Muscle Health - Strength Testing Using Isokinetic Dynamometer

An isokinetic dynamometer is a device used in sports, medicine, workplace evaluations, and clinical research testing environments to evaluate joint torque. It is capable of testing the strength (torque) and power of different muscle groups and can be adjusted to assess various upper and lower body limb motions. The isokinetic dynamometer isolates the joint of interest, allowing targeted testing of specific muscle groups. Settings can be adjusted to evaluate muscle performance across different speeds and ranges of motion, accommodating isometric, isokinetic, and isotonic (both eccentric and concentric) muscle action. This precise testing method can compare between right and left limbs and identify any injury risk or areas for improvement.

Isokinetic strength assessment is considered the gold standard of sarcopenia research, as the loss of strength and its consequences make sarcopenia an important topic of study. Most sarcopenia studies include measures of strength to test the effects of declines in muscle mass, changes in muscle composition, or specific treatments on muscle strength.

Strength is often evaluated by measuring the force of either static or dynamic muscle contractions. Static muscle contractions involve exerting force on a stationary object without moving the joints. Isometric contractions are commonly used to measure static muscle strength due to their safety and ease of testing. There are various reliable and portable equipment options available for this type of testing.

Isokinetic strength testing is relevant to everyday activities like walking, climbing stairs, pushing, pulling, and carrying objects. Dynamic muscle contraction occurs when the joints move under resistance. Dynamic strength can be measured using the one repetition maximum (1RM) method or an isokinetic dynamometer. The 1RM method involves finding the heaviest weight that can be lifted through a complete range of motion, often using gym weight machines. While safety concerns have been raised, 1RM testing can be performed safely under careful supervision.

A Better Way…

Isokinetic dynamometers allow for the measurement of strength while the limb or joint moves at a defined speed. Most dynamometers can be monitored by computer, enabling the measurement of force data over the entire range of movement. Using a dynamometer also offers a safety advantage over the 1RM method, as both the speed of movement and range of motion can be controlled.

It is important to ensure that differences in strength observed during testing are due to differences in muscle contractile properties, rather than differences in muscle activation. When testing subjects for strength, incomplete recruitment or suboptimal firing of motor units may occur, especially in inactive younger subjects. As a result, significant improvement in strength may be observed less than a week later due to improvements in muscle motor unit activation, rather than muscle hypertrophy. To address this issue, a practice session should be provided before the actual strength testing at a later second session. Retest measures have been shown to be reliable for both younger and older individuals. Regardless of the chosen form of muscle strength testing, utilizing validated technology such as an isokinetic dynamometer is the ideal method to not only identify current strength but also to predict future injury.