Isokinetics in Rehabilitation

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Isokinetics in Rehabilitation
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Isokinetic Exercise

• Hislop Perrine (1967) - movement that occurs at
  a constant angular velocity with accommodating
  resistance
• max muscle tension can be generated because
  resistance is variable to match the muscle
  tension produced at various points in the ROM!

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Isotonic vs. Isokinetic Exercise
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Advantages

• 1) isolate weak muscle groups
• 2) work maximally throughout ROM
• 3) velocities simulate functional activity?
• 4) inherent safety mechanism

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Disadvantages

• 1) cost
• 2) open-chain motions
• 3) cardinal planes

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Terminology

• 1) force - when a stimulated muscle acts against
  a resistance force is produced
• 2) torque - F x D (from fulcrum or axis of
  rotation)
• 3) work - applied force times distance of
  rotation
• 4) power - time required to perform work

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Normal Torque Curve

• 1) Angle Specific Torque (AST) -
• 2) Peak Torque (PT) -
• 3) Average Torque (AT) - torque over entire ROM
• - lower than PT, higher reliability

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Isokinetic Curves
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Isokinetic Curves
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Power Curves
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Abnormal Torque Curve

• Predicting Injury from Curve?
• can look at pt of pain, but not predict injury!
• non-volitional reproduction of pain at the same
  pt in ROM
• isokinetics will accommodate the pain by
  decreasing the dynamometer force

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Types of Dynamometers

• Passive - primary function is the dissipation of
  energy
• torque produced by the pt driving the dynamometer
• old Cybex systems
• Active - robotics, can either dissipate energy
  by the patient or supply energy to do work on the
  patient
• Kin Com, Biodex, Cybex

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Instrumentation

• Mode of Muscle Action
• con/ecc
• isometric
• passive
• Test Velocity
• 0?/s - 1000 ? /s
• above 300 ? /s difficulty generating force (not
  isokinetics!!)

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Principles of Isokinetic Strength Assessment

• 1) Musculoskeletal and CV. Screening
• 2) Pt. Education/Familiarization
• 3) Stabilization/Joint Alignment
• 4) Gravity Correction
• 5) Test Velocity

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Gravity Correction

• Must be performed during any gravity dependent
  joint testing position
• GC value to force ?
• GC value (-) to force ?
• some dynamometers perform this either dynamically
  or stationary
• Failure to GC results in
• quads under predicted
• hams over predicted

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Confounding Factors to Accurate Isokinetic
Evaluation

• Assess strength not PAIN!
• Joint effusion (neuro-inhibitory effect)
• Muscle co-activation (hams contract near terminal
  ROM with knee extension may effect AT!)

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Test Protocols

• 1) interrupted - test repetitions separated by a
  time period
• greater reliability
• 2) continuous - no pause between test repetitions
  better predictor of PT (peak torque)
• 3) sequencing - con/con, con/ecc, ecc/ecc, ecc/con

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Interpreting an Isokinetic Evaluation

• 1) Torque, Power, Work -
• - all have high r values
• - AT more reflective of pts capability to
  generate force thru ROM
• 2) Muscle Endurance -
• 3) F-V Relationships -
• - differences con vs. ecc

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Factors affecting muscular force generation

• Force-velocity relationship
• concentric

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Factors affecting muscular force generation

• Force-velocity relationship
• Concentric/eccentric

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F-V R Curve Knee Flex Ext
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FV-R Ankle Eversion
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Interpreting an Isokinetic Evaluation

• Force/Torque ratios Relative to BW -
• Nm torque/kg BW
• mainly involving the lower extremity
• Bilateral Muscle Group Comparisons
• Reciprocal Muscle Group Comparisons
• Knee flex/ext (HQ) .67 ratio
• Shoulder ER/IR .70 - .90 (.65 ?M .80 ?F)
• Shoulder ABD/ADD (1.0 ?M 2.0 ?F)
• Ankle E/I Ratios .65 - .90

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E (CON) I (ECC) Ratios in the Ankle

• Trend is for ratios to be lt 1.0 why?
• ECC strength values in the denominator will in
  most cases be greater than the CON values found
  in the numerator
• ? 40 greater force production ECC
• less CON force generated at the higher velocity
  (120/sec) lowers the ratios at the higher speeds
• Lack of normative values for comparisons

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E (ECC) I (CON) Ratios in the Ankle

• Trend is for ratios to be gt 1.0 why?
• ECC strength values in the numerator will in most
  cases be greater than the CON values found in the
  denominator
• ? 40 greater force production ECC
• Interesting to note that at the higher velocity
  (120/sec) that the ratios are elevated
• ECC force production in the ankle typically rises
  from the slower velocities to peak around 120/sec

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Implications

• Normative values are needed to allow for
  meaningful comparisons
• Will prove useful for clinician
• rehab goals
• return to play guidelines
• Perrin (1993) suggests the use of CON to ECC
  ratios traditional
• Hertel (2000 - Sports Med) suggests ECC eversion
  to CON inversion
• Functional ratio Aagaard et al. (1998 - Am J Sp
  Med)

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Isokinetic Strength Discrepancies
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HQ Ratio Comparison between Athletic Groups
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Physiological and Neuromuscular Effects of
Isokinetic Exercise

• Glycolytic, ATP-PC, Krebs Cycle Enhancement
• Motor Unit Recruitment
• Duration of Exercise
• determined by time instead of reps!

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Velocity Spectrum Exercise

• Theories Supporting Usage
• 1) Type I (Slow Twitch) Fibers
• activated at lower velocities
• longer twitch contraction times
• specialized for use at slow velocities
• 2) Type II (Fast Twitch) Fibers
• specialized for high power/high velocity/short
  duration
• 3) Selective Fiber Recruitment vs Variations in
  the Order of Motor Unit Recruitment

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Specificity of Training

• Con vs. Ecc?
• most activities are a combination of both
• Strength Overflow?
• high velocity training is less specific than
  low velocity
• Submaximal Isokinetic Exercise
• if its submax then not isokinetics!!

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Understanding Eccentric Muscle Actions
Implications for the Clinician
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ECCENTRIC

• a person who has an unusual, peculiar, or odd
  personality, set of beliefs, or behavior pattern.
  

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Isometric Muscle Actions

• Muscle creates tension without a change in length
• Max force is created at the end of the ROM
  (review length-tension relationships)
• Peak force MVC (Maximal Voluntary Contraction)
• strength of the muscle without any external load

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Length-Tension Relationships
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Concentric vs. EccentricMuscle Actions

• Concentric
• the muscle develops tension while shortening
• review sliding-filament theory
• Eccentric
• the muscle develops tension while lengthening
• review physiology of eccentric muscle actions

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Sliding-Filament TheoryRevisited

• Resting state lengthened position
• Contracts shortens (concentric)
• Muscle filaments are pulled back creating new
  molecular attachments
• actin and myosin bonds
• ratcheting effect
• requires a tremendous amount of energy (ATP)

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Physiology of Eccentric Muscle Actions

• Review articles by H.E. Huxley (Science, 1969)
  and W.T. Stauber (Exercise and Sport Sciences
  Reviews, 1989)
• Contractile and elastic components of the muscle
  are active
• Force required to break the cross-bridges within
  the sarcomere is greater
• No recycling of bonds (remain in high energy
  state)

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Force Production Differencesbetween Eccentric
and Concentric Muscle Actions

• Differences associated with muscle physiology
• 40 greater force production
• require less energy
• Force-velocity relationships
• traditional curves
• contemporary viewpoint

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Types of Resistance Training

• Isometric
• muscle produces tension without changing length
• Isotonic
• muscle produces tension while changing length
• fixed resistance variable speed
• Isokinetic
• muscle produces tension while changing length
• variable resistance fixed speed

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Advantages and Disadvantages of the Various Types
of Resistance Training

• Isometrics
• Isotonics
• free weights
• variable resistance machines
• Isokinetic
• dynamometers (Biodex Cybex)

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Why are Eccentric Muscle Actions Important?

• Walking
• falling forward interrupted by heel strike
  (knee flexed - quads act eccentrically)
• stance phase - tibia begins to roll-over the foot
  (gastrocnemius fires eccentrically)
• only concentric action during walking is psoas
  firing to flex the hip

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Why are Eccentric Muscle Actions Important?

• Running
• the activity represents stretch and recoil
• toe strike quads absorb elastic energy which is
  then released to contribute to forward momentum
• deceleration phase hamstrings act eccentrically
  to slow the lower leg
• deficient strength strain injury
• foot plant hamstrings reduce forward
  translation of the tibia (unload the ACL)

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Why are Eccentric Muscle Actions Important?

• Throwing Activities
• baseball throw involves 88 eccentric actions
• IROTs are acting eccentrically during the
  wind-up (cocking phase)
• energy recaptured by the stretch and recoil
  mechanism forward momentum of ball
• on follow-through EROTs act eccentrically to
  slow the arm down after release

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Why are Eccentric Muscle Actions Important?

• Jumping Activities
• best example of stretch-recoil mechanism
  (Stretch-Shortening Cycle / Plyometrics)
• quads and calf (gastroc-soleus) act
  eccentrically at foot plant to store energy
  that is released at take-off
• box jumps, depth-jumps, plyos

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Clinical Implications

• Muscle Strength Training
• Isometric
• angle specific gains
• Isotonic
• concentric
• eccentric
• Limiting factors with contemporary variable
  resistance devices
• Research studies indicating eccentric strength
  gains are the greatest

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Clinical Implications

• Muscle Strain Injuries
• M-T junction
• Eccentric muscle actions can occur early in rehab
  because stretch receptors are de-activated
• process called concentric off-loading
• used in patellar and Achilles tendinitis,
  strains, rotator cuff pathologies

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Clinical Implications

• Eccentric over-loading
• used with muscles that statically contract to
  stabilize a joint (shoulder, knee, etc)
• stabilizing muscles counteract the tendency for
  the unstable joint to sublux
• used in the prevention of recurrent MT injuries
• use concept of progressive resistance exercise
  (PREs)
• MT unit is then exposed to functional levels of
  resistance

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Negator Research

• The Negator offers enhanced eccentric isotonic
  exercise in a safe, controlled manner
• Can attach to existing variable resistance
  machines
• No need for assistance by other strength
  professionals

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1RM Percentage Gain
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Negator attached to a Cybex Arm Curl Device
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Negator attached to a Cybex Arm Curl Device
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Negator Counter-Weight Stack
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Negator on Leg Curl Device
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Video of the Negator
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Discussion

• How are you interpreting an isokinetic evaluation
  on muscle endurance by performing multiple
  repetitions of contractions.
• How do you conduct a isokinetic test to determine
  the proportion of fast-twitch muscle fiber for a
  young sprinter.
• What is the importance of isokinetic eccentric
  contraction test to athletes prone to sport
  injury.