Isometric vs Isotonic vs Isokinetic – Occupational Therapy Foundations of Practice

Root word meanings

• Isometric – same length for muscles.
• Isotonic – same tension.
• Isokinetic – same speed throughout the movement.

Isometric

In isometric exercises, the muscles do not shorten or lengthen. These exercises are often referred to as static. For example, a person may hold a plank position and therefore no muscles shorten or lengthen. Other isometric exercise examples are abdominal vacuums and bridges.

Isometric exercises can help to maintain strength, and to a lesser degree, help to build strength. One limitation to isometric exercises is that it improves strength in only one particular position – the exercise that the person performs itself. Isometric exercises also do not improve speed. However, they can be still useful for enhancing overall stability in the position.

In occupational therapy, one notable measurement of isometric effort is with dynamometers for grip strength, e.g., Jamar dynamometer.^[1]Clerke, A., & Clerke, J. (2001). A literature review of the effect of handedness on isometric grip strength differences of the left and right hands. The American Journal of Occupational Therapy, … Reference List Handgrip strength has been shown to be an outcome predictor of health including nutritional status^[2]Norman, K., Stobäus, N., Gonzalez, M. C., Schulzke, J. D., & Pirlich, M. (2011). Hand grip strength: outcome predictor and marker of nutritional status. Clinical nutrition, 30(2), 135-142., prognosis, quality of life,^[3]Musalek, C., & Kirchengast, S. (2017). Grip strength as an indicator of health-related quality of life in old age—a pilot study. International journal of environmental research and public … Reference List and overall health.^[4]Wind, A. E., Takken, T., Helders, P. J., & Engelbert, R. H. (2010). Is grip strength a predictor for total muscle strength in healthy children, adolescents, and young adults?. European journal of … Reference List

Isotonic

With isotonic exercises, the same amount of muscle tension or weight is maintained throughout the movement. An example is performing a bicep curl as the weight remains the same as the joint moves through the entire range of motion. Other examples of isotonic exercises include push-ups, pull-ups, and squats. The weight of the body remains the same as the joint moves between the start and end ranges.

Isotonic exercises for occupational therapy practice can therefore help to build strength. Strength can enable participation in meaningful activities with function. Strength may be especially important as patients may decondition and lose strength due to an injury or disease such as from even a brief stay in the hospital. According to research, bed rest can result in muscle atrophy at 12% a rate, or an average of 2% per day!^[5]Jiricka, M.K. (2008) Activity tolerance and fatigue pathophysiology: concepts of altered health states. In: Porth, C.M. (ed) Essentials of Pathophysiology: Concepts of Altered Health States. … Reference List

Isokinetic

Isokinetic exercise involves motion, but the speed stays the same, such as with a stationary bike. The word isokinetic contains kinetic, which means motion. With a stationary bike, the leg moves through the circular motion of the pedal circumferences, but the speed of limb motion and revolutions per minute stays the same. In isokinetic exercises, the resistance can vary, such as using the resistance adjustment in an exercise bike. Often specialized equipment is used to promote isokinetic exercise. Another example is a treadmill. This allows target speeds and resistance to be adjusted and dialed in for the individual. Even allows specific muscle groups to be targeted. Overall, isokinetic exercises can help to improve muscular strength and endurance.

In occupational therapy, isokinetic exercises can be used for recovery, to prevent injury, increase flexibility, muscle development, and promote function. Isokinetic machines can be used after an injury or condition such as stroke. Isokinetic exercises also can help to address balance and coordination through improving support of core muscles as well as the spine. This helps patients to build confidence in their recovery and feel empowered in their independence for their participation in occupations even outside of the exercise realm in mobility, work, school, play, and leisure.

Isokinetic exercise is relatively safe as patients do not need to overcome an initial amount of inertia (getting things going from a stop). It is also safe for people with injuries as most machines are self-contained without risk of injuries such as free weights being dropped. In terms of contradictions, one thing to be aware of is the patient’s cardiopulmonary function, MET levels and cardiac rehab phase, symptomatology, chief complaint, and presentation. Patients should follow best practices for exercise including warm-up, staying hydrated, and staying alert.

Which Exercise to Use

Overall, each type of exercise – isometric, isotonic, and isokinetic has its benefits. While we often appreciate a bottom-up understanding of the terminology and physiology, patients likely would may benefit from a combined approach of these exercises based on their needs. A tailored exercise program that targets weaknesses, but also promotes overall health and function from a top-down perspective may also be beneficial. Depending on what equipment you have available to you in your practice, there may be pragmatic limitations, but patients can find creative uses to engage in these exercises with their body alone and some creativity.