel to when it is just beyond the supported limb (75-85% of the cycle)
Late/terminal swing is from the mid swing to foot contact with the ground (85-100% of the cycle)

### Center of Mass Displacements

Minimum height at periods of double limb support (5% and 55%)
Max height at periods of single limb support (30 and 80%), is approx 5 cm, and also when supported limb hip joint bears high stresses (30 & 80%).
Medio-lateral displacement is a function of base of support, approx 4 cm, and places high varus/valgus stresses on the knee.

### Kinetic and Potential Energy Considerations

KE is a function of body's speed. PE is a function of body mass, g, height of COM.
In the loading phase (30% & 80%): supporting limb is in front of the body's COM & body is slowing down. KE low, PE high at 30% & 80%.
In the unloading phase, supporting limb is behind the body's COM & body is speeding up. PE low, KE high at 5 & 55%
Cyclic loss and gain of KE and PE minimizes the cost of walking
Gait is most efficient at self-selected normal speed and not at slower or faster speeds

### sagittal joint kinematics of the pelvis and the hip

Insignificant amounts ant/post pelvic tilts.
Hip: In stance, hip flexes 30 at heel contact, and then extends to -10 up to toe off.
In swing, hip flexion of up to 30 achieved until just before heel contact.
Patients with hip joint range restriction rarely show gait deviations because only 30 of flexion and 10 of extn. is needed.
Hip arthrodesis is typically done in 30 F, ER, and neutral abdn.

### Sagital joint kinematics of the knee

5 knee flexion at 0% and continues to flex to 15 up to 10% of the gait cycle-Shock absorption and weight acceptance phase.
Knee extends fully up to 40% or heel off
Knee flexes to about 35 up to 60% or toe off
Max knee flexion of 60 achieved by 75% or early on in mid swing
Knee extends to just short of full extension in mid and terminal swing
Knee motions required for walking are full extension to 60 flexion

### Sagital joint kinematics of the ankle

At heel strike, the ankle is slightly plantar flexed (up to 5)
Ankle plantar flexes into the ground for the first 8% or foot flat.
Ankle dorsiflexes up to 10 as tibia moves on the planted foot (8-30%)
Ankle plantar flexes up to 20 just after toe off
Ankle dorsiflexes to neutral position during swing to clear toes off the ground.
Ankle motion required in gait is 10 of DF and 20 PF.
1st T-MT joint: PF, DF matches that of ankle
1st MTP joint: Slight Hyperextension-Neutral-Hyperextension of up to 55 at toe off

### Frontal Hip Kinematics

Hip: In stance phase, motions are mainly pelvis on femur. In swing, motions are more femur on pelvis.
Heel strike to mid-stance, hip adducts;
Mid-stance to just after toe off it abducts
The majority of the swing phase it adducts.
Knee: Due to high frontal plane stability, little motion occurs.
About 1 valgus in stance and about 5 valgus in initial swing.

### frontal ankle foot kinematics

Little motion occurs at the foot.
Subtalar joint is inverted 2-3 at heel strike
Subtalar and transverse talar joints
Pronation=eversion, abduction
Heel strike to midstance: 3 of eversion occurs.
Midstance to toe off: 6 of inversion occurs.

### horizontal plane hip kinematics

Hip: For majority of stance (0-50%), hip rotates internally
Rotates externally just before toe off & in early and mid swing,
Late swing-IR begins again
6-7 of hip rotations.
In stance, these are pelvis on femur motions and in the swing phase these are femur on pelvis motions.
Max internal rotn. at 50% of gait cycle and max external rotn. in mid swing.

### horizontal knee kinematics

Throughout stance, the tibia internally rotates w.r.t. femur.
At toe off, max int. rotn. of 5
In swing, the tibia externally rotates w.r.t. femur.

### overall horizontal plane motions

Note: Femur rotates more externally than tibia in stance phase. Hence at knee, tibia is always internally rotating w.r.t. femur.
Similarly, femur rotates more internally than tibia in swing phase. Hence at knee, tibia is always externally rotating w.r.t. femur.

### Trunk and upper extremity

Trunk rotations and shoulder girdle excursions of about 7. Helps in increasing the gait efficiency
Shoulder moves reciprocally w.r.t. hip (L sh flexion+R hip flexion)
Shoulder flexion of 10 with 20 of elbow flexion
Shoulder extension of 25 with neutral elbow extension

### Muscle Activation of hip extensors

Phasic activations: Short bursts of electrical activity lasting for 100-400 msec.
Hip extensors: Glut maximus and hamstrings* both are active and acting eccentrically during terminal swing and up to midstance to do a controlled forward fall of the trunk.

### Muscle Activation of hip flexors

Hip flexors: Iliacus, psoas, RF, sartorius become active prior to toe off to decelerate hip extension by acting eccentrically.
Early eccentric activity switches to concentric activity to clear the foot off the ground in initial swing .
Hip flexors are on for the 1st 50% of swing. The other 50% of swing phase is due to flexion from passive forward momentum.
Hip flexors advance the leg forward during swing and lift leg to clear toes.

### Muscle Activation of hip adductors and abductors

Hip Abductors: Gluteus medius, minimus and TFL are active at the end of swing in preparation for heel strike
Together, they are active during the majority of the stance phase.
Prevent dropping of the pelvis on the swing side. In early stance, hip adduction is done by abductor eccentric activity.
After footflat, hip abduction occurs due to concentric activity of hip abductors during the rest of the stance phase.

Hip Adductors work in two phases: a) at heel contact they co-contract with hip flexors & abductors to stabilize the hip b) at toe off they work with hip flexors to flex the hip and clear the foot.

### Muscle Activation of hip internal and external rotation

Hip ERs work eccentrically during early stance (foot flat) to perform controlled int. rotn (gluteus med & min).

At toe off and early swing some sartorius activity is seen. But, most ER occurs passively due to the body's momentum.

After footflat, Hip IRs perform internal rotation due to concentric activity for the majority of the late stance.

### Knee flexors and extensors

Flexors: Hamstrings are active just before heel strike/in terminal swing to just after heel strike to decelerate the knee extension motion in preparation for foot placement.
During initial 10% of stance, hamstrings are active for hip extension and to co-contract and stabilize the knee.

Extensors: Quads activate primarily right after heel strike as they work eccentrically to decelerate the knee flexion as the foot flattens on the ground.
Quads also act concentrically to extend the knee and stabilize it during mid stance.

### Ankle foot muscles

Ankle Dorsiflexors (Tib Ant):
Eccentric activity for controlled plantar flexion, eversion towards the ground during early stance.
EHL, EDL:
Work eccentrically with Tib Ant in early stance.
EHL, EDL also work in swing to keep the toes extended and off the ground.
Tib Post:
Eccentric activity prevents excess pronation in early stance
Concentric activity supinates the foot in late stance.
Ankle PF:
From footflat to just before heel off, soleus and gastrocs act eccentrically to do a controlled dorsiflexion as the tibia moves forward on the fixed foot.
They also help in plantar flexion during push off.
Peronei: Active in 20%-60% as plantar flexors and as stabilizers of the ankle to prevent excess inversion by tib. post.
Intrinsic muscles of foot: Active during mid stance to toe off (30-60%). Stabilize the forefoot and maintain the medial arch in terminal stance.

### Trunk

Back extensors: 0-20% and 45-70% for controlled forward movement of the trunk at each heel strike and push off.
Rectus Abdominis: 20% and 70% corresponds with hip flexor activity to stabilize the pelvis and lumbar spine.

### Gait Kinetics and Ground Reaction Forces

Resultant GRF exerted are represented in a butterfly pattern during each step
Vertical peak value is 120% of BW
Ant-post peak value is 20% of BW
Medio-lateral peak values are 5% of BW
Relevance: Vertical GRFs during walking exert high stresses on your lower limb and spine during walking. In acute back or lower-limb pain, complete bed rest is recommended.

### Gait Pathology

Antalgic gait in a patient with painful knee/ankle: Decreased % stance on painful limb (i.e. step length and stance time) and swing time on opposite side.

Parkinsonian gait (Shuffling gait): Trunk, hip, knee flexion and shuffling gait. Short steps and higher cadence. Lack of associated movements of arms, and lack of trunk rotation

Ataxic gait: Broad base of support, ataxic tremors.

CP gait: Ant. pelvic tilt, hip flexion, adduction, internal rotn. with knee flexion, and ankle plantar flexion, foot inversion.

### Hip Muscle Weaknesses

Extensor lurch: Trunk hyperextension in stance

Abductor lurch: Trunk lateral flexion in stance

Circumduction gait e.g. hemiplegia. Circumduction in swing for foot clearance

Hip hiking: Hip hiking in swing for foot clearance e.g. in hemiplegia
Other impairments in hemiplegia: Lack of arm movts, trunk rotations, other phases of gait may be affected depending on severity

### Knee Muscle Weakness

Knee hyperextension in stance e.g. quads/gastrocs spasticity or paralysis

Lack of knee flexion in swing may be associated with hip circumduction/hip hiking in swing. Due to hamstring paralysis or quads spasticity.

Unilateral knee flexion contracture: leg length discrepancy-ankle plantarflexion on the affected side to equalize the limb length.

Bilateral knee flexion contractures lead to increased dorsiflexion position to keep the feet flat on the ground
They also lead to shorter leg lengths and no heel strike.
Stance limb will crouch (flex at hip, knee, and ankle) and the swing limb will need greater flexion at hip and knee.
Excess motions may be needed at the trunk. Knee extensor activity will be high increasing metabolic demands of gait.

### Ankle Muscle Weakness

Foot drop gait/high steppage due to paralysis of dorsiflexors, foot slaps on the ground in stance, no heel strike, increased hip knee flexion to clear the foot off the ground or vaulting of the opposite limb in the swing phase.

Plantar flexor tightness/spasticity (e.g. pes equinus) or heel pain: No heel strike. Secondary knee hyperextension and increased vertical excursion of the body's COM may also be seen with increased plantar flexion.

Similarly, in ankle arthrodesis (neutral ankle). Heel strike is possible but plantar flexion is not possible. So push off is ineffective.

### Quiz Questions

Which motions occur at the hip, knee, and ankle during the first 20-30% of the gait cycle also known as shock absorption or loading phase.

Trunk/Pelvis/Hip (Pelvis on femur): Undergoes a controlled forward lean, flexion, adduction, internal rotation

Knee: flexion

Ankle: plantar flexion, eversion

### Which muscles are active during the first 20-30% of gait cycle and how (eccentrically/concentrically)?

Trunk/Pelvis/Hip (Pelvis on femur): ecc hip extensors, ecc abductors, ecc external rotators

Ankle: ecc dorsiflexors, ecc invertors

### Which motions occur at the hip, knee, and ankle during the first 30-60% of the gait cycle also known as unloading phase.

Trunk/Pelvis/Hip (Pelvis on femur): extension, abduction, internal rotation

Knee: extension--followed by flexion

Ankle: dorsiflexion--plantar flexion, inversion

### Which muscles are active during the 30-60% of gait cycle and how (eccentrically/concentrically)?

Trunk/Pelvis/Hip (Pelvis on femur): ecc hip flexors active just before toe off, conc abductors, conc internal rotators

Ankle: ecc. plantarflexors - conc. plantar flexors, conc. invertors

### Which motions occur at the hip, knee, and ankle during the swing phase of the gait cycle?

Trunk/Pelvis/Hip (Pelvis on femur): flexion, slight adduction, slight external rotation followed by slight internal rotation to be neutral at heel strike

Knee: flexion and at terminal swing knee extension

Ankle: dorsiflexion - stays neutral, neutral in other planes

### Which muscles are active during the swing phase of gait cycle and how (eccentrically/concentrically)?

Trunk/Pelvis/Hip (Pelvis on femur): conc hip flexors in the first 50% of swing

Knee: not early on - in terminal swing ecc hamstrings

Ankle: static dorsiflexors

Example: