Isokinetic Dynamometry
- Exercise at a constant velocity (distance/time)
- Torque resistance is proportional to torque applied (Optimal loading of the muscle is able be maintained throughout as because the machine will continuously readjust to match torque applied.
- Technology attempts to adjust for length-tension, force-velocity and moment arm effects across a joint
- Linear (Rarely done) or Angular Force
Isokinetic Uses
- Outcome measures
– Bilateral Comparison
– Pre/Post designs - Training
– Endurance, strength, fatigue - Eccentric Loading (through entire ROM)
- Opposing muscle Group Testing (Ham/Quad Ratio)
Ratios of opposing muscle groups gives you an idea of the…
stability of the joint when maximally contracted
How does this machine make sure not to go past someones ROM or overload the muscle to the point of injury?
- As many fail safes
General Procedure
- Choose Pt body orientation
- Isolate muscles for joint and directions of interest (Align motor’s axis to joint axis; prevent compensation from other muscles-stabilization straps)
- Set range of motion angle stops/brakes
- Set concentric and eccentric angular speeds
- Set number of repetitions
- Exercise trials: set desired torque output goals
This is an example of:
- Active feedback control of how much force is being put into the joint (torque training)
- Considered biofeedback or neuromuscular reeducation
Different speeds correlate to ____ tasks. Things over ____ correspond to things with gait.
- functional
- 60 degrees/sec
Peak Torque
Measurement Variable
- Most accurate and reliable measure, “gold standard”
- As velocity increases, Peak Torque decreases
- Units: Nm or [ lbf·ft ]
- Normalize by BW%
We care about the value of the ____ not so much the degree/angle in which it occurs
- peak torque
Angle Specific Torque
- Allows for you to assess weakness at an angle (less supported by literature)
- As speed changes, so does Peak Torque
Rotational Work
- Area under the torque curve
- Ability to produce torque (light gray) throughout the ROM; Total energy the muscle generates throughout ROM
- Variables Reported
– Total = All reps
– Peak = Peak rep - Units: Joules (J) or ft-lbf
Power
- Torque, distance and time
- torque x ω
- Unit: Joules/sec = Watts (W)
- Variables Reported
– Average = All reps
– Peak = Peak Rep
ω = angular velocity
Power is a commonly used research variable. Why?
- Power is correlated to injury
Peak Torque Acceleration Energy (TAE)
- Greatest work during first 125 ms
- Theory: “Measure of explosiveness”
- Lacks reliability, especially at low speeds
Endurance Index
- Ability of muscles to perform repeated contractions vs load
- Type of Protocols
– Relative Parameters: # of reps to 50% Peak torque (PT) or % decline in PT, work or power; PT, work or power after a # of contractions or time period
– Absolute parameters: total work of last 5 reps or total reps (higher reliability)
Why are absolute measures better than relative?
May be due to the first couple repetitions they didn’t try or weren’t familiar enough to give max effort.
What are some ways to interpret the data we get from the isokinetic dynamometer?
- Databases (Type of Dynamometer, Subjects, less common for Dx)
- Bilateral Comparison (involved/uninvolves or UE vs LE)
- Reciprical muscle group ratios (Ex: Ham/Quad: relationship unclear); Functional ratios, no consensus.
Issues to consider
- Isolation and stabilization (Axis of rotation and ROM)
- Standardization of instructions
- Cognitive - Learning aspect (3-15 Practice reps and Test Reps)
- Gravity Compensation (Effects of gravity, impact on muscle group ratios, plane of motion); Going against gravity is harder; turn on gravity elimination to get true forces
- Machine acceleration and deceleration delay
- Torque overshoot (is it true data?)
Isokinetic exercise involves 3 phases of movement…
- Acceleration, Constant, Deceleration
- Machine has to think and takes time to match torque produced by the person
- Loading range decreases with increases in velocity
If you get data like this what should you do?
Ignore the data before and after that isn’t at constant speed.
Torque Overshoot
- Initial spike followed by oscillations
- Dynamometer reacting to catch up to the performer (dynamometer and PC ~100Hz)
- People kick to fast or are not stapped in well enough
- Adjust data by:
– Damping/filtering to reduced the overshooting
OR
– Only use data from constant velocity periods (called “windowing”)
This is an example of
Damping/filtering torque overshoot
When considering the use of the isokinetic dynamometer what do you need to consider?
- Cost benefit ratio (device set up time for pt)
- Usefulness in treating pt (specificity of training)
Force plate and data capture is becoming more popular for LE/functional
