Immobilization and Rehabilitation

IMMOBILIZATION

ATROPHY FACTORS

1) Species

2) Fibre composition of muscle

3) Length of time immobilized

4) Position of joint fixation

5) Specific muscle

Effects of Immobilization:

• Atrophy: dependent on:

duration of immobilization;

degree of stretch

– FIBRE DISTRIBUTION : in humans a type I to type IIb conversion has been reported

– Possible preferential atrophy of type I fibres dependent on consistent impulse activity

IMMOBILIZATION

PREFERENTIAL ATROPHY OF ONE FIBRE TYPE?

Possible Reasons:

1) Time: ST need regular neural input and may therefore be the first affected

2) Afferent Feedback: ST receives a greater density of afferent feedback, therefore immobilization may affect ST more severely

IMMOBILIZATION

Decrease in Muscle Activation (ITT) EMG, reflex potentiation, firing frequency

Immobilization Activation Decrease

3) Position of Immobilization: a multi-muscle joint may have one muscle in a more or less stretched position than another affecting the rate of atrophy

– Shortened position results in an increase in protein degradation and decrease in # of sarcomeres

4) Extent of Training: if FT fibres have been previously hypertrophied through training, then the return to baseline will be more significant for the FT than the ST

PROTEIN COMPOSITION: decrease in myofibrillar protein with a sparing or an increase in stromal and soluble protein concentrations

PROTEIN TURNOVER:decrease in protein synthesis with increased protein degradation occurring with longer periods of immobilization

MUSCLE METABOLISM: depending on duration of immobilization, glycolytic and oxidative enzymes are either decreased or unchanged

FORCE GENERATING CAPACITY:

- decrease in both absolute and relative voluntary and evoked contractile force

- decreased reflex potentiation

- decreased EMG

- decreased tetanus

FATIGUE CHARACTERISTICS: no significant change in voluntary isometric, dynamic or evoked fatigue characteristics Why? If atrophy occurs, decrease in SDH?

ELASTIC PROPERTIES OF MUSCLE:

tensile strength of a muscle decreases with immobilization; important consideration for ROM exercises

EFFECTS ON BONE: loss of bone mass and size

EFFECT ON LIGAMENTS AND TENDONS: decreased tensile strength and thickness

EFFECT ON JOINTS:degeneration and atrophy of articular cartilage and joint stiffness; may be due to a lack of joint loading and movement

Training Strategies for Neuromuscular Adaptations:

1) Isometric Contractions: debatable effectiveness; possibly related to contraction intensity; submaximal do not activate high threshold MU; decisive factors: Mobility Fatigue

2) Electrical Stimulation more consistent results alterations in motor unit recruitment?

3) Answer: Combine isometric contractions and E-stim normal recruitment pattern and activation of high threshold motor units

4) Cross education: in healthy subjects contralateral limb strength increases 15%

no research on immobilized

5) Stretch; increased protein degradation with lack of stretch, thus need to activate stretch receptors

6) Imagery: Yue and Cole study;

Imagined contractions increased force of abductor digiti minimi by 20% versus 30% increase with training

no research on immobilized

Post-Immobilization Strategies :

•Extensive early rehab may not provide greater benefits

•Most studies have not included a control group

•Some animal studies have shown decreased responses with greater volume of early rehabilitation

•Overtraining

•Most important variable: INTENSITY

Training Specificity:

•Angle

•Contraction type

– Concentric: least number of crossbridges greatest crossbridge cycling rate

– Isometric: greatest number of crossbridges

– Eccentric: greatest number of crossbridges Altered recruitment patterns Less MU recruited / load results in Greater tension / muscle fibres

•Velocity

Rehabilitation

Velociy Specificity

•Strength gains are accrued at or near the training velocity with decreased benefits as the training velocity deviates from the testing velocity

•Early studies emphasized movement speed

•Behm and Sale 1993 suggested most important factor is CONTRACTION SPEED

•Importance related to: Specificity Firing frequency (neural adaptation); Motor control (ie ballistic contractions).

• Other Rehab Considerations: Closed Kinetic Chain Exercises

•Biofeedback or Visual feedback

IMMOBILIZATION

Summary of Techniques

During Immobilization

•ROM and stretch Isometric

•contractions with electrical stimulation

•Training of contralateral limb

•Imagery

Post-Immobilization

•Variety of isometric angles

•Dynamic concentric and eccentric contractions

•Higher speed contractions moving to ballistic

•Closed Kinetic chain

•Bio or visual feedback

RECOVERY FROM IMMOBILIZATION :

•Spontaneous recovery:evidence of both complete and incomplete recovery - Why?; joint mechanics; altered lifestyle; insufficient rehabilitation; inability for full muscle recovery

•Post-immobilization Training:in animals, training accelerates muscle function; in humans, some similar evidence but a lack of control groups; factors - intensity, volume, onset of training

•Osteoarthritis: increase in % of ST fibres

•Muscle Transplantation:ischemic necrosis followed by regeneration; effect of exercise; no beneficial effect of early intervention

IMMOBILIZATION

Strategies:

•Isometric Training:submaximal contraction due to pain inhibition?

•Electrical Stimulation: reverse order of recruitment; analgesic effect; compliance

•Cross-Education

•Stretch