L6 - Gait Flashcards by Sofia Courtis

What is concentric contraction?

Muscle shortens as it contracts.
–> the most common type of muscle contraction

When you actively lift a weight or move a body part against resistance.

Example: When you curl a dumbbell during a bicep curl, the biceps shorten as you lift the weight.

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What is eccentric contraction?

Muscle lengthens while still under tension.

When a muscle is resisting a force that’s greater than its contraction force, like lowering a weight slowly.

Example: When you lower the dumbbell back down in a bicep curl, your biceps are lengthening under tension, controlling the descent.

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What is isometric contraction?

Muscle generates force without changing its length.

When you hold a position without moving.

Example: Holding a plank or holding a weight in a fixed position without moving it.

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What is a gait cycle?

Movement beginning and ending with ground contact of the same foot (e.g. right heel strike to right heel strike).

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What are the 2 parts of the gait cycle + proportion?

Stance (~60%)
Swing (~40%)

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What is a step?

Movement of a limb (e.g. right) from ground contact of one (e.g. left) to ground contact of opposite limb (e.g. right).

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What is a stride?

Movement of both limbs during 1 gait cycle (2 steps).

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What is cadence?

Steps / min

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What are the 2 ways to walk faster?

Increase cadence (steps/minute)
Increase step length

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What is the difference between walking and running?

Walking: always a foot on the ground, sometimes even 2
Running: there is a flight phase = no feet on ground

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Name the phases of the stance phase. (5)

Initial contact
Loading response
Midstance
Terminal stance
Preswing

See NDC p.7 for illustration

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Stance Phase
What is initial contact?

Instant the foot contacts the ground.

See NDC p.7 for illustration

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Stance Phase
What is loading response?

Time period from immediately following initial contact to the lift of the contralateral extremity from the ground, during which weight shift occurs.

See NDC p.7 for illustration

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Stance Phase
What is midstance?

Time interval from lift of the contralateral extremity from the ground to the point where the ankles of both extremities are aligned in the frontal (or coronal) plane.

See NDC p.7 for illustration

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Stance Phase
What is terminal stance?

Period from ankle alignment in the frontal plane to just prior to initial contact of the contralateral (swinging) extremity

See NDC p.7 for illustration

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Stance Phase
What is preswing?

Time interval from initial contact of the contralateral extremity to just prior to lift of the ipsilateral extremity from the ground (unloading weight)

See NDC p.7 for illustration

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What phases of the stance phase have double support?

Loading response
Preswing

See NDC p.7 for illustration

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Name the phases of the swing phase. (3)

Initial swing
Mid swing
Terminal swing

See NDC p.8 for illustration

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Swing Phase
What is initial swing?

Lift of the extremity from the ground to position of maximum knee flexion.

See NDC p.8 for illustration

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Swing Phase
What is mid swing?

Immediately following knee flexion to vertical tibia position.

See NDC p.8 for illustration

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Swing Phase
What is terminal swing?

Following vertical tibia position to just prior to initial contact”.

See NDC p.8 for illustration

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What is the goal of gait?

Progress forward.

What are the goals of the stance phase? (3)

Provide support
Absorb shock
Provide forward and backward force for progression

What are the goals of the swing phase? (3)

Limb clearance
Limb placement
Transfer momentum

What devices measures joint angles during gait?

Electrogoniometer

Are joint angles kinematic or kinetic variables?

Kinetic variable See NDC p.10 for exercise of sagittal joint angle identification

Name the center of mass (COM) displacements in the body?

1. Lateral displacement in horizontal plane 2. Vertical displacement 3. Combined displacements of lateral/vertical See NDC p.11 for illustration

Describe lateral displacement of the COM.

When on left stance = COM goes left When on right stance = COM goes right See NDC p.11 for illustration

Describe vertical displacement of the COM.

When on double stance = COM goes down When on single stance = COM goes up See NDC p.11 for illustration

Describe combined lateral and vertical displacement of the COM.

Makes an infinite symbol. See NDC p.11 for illustration

Name the ground reaction forces during gait.

1. Vertical GRF 2. Anterior-posterior GRF 3. Medial-lateral GRF See NDC p.12 for illustration

What is the formula for vertical GRF?

∑Fy = may GRF - W = may GRF = W + may See NDC p.13 for illustration

What does it mean if ay is positive or negative? When is ay positive during the gait cycle?

GRF = W + may - ay : GRF < W = GRF < 100BW + ay : GRF > W --> GRF > 100BW 1. At the beginning of stance 2. Around pushoff --> COM is at its highest point See NDC p.13 for graphs + more details

In anterior-posterior GRF, when is it positive and negative?

Posterior GRF = - GRF Anterior GRF = + GRF

Describe at what times of the gait cycle is anterior-posterior GRF positive and negative?

At heelstrike, heel is pushing forward so GRF is pushing backward: posteiror = negative (-) At pushoff, toes are pushing backward so GRF is pushing forward: anterior = positive (+) See NDC p.14 for graph

Why not calculate each muscle force separately?

Too many unknowns. We only have 6 equations in 3D.

What is inverse dynamics?

Calculate net joint forces and moments of force (torque) from: - kinematics information (ex: acceleration), - inertial properties (ex: mass) - external forces (ex: ground reaction force)

What is forward dynamics?

We know the forces in muscles, joints, etc. and predict movement. The "know" based on data

How do we deconstruct inverse dynamics problems? What is the assumption in these problems?

Link segment: we break the body into different segments --> ex: foot, shank, thigh *Assumption: Each segment is rigid We work our way up/down each segment. See NDC p.17 for illustration

Name Newton's Law used in inverse dynamics problems. (2)

Newton’s 2nd law: unbalance force produces an acceleration - ∑F = ma; ∑M = Iɑ --> ɑ= angular acceleration Newton’s 3rd law: for every force, there is an equal (magnitude) and opposite (direction) force

Name the formula for a static and dynamic problem in inverse dynamics.

Static equilibrium = forces balanced, no acceleration - ∑F = 0; ∑M = 0 Dynamic equations = force unbalanced, acceleration - ∑F = ma; ∑M = Iɑ

What are the limitations of inverse dynamics?

1. Cannot determine individual muscle forces due to co-contraction --> we assume one group is active 2. Sensitive to input data (GRF, anthropometrics)

What causes net external moments VS net internal moments?

External = Moments applied to the joint due to external forces (e.g. GRF, gravity) Internal = Moments applied to the joint by muscles and soft tissue --> We flip the graphs See NDC p.22-25 for illustration

How do measure muscle activation? What can we measure?

Measured using electromyography (EMG) Eccentric, concentric, and isometric contractions

What type of muscle activation occurs the most during gait?

Eccentric muscle contraction --> Walking is controlled falling See NDC p.27 for table

See NDC p.28-32 for graphs of muscle activation

See NDC p.33 for concentric VS eccentric contraction identification

;)

What is joint power?

Power = rate of doing work (in watts) P = point moment · angular velocity = M · ω

What is the sign of power in concentric VS eccentric contractions?

1. Concentric = generate power (+ive) 2. Eccentric = absorb power (-ive)

In what joints/muscles is power generated during the gait cycle?

Power generated = + power by: 1. Hip: flexors and extensors --> beginning of stance: heel strike --> beginning of swing: swinging leg forward 2. Ankle: plantarflexors --> pushoff See NDC p.35 for graph

See NDC p.36-42 for exercises + week 8 lab GOOD FOR FINAL! What are the 2 criteria to determine the sign of power?

1. Sign of power graph 2. Is muscle contracting during designed movement? --> does movement match function?

What is the stretch-shortening cycle?

Muscle activity starts eccentric contraction (stretch) then switches to concentric contraction (shortening)

Why do muscles follow a stretch-shortening cycle?

Efficient way to generate muscle force and store energy --> Energy stored in stretched muscle in anticipation for the concentric contraction ex: As we advance over foot, foot is dorsiflexing under the control of gastrocs. At pushoff, stored energy used for concentric contraction at plantarflexion See NDC p.43 graph