Biomechanics 1+2

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Gait Introduction Ambulation or locomotion. Consists of 1 stride 2 phases , and 8 events. Is a translatory progression of the body as a whole produced by a coordination rotary movements of body segments.

Movements of body segments The translatory progression is rhythmic and characterized by alternating propulsive and retropulsive motions of the lower extremities. During gait the lower extremities support, balance, carry, and transfer the head, arms, and trunk (HAT) which constitute 75% of the body weight, the head and arm 25% and the trunk 50%. Tasks accomplished with each gait cycle . • Acceptance and balance of HAT. • Transfer HAT from one extremity to another. • Lift 1 extremity of the ground and place in front of the other in alternating pattern.

Neuromuscular component of gait 1. Activation of gait neuromuscular in central nervous system. 2. Transmission of neural commands to the peripheral system. 3. Muscular contraction and producing movement. 4. Generation of forces and moment at the joints. 5. Regeneration of the joint forces and moments. 6. Linear and angular displacement of the bodies segments. 7. Generation of ground reaction forces.

Gait Cycle During bi-pedal locomotion, there are 2 distance phases:

Stance phase ( 60-62% ): contact phase

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Begins with 1 extremity contacts the ground ( Heel strike), and ends as the feet is leaving the ground (Toe off) and consists of 5 events:

Traditional

RLA

Heel strike

Initial contact

Foot flat

Loading response

Mid stance

Mid-stance

Heel off

Terminal stance

Toe off

Pre swing

Swing phase (38- 40%): no contact phase Begins with as soon as the toe of one extremity leaves the ground and ceases just prior to heel strike or contact of the same extremity when the feet swings toward the next stance phase, and consists of 3 events:

Traditional

RLA

Acceleration

Initial swing

Mid-swing

Mid swing

Deceleration

Terminal swing

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Stance phase Heel strike or Initial contact -

The moment when the red foot just touches the floor.

- Normally the heel is the first part of the foot to touch the ground. -

Beginning of the 1st double support.

- Mean while, the blue leg is at the end terminal stance.

Foot flat or loading response -

0 to 12 percent of the gait cycle.

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The double stance period beginning with the foot contacting the floor until the other foot is lifted for swing.

- Body weight is transferred on to the red leg. - Meanwhile the blue leg is the pre-swings phase.

Mid-stance or mid stance -

Single limb support during which one limb must support the entire body weight and provide tranquil stability while progression must be continued.

Heel off or terminal stance

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Begins when the red heel rises and continues until the heel of the blue foot hits the ground.

-

Body weight progresses beyond the red foot as increased hip extension puts the leg in a more trailing position.

Toe off or pre swing -

The 2nd double support stance interval in the gait cycle.

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It begins with the initial contact of the blue foot and ends with red toe off.

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Ground contact by the blue leg causes the red leg to increase ankle planter flexion, knee flexion, and decrease hip extensor.

Swing phase Acceleration or Initial swings -

Begins when the foot is lifted from the floor and ends when the swinging foot is opposite the stance foot.

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The red leg is advanced by increased hip and knee flexion.

-

The ankle only partially planter flexion to natural to ensure ground clearance.

-

It is during this phase that a foot drop gait is most appearant.

- The blue leg is in mid stance.

Mid swing or mid- swing - Continues from the end point of the initial swing and continues until the swinging limb is in front of the body and the tibia is vertical. - Advancement of the red leg is accomplished by further hip flexion. -

The ankle is allowed to extend in response to gravity while the ankle continues dorsiflexion to neutral.

-

The blue leg is in late mid- stance.

Deceleration or terminal swing - Begins when the tibia of red is vertical and ends when the foot touches the floor

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Limb advancement is completed by knee extension

-

The hip maintains its flexion and the ankle remains dorsiflexed to neutral.

Determinants of Gait - Adjustments made by the body to minimize center of gravity movement - To achieve smooth sinusoidal (rhythmic) curve

Five determinants (adjustments) 1- Lateral pelvic tilt in the frontal plane • minimize the elevation of the COG

2- Knee flexion • minimize the elevation of the COG

3- Knee, ankle and foot interactions (synchronization) • minimize abrupt rise of COG

4- Pelvic rotation in the transverse plane • minimize the depression of the COG

5- Physiologic valgus of the knee • minimize width base of support

Lateral pelvic tilt in the frontal plane COG reaches the lowest and highest points of the sinusoidal curve during the double support and mid stance, respectively -

Figure 14-22 Sinusoidal curve - It’s leteral telting of pelvis (pelvis drop) on the side of the unsupported extremity (swing leg) • Produces adduction of the stance hip  Done by opposing hip abductors

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 i.e. pelvic drop during right extremity swing is controlled by left hip abductors -

Keeps the peak of the rise lower than if the pelvis did not drop.

- Figure 14-23

Knee flexion •

Knee flexion of the swinging leg at midstance, when the COG is at its highest point, represents another adjustment.

•

Helps to keep the COG from rising as much as it would have to if the body had to pass over a completely extended knee.

Knee, Ankle, and Foot Interactions • The synchronization of the knee, ankle, and foot movements provide smooth transfer of COG from lower to higher location • Prevent abrupt changes while the vertical displacement of the COG from a downward to an upward direction •

Moving COG upwardly from heel strike to foot flat is accomplished with knee flexion, ankle plantarflexion, and foot pronation. • The relative shortening of the extremity achieved with the combined movements of these body part provides the smooth rise COG after heel strike • Without these motions occurring together, the COG would rise abruptly after heel strike as the tibia rides over the talus.

• Figure 14-31 •

The interaction between the 3 body parts plays an important role when the body's COG falls after mid stance.

• Meanwhile the combination of ankle plantar-flexion, foot supination, and knee extension at heel off slow the descent of the body’s COG by a relative lengthening of the stance extremity.

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• Figure 14-33

Forward and Backward Rotation of the Pelvis • A small (~ 8°) back- & fore-ward hip rotations occur during lower extremity advancement

•

•

As the pelvis begins to move forward at preswing and continues as the swinging extremity advances forward during initial swing until reaching midstance (max. elevation of COG) is reached, the pelvis rotate forwardly to reach natural position.

•

Forward pelvis rotation continues beyond neutral on the swing side through terminal swing to initial contact.

Figure 14-24

• Meanwhile, an apparent lengthening of the lower extremities is occurring for both extremities (stance and swing) as the COG descends to its lowest level in the period of double support. • The swinging extremity is lengthened in terminal swing by the forwardly rotating pelvis • The weight-bearing extremity is lengthened in preswing by the posterior position of the pelvis. • This relative lengthening helps to prevent an excessive drop of the COG and maintains the COG at a higher level than would be possible if no pelvic rotation occurred.

Physiologic Valgus at the Knee • The physiologic valgus at the knee reduces the width of the base of support •

Narrower base of support result in little lateral motion of the body to shift the COG from one lower extremity to another over the base of support.

• Figure 14-25

KINEMATICS AND KINETICS OF THE TRUNK AND UPPER EXTREMITIES

(Trunk)

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• The trunk remains essentially in the erect position during normal walking with slight rotation primarily in a direction opposite to the direction of pelvic rotation. • As the pelvis rotates forward with the swinging lower extremity, the thorax on the opposite side rotates forward as well. • Helps preventing excess body motion and to counterbalance rotation of the pelvis. • Figure 14-37 • The erector spinae exhibit two periods of activity at heel strike and at toe off. • Prevent the trunk from falling forward. • The quadratus lumborum and the rectus abdominis are also active •

Precise function is not clear.

(Upper Extremities) • The arm swing opposite to the lower limps and similar to the trunk movements • The right arm swings forward with the forward swing of the left lower extremity, while the left arm swings backward. • counterbalance to the forward swinging of the leg and helps to decelerate rotation of the body caused by the rotating pelvis. • Figure 14-38 • The normal shoulder motion [~30° (24° ext. & 6° of flex.)] is the result of the combined effects of gravity and muscle activity. •

During the forward portion of arm swinging, the medial rotators are active (subscapularis, teres major, and latissimus dorsi).

•

In backward swing the middle and posterior deltoid are active throughout, while the latissimus dorsi and teres major are active only during the first portion of backward swing.

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• The supraspinatus, trapezius, and posterior & middle deltoid are active in both backward and forward swing. • The normal shoulder motion [~30° (24° ext. & 6° of flex.)] is the result of the combined effects of gravity and muscle activity. • Little or no activity is reported in the shoulder flexors. • The role of the middle deltoid is unclear, although it has been suggested that it functions to keep the arm abducted so that it may clear the side of the body. • Activity in all muscles increases as the speed of gait increases.

Muscle Activities

(Stance Phase) • Heel strike to Foot flat •

Figure 14-31

• Table 14-3

• Foot flat to Midstance • Figure 14-32 • Table 14-4

• Midstance to heel off • Figure 14-33 • Table 14-5

• Heel off to Toe off • Figure 14-34 • Table 14-6

(Swing Phase) •

Acceleration to mid swing

• Figure 14-35 • Table 14-7 •

Mid swing to deceleration

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• Figure 14-36 • Table 14-8