Isokinetic Assessments of Muscle Function Lab 5 Isokinetic Assessments of Muscle Function

Three most common forms of strength testing Isometric Dynamic constant external resistance (DCER) Isokinetic

Isometric testing It involves the use of a device that measures force output resulting from muscle actions with the body segment in a fixed position. No movement is involved. No mechanical work is performed. Results are specific to the joint angle and are not reflective of force production capabilities for normal movements.

DCER testing Utilizes resistances that are moved through a range of motion by a body segment Indicates only the amount of resistance that can be overcome at the weakest point in the range of motion Does not assess force production capabilities at controlled velocities of movement

Isokinetic testing Involves the use of special equipment that continuously measures and records torques and joint angles as a body segment moves through a range of motion at a preselected velocity controlled by an isokinetic dynamometer Provides force output values for every point throughout the movement and allows for control of velocity for such movements Can be used to estimate fiber type in the exercise muscle group.

Peak torque vs. velocity of movement As velocity of movement increases, peak torque levels tend to decrease during concentric muscle actions due to increased dependency on fast twitch fibers Those who excel in activities requiring high-velocity movements do so, in part, because of an ability to develop high levels of torque during rapid movements.

Peak torque vs. velocity of movement

Peak torque and range of motion Force production capabilities are diminished at the extremes of a full range of motion. This response pattern underscores the inability to apply maximal overload throughout a DCER-type movement.

Torque vs. knee joint angle

Peak torque vs. repetitions With repeated maximal effort muscle actions, torque production declines. Fast twitch fibers tend to become fatigued sooner than slow twitch fibers. Rate at which torque declines during repeated muscle actions reflects, to some degree, the fiber type composition in the exercised muscle group.

Peak torque vs. repetitions

Isokinetic testing formulas Percent Decline = ((Initial Peak Torque – Final Peak Torque) / Initial Peak Torque) x 100 Percent Fast Twitch Fibers = (Percent Decline – 5.2) / 0.9

Isokinetic testing example Initial Peak Torque = 100 Final Peak Torque = 50 Percent Decline = ((100 – 50) / 100) x 100 = 50% Percent Fast Twitch Fibers = (50 – 5.2) / 0.9 = 49.8%