Transcript Isokinetics in Rehabilitation

Isokinetics in
Rehabilitation
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!
Isotonic vs. Isokinetic Exercise
Advantages
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1) isolate weak muscle groups
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2) work maximally throughout ROM
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3) velocities simulate functional activity?
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4) inherent safety mechanism
Disadvantages
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1) cost
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2) open-chain motions
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3) cardinal planes
Terminology
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1) force - when a stimulated muscle acts against
a resistance force is produced
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2) torque - F x D (from fulcrum or axis of
rotation)
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3) work - applied force times distance of
rotation
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4) power - time required to perform work
Normal Torque Curve
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1) Angle Specific Torque (AST) -
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2) Peak Torque (PT) -
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3) Average Torque (AT) - torque over entire
ROM
- lower than PT, higher reliability
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Isokinetic Curves
Isokinetic Curves
Power Curves
Abnormal Torque Curve
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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
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Passive - primary function
is the dissipation of energy
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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
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Kin Com, Biodex, Cybex
Instrumentation
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Mode of Muscle Action
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con/ecc
isometric
passive
Test Velocity
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0/s - 1000  /s
above 300  /s difficulty
generating force (not
isokinetics!!)
Principles of Isokinetic
Strength Assessment
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1) Musculoskeletal and CV. Screening
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2) Pt. Education/Familiarization
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3) Stabilization/Joint Alignment
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4) Gravity Correction
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5) Test Velocity
Gravity Correction
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Must be performed during
any gravity dependent joint
testing position
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GC value + to force ?
GC value (-) to force ?
some dynamometers
perform this either
dynamically or stationary
Failure to GC results in:
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quads under predicted
hams over predicted
Confounding Factors to Accurate
Isokinetic Evaluation
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Assess strength not PAIN!
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Joint effusion (neuro-inhibitory effect)
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Muscle co-activation (hams contract near
terminal ROM with knee extension may effect
AT!)
Test Protocols
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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
Interpreting an
Isokinetic Evaluation
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1) Torque, Power, Work - all have high r values
- AT more reflective of pt’s capability to
generate force thru ROM
2) Muscle Endurance 3) F-V Relationships - differences con vs. ecc
Factors affecting muscular force
generation
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Force-velocity
relationship
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concentric
Factors affecting muscular force
generation
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Force-velocity
relationship
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Concentric/eccentric
F-V R Curve – Knee Flex & Ext
FV-R Ankle Eversion
Interpreting an
Isokinetic Evaluation
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Force/Torque ratios Relative to BW 
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Nm torque/kg BW
mainly involving the lower extremity
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Bilateral Muscle Group Comparisons
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Reciprocal Muscle Group Comparisons
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Knee flex/ext (H:Q) = .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
E (CON) : I (ECC) Ratios
in the Ankle
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Trend is for ratios to be < 1.0 why?
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ECC strength values in the denominator will in most
cases be greater than the CON values found in the
numerator
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 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
E (ECC) : I (CON) Ratios
in the Ankle
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Trend is for ratios to be > 1.0 why?
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ECC strength values in the numerator will in most cases
be greater than the CON values found in the
denominator
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 40% greater force production ECC
Interesting to note that at the higher velocity (120°/sec)
that the ratios are elevated
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ECC force production in the ankle typically rises from the slower
velocities to peak around 120°/sec
Implications
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Normative values are needed to allow for
meaningful comparisons
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Will prove useful for clinician:
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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
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“Functional” ratio Aagaard et al. (1998 - Am J Sp Med)
Isokinetic Strength Discrepancies
H:Q Ratio Comparison between
Athletic Groups
Physiological and Neuromuscular
Effects of Isokinetic Exercise
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Glycolytic, ATP-PC, Krebs Cycle Enhancement
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Motor Unit Recruitment
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Duration of Exercise
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determined by time instead of reps!
Velocity Spectrum Exercise
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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
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Con vs. Ecc?
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Strength Overflow?
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most activities are a combination of both
high velocity training is “less specific” than low
velocity
Submaximal Isokinetic Exercise
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if it’s submax then not isokinetics!!
Understanding
Eccentric
Muscle Actions:
Implications for the
Clinician
“ECCENTRIC”
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a person who has an
unusual, peculiar, or
odd personality, set of
beliefs, or behavior
pattern.
Isometric Muscle Actions
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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)
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strength of the muscle without any external load
Length-Tension Relationships
Concentric vs. Eccentric
Muscle Actions
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Concentric
the muscle develops tension while shortening
 review sliding-filament theory
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Eccentric
the muscle develops tension while lengthening
 review physiology of eccentric muscle actions
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Sliding-Filament Theory
Revisited
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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
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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)
Force Production Differences
between Eccentric and
Concentric Muscle Actions
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Differences associated with muscle
physiology
40% greater force production
 require less energy
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Force-velocity relationships
traditional curves
 contemporary viewpoint
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Types of Resistance Training
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Isometric
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muscle produces tension without changing length
Isotonic
muscle produces tension while changing length
 fixed resistance & variable speed
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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
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Isometrics
Isotonics
free weights
 variable resistance machines
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Isokinetic
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dynamometers (Biodex® & Cybex®)
Why are Eccentric Muscle
Actions Important?
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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?
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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
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deficient strength = strain injury
“foot plant” hamstrings reduce forward
translation of the tibia (unload the ACL)
Why are Eccentric Muscle
Actions Important?
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Throwing Activities:
baseball throw involves 88% eccentric actions
 IROT’s are acting eccentrically during the windup (“cocking phase”)
 energy recaptured by the “stretch and recoil”
mechanism = forward momentum of ball
 on “follow-through” EROT’s act eccentrically to
slow the arm down after release
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Why are Eccentric Muscle
Actions Important?
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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, plyo’s
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Clinical Implications
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Muscle Strength Training
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Isometric
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angle specific gains
Isotonic
concentric
 eccentric
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Limiting factors with contemporary variable
resistance devices
 Research studies indicating eccentric strength
gains are the greatest
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Clinical Implications
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Muscle Strain Injuries:
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M-T junction
Eccentric muscle actions can occur early in
rehab because stretch receptors are deactivated
process called concentric “off-loading”
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used in patellar and Achilles tendinitis, strains,
rotator cuff pathologies
Clinical Implications
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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
(PRE’s)
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MT unit is then exposed to functional levels of
resistance
Negator™ Research
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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
1RM Percentage Gain
Control
Concentric
Eccentric
35%
Strength Gain
30%
25%
20%
15%
10%
5%
0%
Groups
Negator™ attached to a Cybex
Arm Curl Device
Negator™ attached to a Cybex
Arm Curl Device
Negator™ Counter-Weight
Stack
Negator on Leg Curl Device
Video of the Negator
Discussion
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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.