Exam 2 Content

Maximize stability/balance

• Increase BOS

• Lower COM

• This can restrict mobility

Maximize mobility

• Small BOS

• COM located outside or near the boundary of bos

Strategies to counteract instability at the feet and anke

• Distal to proximal

• Aim to maintain COM within the BOS

• perturbations is slow and small amplitude

• Firm contact surface

Anterior Sway at feet and ankle

• Fall into DF so use ankle plantar flexors and toe flexors to return

• Contractions of gastrocnemius, posterior tibialis and toe flexors

Posterior Sway at the feet and ankles

• Fall into plantar flexion so use ankle dorsi flexion and toe extensors to return

• Contraction of tibialis anterior and toe extensors

Strategies to counteract instability hip to pelvis

• Proximal to distal

• aim to move COM relative to bos by moving the trunk

• perturbation is fast and large amplitude

• unstable contact stable

Anterior Sway hip to pelvis

• Fall into hip flexion so use hip extensors to extend pelvis and hip and return to normal alignment

• Contractions of gluteus maximus and hamstrings

Posterior Sway hip to pelvis

• Fall into hip extension so use abdominals and hip flexors to return to normal alignment

• Contractions of iliopsoas, rectus femoris, and abdominals

Steps to counteract instability for falling

• Aim to increase BOS and prevent falls

• Step in direction of displaced COM

• Used more in elder and clinical populations due to:

• Reduced muscle strength-force production

• slower reaction, muscle activation times

How to improve stability

• Target strength (ankle, hip, and core)

• Simulating step strategy (fall prevention)

• Balance metastability

Metastable Def.

Exercising in a state of dynamic balance where stabilizers muscles constantly adjust to moderate disturbances

What is equilibrium?

Relationship between center of mass and base of support

What is balance?

• Ability to keep COM within BOS

• Fundamental to ADL’s and athletic performance

• Both a static and dynamic state

Stability

when COM returns to original position after a slight disruption, resistance to being at a new location

Instability

when COM is away from its original position

Degree on stability depends on:

1) Height of COG above BOS: Lower the more stable

2) Size of BOS: Wider the more stable

3) Location of gravity line within BOS: over center of support is more stable

4) Weight of body: heavier is more stable

What are limits of stability based on COM?

• Distance a person can move their COM without losing balance or taking a step

• Determined by: position of COM/ Velocity of COM

Maintaining “correct” static posture

• It reduces the development of pathological conditions over time

• It minimizes muscular effort

• It decreases abnormal joint and tissue stresses

• It keeps the body as close to equilibrium as possible

How to quantify vertical reaction forces and how the data is used?

• To isolate the weak and poorly moving lower extremities

• For sport performance profiling

• To assess post-injury progress and readiness for return to sport

• To quantify acute neuromuscular fatigue after an intense exercise training or competition session

What upper extremity muscles need to be strengthened for a person with upper cross syndrome?

• Lower Trapezius

• Rhomboids

• Neck flexors

Length-Tension Def:

Relationship between muscle length and force the muscle can produce at that length?

What muscles contract eccentrically during the unweighting phase of the CMJ?

• Gluteal muscles (hip extensors)

• Gastrocnemius and Soleus

• Quadriceps

What muscles need to be strengthened in a lower crossed syndrome?

• Abdominals

• Gluteus maximus

What soft landing strategies can help minimize injury

• The trunk should not flex laterally at initial contact

• The feet should be shoulder width adapt

• The knee joint should be flexed at initial contact

How do you minimize risk of lower extremity injuries?

• Decrease vertical ground reaction force

• increase time to peak force —> decrease rate of loading

• Maintain sagittal plane alignment

During the propulsion phase which muscles are concentrically contracting?

• Gluteal muscles

• Quadricep muscles

• Gastro

Passive tension def:

When a muscle lengthens, the series and elastic components become taut, providing stiffness to the muscle and contributing to a more forceful muscle contraction

Force-velocity curve for a muscle contracting concentrically

The greater the velocity, the less force the muscle can develop

The slower the velocity, the more force the muscle can develop

What makes a muscle contracting eccentrically more efficient than concentrically?

contribution of passive tissues

How would you increase vertical jump performance?

• Perform plyometric exercises that focus on minimizing the amortization phase of landing and jumping

• Perform exercises that increase the eccentric contraction velocity of the muscles

• Perform exercises that accentuate the stretch-shortening cycle

• Perform slow-velocity concentric contractions of the lower extremities

What are direct force measurements?

• Force plates

• Pressure mats

What are indirect force measurements?

• Hand held dynamometers

• Isokinetic dynamometers

• Accelerometers

• Performance tests

What is the CMJ? How do we assess it? What does it correlate with

CMJ: Quantifies vertical reaction forces during a jump

Assess:

• Power

• Fatigue

• Changes in performance

Correlates with:

• Sprinting

• Sprint Cycling

• Olympic lifting

• Changing direction

Phases of CMJ

1) Weighing phase: weigh athlete for at least 1 sec

2) Unweighting phase: Lowering/loading, pre-stretch; lengthening muscles increase passive tension; triggers stretch reflex (Rapid lengthening)

3) Breaking phase: time for muscles to transition from eccentric —> concentric contraction; shorten to improve energy efficiency and performance

4: Propulsion phase: concentric phase; push-off phase

• propulsive, unloading phase that produces

• Hip extension, Knee extension, ankle plantar flexion

5) Flight phase: athlete leaves platform with intention of attaining maximal height. Velocity should be peak 0

6) Landing phase: deceleration; eccentric contractions to absorb GRF

• Need the core to stabilize LE

Speed of Contraction Def:

velocity at which a movement occurs/muscle contracts affects amount of force produced by muscle

What is a Hop Battery test? What are the 4 tests to assess?

series of single-leg functional jump tests used to evaluate lower limb strength, power, symmetry, and readiness to return to sports after an injury especially ACL and reconstruction

• Single Leg Hop

• Triple hop

• Crossover triple hop

• Six meter timed hop

Limb Symmetry Index

Performance on injured leg is compared to uninjured leg

(_ / _) x 100 = %

Passing: Requires an LSI of > or = 90%

Posture def

position of body at any given point in time, sitting, standing

Changes in posture lead to:

• musculoskeletal

• musculotendinous

• myofascial

• CNS +PNS

Total Tension

Combining of passive and active force that makes up the total force to produce force at various lengths/joint angles

Active tension

Amount of force produced by a muscle is dependent on length of muscle fiber which relates to the amount of overlap between actin and myosin

Passive tension

tension to muscle force within parallel elastic components and series of elastic components

Why perform a postural assessment?

1) Establish a baseline for movement

2) Identify compensatory strategies/positioning

3) Identify muscle imbalances

Stance phase

Closed chain; weight bearing

• Begins with initial contact

• Ends as foot no longer in contact with ground

• 60% of gait cycle

Swing phase

Open chain; non-weight bearing

• begins with initial swing

• ends with next initial contact

Initial Contact

Begins when foot touches supporting surface

Contact made through posterolateral aspect of calcaneus with supinated foot

Muscle activity:

• Contractions of the anterior and posterior lower leg muscle to stabilize ankle with foot supinated

• Quadriceps concentrically contract to extend knee joint

• Co-contractions of quadriceps/hamstrings to stabilize knee joint

• Gluteus maximus and hamstrings contract eccentrically to decelerate hip flexion

Loading response

Absorb GRF and support body mass as limb is decelerating

Foot pronates and ankle moves to plantar flexion:

• absorb vGRF

• Tibial anterior (ankle dorsi flexor) eccentrically contracts to lower the foot to ground

Knee flexes to approx. 15-25 degrees

• eccentric quadriceps contract

Hip muscles stabilize with weight transfer to single leg stance

• gluteus maximus contracts isometrically or eccentrically to prevent trunk flexion

Midstance

Transitions from decelerations to accelerations

• Foot is stationary single limb support

• Body advances over support limb

• Foot initiates supination

• Ankle is in CKC dorsiflexion

• Hip moves into extension

• Trunk is aligned over stance: hip abductors stabilize pelvis in frontal plane to prevent pelvis drop

Terminal Stance

Goal: create a propulsive force

Ankle is in plantarflexion and great toe is extended

Preparation for swing

• knee flexes, hip extends

• concentric muscle contractions to accelerate and push body forward onto the contralateral limb

Trunk moves ahead of stance foot

Ends before contralateral limb makes IC with ground

Preswing

Goals:

• Accelerations/propulsions through concentric contractions

• 2nd period of double support—> transitioning between weight bearing legs

• Greater toe hyperextension increases height of medial longitudinal arch by tightening the plantar fascia (stabilizes midfoot so toe can push off)

• Hip flexors begin contracting to clear the limb during swing phase

Swing phase

40% of gait cycle

OKC

Relatively low energy phase

Goals:

• Achieve foot clearance

• Advance limb

• Position limb for next stance phase

Initial Swing

Begins when foot leaves ground following preswing

Single leg stance

• Opposite limb is in midstance

• Pelvis is stabilized by hip abductors

Foot Clearance:

• Hip flexion, knee flexion, ankle dorsiflexion

Acceleration of swing leg-hip flexors (iliopsoas, rectus femoris) and ankle dorsi flexors (tibialis anterior)

Momentum of limb is primarily responsible for knee flexion, not concentric contraction of hamstrings

Ends when knee reaches maximum flexion

Midswing

Begins as knee extends from maximum flexion until tibia reaches a vertical position perpendicular to surface

• Knee extension is due to concentric contractions of quadriceps

• Hamstrings are eccentrically contracting to control motion

• Femur continues to advance anteriorly

• Ankle dorsiflexion so toe clearance is ensured

Terminal Swing

Pelvis rotates forward in transverse plane to advance leg

Deceleration of hip flexion to prepare for initial contact

• Eccentric contraction hamstrings and gluteus maximus

Knee extends to create step length

Quadriceps contract to extend knee and prepare the limb for weight bearing

Foot supinates to be rigid at IC

• Co-contractions of ankle muscle to stabilize

Upper Body movement during gait

Reciprocal arm swing

• acts as a counterbalance to lower extremity movement

Utilizes posterior and anterior oblique sling system

• Posterior: R hip extension, L shoulder extension

• Anterior: R hip flexion, L shoulder flexion

Eliminating arm swing

• requires 12% more metabolic energy

• increase vGRF by 63%

Step-length

linear distance covered by 1 leg

Typically between 0.6-0.8 meters

Stride-length

Linear distance covered by a stride

Step Width

distance between 2 points of contact of both feet

Stride duration

time it takes to perform 1 stride

Cadence

Steps per min

Avg. 90-120 steps/ min

Women have higher cadence

Speed/velocity

Distance traveled in a period of time

m/s

known as 6th vital sign in geriatric population

Sacropenia: loss of muscle mass leads to decrease force and power production

loss of muscle mass leads to decrease force and power production