Download Isokinetic Dynamometry

Isokinetic Dynamometry
Dynamometry is the measurement of force or power. Strength is the ability of muscles to
produce force. Since measuring individual muscle forces are difficult to do directly, operationally
strength is considered the amount of external force produced by a muscle or muscle group during
an isometric contraction. It is quantified by force or better, moment of force, produced by a
single, isometric, maximum voluntary contraction (MVC).
Power is the rate of doing work. For a muscle contraction, power is the ability of a muscle
to do work quickly. At the muscle tendon level, it is measured by taking the product of the rate of
muscle shortening or lengthening times the muscle force. Again, this is a difficult measure to
obtain. Functionally, muscle power is measured by dynamometers capable of measuring force
dynamically while simultaneously measuring or controlling the velocity of the movement.
Isokinetic dynamometers, such as the KinCom and Cybex, do this by controlling the velocity of
the movement and measuring, via a strain gauge force transducer, the force applied. Only the
KinCom can measure both concentric and eccentric contractions, as well as, isometric
contractions and a special type of isotonic contraction.
Length-tension relationship -relationship between the maximum tension in a muscle versus its
length
Force-velocity relationship -relationship between the maximum instantaneous tension in a
muscle versus its instantaneous velocity (concentric portion is based upon Hill’s equation)
Types of muscle contractions:
Isometric -(a) constant length or static contraction or (b) zero velocity of shortening
Isotonic -constant load (a) in vitro, (b) weight lifting or (c) computer controlled
Isokinetic -same as isovelocity
Isovelocity -(a) constant angular velocity or (b) constant rate of shortening
Concentric -muscle shortening or positive work
Eccentric -muscle lengthening or negative work
Equipment:
KinCom 500H isokinetic dynamometer
1.
Safety features. The demonstrator will set up the KinCom to measure knee extension.
Test the safety shut-off switch. Set hardware stops at the ends of the range of motion to
prevent hyperextension and hyperflexion. Use “training” mode to show how software
stops are set.
2.
Passive mode. Set the KinCom to move the limb passively through the full range of knee
flexion/extension. Use a speed of 45 deg/s.
3.
Isometric contractions. Set the KinCom to measure maximum isometric moment of force
(strength) at knee angles of 50, 80, 110, 140 and 170 deg and at hip angles of 90 and
180 deg, approximately. Plot the results of the peak moments versus knee joint angle and
explain the physiological and biomechanical reasons for the different moments of force.
1
2
Hip angle=180
Hip angle=90
Knee angle:
50
80
110
140
170
4.
Isokinetic contractions. Measure another subject’s maximum moments and powers
during concentric and eccentric contractions of the knee flexors and extensors. Use four
speeds; 60, 120, 180 and 240 deg/s. Use the averaging features to average at least three
trials for each condition. Explain the causes of differences among the various conditions
(speed and concentric/eccentric). Plot the results of the peak moments versus angular
velocity and explain the physiological and biomechanical reasons for the different moments
of force.
Joint speed
(deg/s)
Concentric
Moment
(N.m)
Concentric
Power
(W)
Eccentric
Moment
(N.m)
Eccentric
Power
(W)
60
120
180
240
5.
Isotonic contractions. (If time permits.) Reset the KinCom to measure forearm
flexion/extension. Using a third subject attempt to produce an isotonic contraction where
the subject produces a motion with constant moment of force plus or minus 10%.
6.
To view the results with BioProc2 use the Results section of the program, select the data,
then press the 3. Statistics button followed by the 1. ASCII dump. Finally, select File, then
enter a filename with the extension, “.CHX”