Lecture 4: GBS & Muscle Strengthening

Guillain-Barre Syndrome (GBS)

-Acquired immune-mediated inflammatory disorder of the PNS

-Similar presentation to LMN disorder

-Neurological signals are slowed, altered or blocked

What else is GBS known as?

-Acute Inflammatory Demyelinating Neuropathy (AIDP)

-Chronic Inflammatory Demyelinating Neuropathy (CIDP)

How is GBS caused?

-mostly by infectious respiratory or GI illness

-occur within 4 weeks of a preceding infection

Signs of GBS

-Loss of sensation

-Deep tendon reflexes are absent or reduced

-Paresthesia (pins & needles)

-Progressive muscle weakness

-Sometimes pain

-General fatigue

Motor & Sensory Involvement in GBS

-Typically symmetrical

-Distal muscles impacted first then proximal

-Progresses in ascending fashion

Variants of GBS

-Many

-Common forms: AIDP & CIDP

Topics in Muscle Strengthening

1. Neurological Muscle Weakness

2. Progressive resistance training (PRT)

3. Functional Strength Training

4. Sit to Stand (STS)

Paresis

-Partial weakness of muscle movement

-Still some limited voluntary movement but impaired control

Paralysis

-Complete loss of muscle movement

Weakness/Paralysis/Paresis

-Can occur in either UMNL or LMNL

-However, paralysis is more common in LMNL and paresis is more common in UMNL

Why do we have muscles?

-Torque generation

-Joint stability

-Postural stability

-Circulation

-Shock absorption

What determines muscle strength in terms of torque generation?

-Structural, mechanical and neural factors

What structural factor primarily influences muscle strength?

-Muscle size, specifically cross-sectional area (CSA)

-The larger the muscle, the larger the force generation

What are the key mechanical factors that influence torque generation?

-Speed (Force-velocity)

-Type of contraction (eccentric vs concentric)

-Load

-Length-tension

What are the neural factors affecting muscle strength?

-Motor unit size

-Number of motor units activated

-Recruitment order

Muscle Fibre Types

-Type 1 (Slow Oxidative)

-Type 2A (Fast Oxidative)

-Type 2B (Fast Glycolytic)

Speed (Force-Velocity)

-When a muscle shortens quickly, (high velocity concentric contraction), it produces less force

-Contracting slowly can produce more force (muscle lengthening under tension)

-Cross-bridges have less time to form at high speeds

-Muscle lengthening under tension: muscle generating a lot of tension to prevent rapid lengthening, holding on against the pull = higher torque/force

Load (Torque Generation)

-A heavier load requires a greater torque to move it

-If the load exceeds the muscle torque's capacity = no movement (isometric)

Type 1 Muscle Fibre

-Slow oxidative fibers contract relatively slowly and use aerobic respiration

-Produce low power contractions over long periods

-Slow to fatigue

*more for endurance activities

Type 2A Fibers

-Fast oxidative fibers that have fast contraction and use aerobic respiration but can switch to anaerobic

-Fatigue more quickly than type 1 (intermediate)

*more for power movements

Type 2B Muscle Fibers

-Fast glycolytic fibers that have fast contractions

-use anaerobic glycolysis

-Fatigue the quickest

*more for power movements

What is a general sign of neurological weakness?

-Impaired magnitude of force: muscle cannot generate its usual maximal strength

How can neurological weakness affect force scaling?

-Pts may have difficulty adjusting the amount of force for a task (producing too much or too little)

How is the speed of force production impacted in neurological weakness?

-muscles take longer to reach peak force

What happens with repeated contractions in neurological weakness?

-Rapid onset of fatigue

-Strength drops quickly with repeated use

How does neurological weakness impact the perception of effort?

-Pts feel like they are applying an excessive amount to perform normal tasks

Why Might Force Production be ineffective in voluntary tasks?

-Timing problem

-Not just strength, but muscles may not contract at the right moment

What is notable about the onset of neurological muscle weakness?

-May have a rapid onset, unlike gradual disuse weakness

How is the pattern of weakness typically distributed?

-Diffuse rather than a single isolated muscle or group

What are the key signs of neurological muscle weakness?

-Impaired magnitude of force – reduced maximum strength

-Impaired scaling of force – difficulty adjusting force for tasks

-Slowness of force production – takes longer to reach peak force

-Rapid onset of fatigue – weakness appears quickly with repeated contractions

-Excessive sense of effort – normal tasks feel harder than expected

-Difficulty producing force effectively during voluntary tasks – may be a timing problem

-Onset of weakness – can be rapid

-Pattern of weakness – often diffuse, not isolated

(SLOW FATED)

Structural Factors Impacting Muscle Weakness

-Reduced muscle mass & increased intramuscular fat content

-Change in fiber distribution with reduced slow twitch fibers

Neural Factors Impacting Muscle Weakness

-Motor Unit loss

-Increased motor unit innervation ratios

-Altered motor unit properties

How does motor unit loss contribute to muscle weakness?

Fewer motor units → fewer muscle fibers can be activated → reduced force generation

What is the effect of increased motor unit innervation ratios?

Surviving motor neurons innervate more muscle fibers to compensate → less precise and slower force production

Aging Factors Impacting Muscle Weakness

-Behavioural Factors

-Physiological Factors

Behavioural Factors

-Immobilization

-Physical Inactivity

Physiological Factors (AGING)

-Increased time for synaptic transmission

-Decreased nerve conduction velocity

Can Aging Related Factors to Muscle Weakness be Offset?

-Yes, through regular physical activity/exercise

-Adipose tissue generation is put off

What are some assessment related factors that can affect muscle torque measurement?

-Tool used

-Therapists skill and strength

-Placement of external resistance

What patient-related factors can influence muscle torque generation?

-Time of day

-Sex

-Pain or swelling

-age

-Comprehension of instructions

Assessing Strength - MMT

5 grades

-Used to assess pt's muscular strength

-Below 2 is all gravity eliminated

-above 2 is all against gravity

* 2, 2+, 3-, 3 ....

What do the +'s and -'s mean in MMT Grading?

+ = Less than 1/2 the available ROM available (either against gravity or gravity eliminated)

- = Greater than 1/2 the available ROM (either against gravity or gravity eliminated)

Principles of Muscle Strengthening

1. Progressive Overload

2. Task Specificity

Progressive Overload (PRT)

-gradually increase resistance during exercise

-Muscles adapt only when challenged to exert a greater force

-Using the same force will lead to plateau in strength gains

*Apply to 1 muscle

Task Specificity (Functional Strength Training)

-Strength gains are specific to:

*muscle action (ex: biceps flex, not abduct)

*contraction

*Speed of movement (endurance vs power)

*ROM

*Intensity/volume

Muscle Strengthening Approaches

-Progressive Resistance Training (PRT)

-Functional Strength Training (task related)

Benefits of PRT

-Promotes bone health

-Most effective when combined with functional mobility

-Does NOT worsen Spasticity

-Improve muscle strength & hypertrophy

**More effective in pts with less severe deficits

Mechanisms of PRT

-Structural (increase CSA)

-Neural (enhances motor unit recruitment and firing rates)

Contraindications to PRT

-CV Risks:

*Unstable angina

*Recent MI

*Severe Aortic Stenosis

*Uncontrolled hypertension

Spasticity is not one!

PRT Exercise Recommendation for Novice Trainers

F: 2d/wk

I: 60-70% 1RM

T: 8-12 reps for at least 1 set

PRT Progression

1. Increase load (~2-10% when able to lift current load for 1-2 extra reps on 2 consecutive sessions)

2. Add reps (with same load up to ~12)

3. Alter rep speed (vary temp)

4. Add sets

5. Reduce Rest time (increases intensity)

*Program should last 6-12 weeks

Methods to Determine 1-RM (maximal load)

-Direct 1RM

-Indirect 1RM

Direct 1RM Method

-Practice movement and breathing first

-Apply estimated load for 1 lift

-Provide a 2 min rest, adjust up or down, and repeat until found

*usually not confused for neurological population due to weakness mentioned in other flashcard

Indirect Method

-Use submax reps (<10 reps) to predict

-Use Eqn to calculate

*safer for neurological population

3 Components of Resistance Training

1. Muscle Strength (force generation)

2. Muscle Endurance (force generation without fatigue)

3. Muscle Power (how quickly a muscle can generate force to produce a movement)

Parameters for Muscle Strength (Resistance Training)

I: >60% 1RM

T: 8-12 reps for 1-3 sets

Rest of 2-3 mins

Parameters for Muscle Endurance (Resistance Training)

I: <50% 1RM

T: 15-25 reps for 1-3 sets

Rest of 1-2 mins

Parameters for Muscle Power (Resistance Training)

I: 30-60% 1RM high velocity

T: 3-6 reps for 1-3 sets

Rest for 2-3 min

Functional Strength Training (FST)

-Practice meaninful ADLs and precursor activities with repetitive practice and therapeutic intensity

-Better for low-level strengthening (weaker pts)

-Does not increase spasticity, unless movements provoke clonus

-Focus on task-specific functionality, not individual muscles

Examples of Functional Strength Training

UE:

-Repetitive reaching

-grasping objects of different sizes/weights

LE:

-Sit-to-Stand

-Rise-to-walk

-Heel raises

-Stair climbing

-walking with weights

*Load is not precisely quantified

Sit-to-Stand (STS) Importance

>40% adults of neurological disability struggle with this

Reason for difficulty with STS

-Weakness being the major factor

-balance and vestibular deficits

4 Phases of STS

1. Forward weight shift (flexion momentum)

2. Loading (momentum transfer)

3. Extension (lift)

4. Stabilization (end hip extension)

Essential Requirements of STS

1. Strength for smooth lift

2. Trunk & LE stability to transfer COM from chair's to own BOS

3. Adaptability for varying environments

Stand-to-Sit

-Requires eccentric control, esp of quads

-Adequate PF length for knee forward movement

Stairs

*significant determinant of independence & active community living

Ascent:

-Higher strength demands

Descent:

-Requires more eccentric control

Approach to Muscle Strengthening in GBS

-Hydrotherapy for pain relief, functional strenthening and early mobilization

-Avoid overloading weak muscles (paradoxical weakness)

-Avoid over-lengthening weak muscles

Recovery & Long Term Considerations for GBS

-Rapid recovery within 6 months with significant improvement in 18 months

-Grip strength may plateau at 1yr

-Fatigue, pain, anxiety/depression can persist and affect QoL

-Risk of return of weakness later in life

What is the risk in GBS Recovery?

-Weakness may return later in life

What 3 symptoms can persist in GBS?

-Anxiety/depression

-Fatigue

-Pain

How long does recovery take in GBS?

-Rapid within 6 months (self-limiting disease)

-Significant improvements in 18 months

*regardless of PRT or FST (but can help accelerate recovery and prevent long term complications)

What is permanent weakness in GBS associated with?

-Age

-Severity at nadir (lowest point of functioning)

-Permanent weakness from axonal loss

-Duration on mechanical ventilation

Long Term GBS Patients

1 yr post: 1/3rd recovered, 1/3 UE weakness + sensory issues

7yr post: 50% have some weakness (mostly distal UE)

Why should FST be incorporated for more severe pts before PRT?

early on you want to just work on getting people back to their daily tasks so functional would be priority