Isometric Contraction

by R. Smith

bench press

bench press

Isometric Exercise (Static Exercise)

Isometric contraction is a static form of exercise in which a muscle contracts and produces force without an appreciable change in the length of the muscle and without visible joint motion. Although there is no mechanical work done (force  distance), a measurable amount of tension and force output are produced by the muscle. Sources of resistance for isometric contraction include holding against a force applied manually, holding a weight in a particular position, maintaining a position against the resistance of body weight, or pushing or pulling an immovable object.

During the 1950s and 1960s, isometric resistance
training became popular as an alternative to dynamic resistance exercise and initially was thought to be a more effective and efficient method of muscle strengthening. Based on the early research it was reported that isometric strength gains of 5% per week occurred when healthy subjects performed a single, near-maximal isometric contraction everyday over a 6-week period. Although replications of this study refuted some of the original findings, particularly the rapid rate of strength gain, additional studies during the 1960s showed that repetitive isometric contractions (a set of 20 per day) held for 6 seconds each against near-maximal resistance consistently improved isometric
strength. A cross-exercise effect (a limited increase in strength of the contralateral, un exercised muscle group), as the result of transfer of training, has also been observed with maximum isometric training. Each of these early investigations concluded that isometric training
was a viable means of improving muscle strength.

Rationale for Use of Isometric Exercise

• To prevent or minimize muscle atrophy when joint
movement is not possible owing to external immobilization(casts, splints, skeletal traction)
• To activate muscles (facilitate muscle firing) to begin to re-establish neuromuscular control but protect healing tissues when joint movement is not advisable after soft tissue injury or surgery
• To develop postural or joint stability
• To improve muscle strength when use of dynamic resistance exercise could compromise joint integrity or cause joint pain
• To develop static muscle strength at particular points in the ROM consistent with specific task-related needs

Types of Isometric Exercise

Several forms of isometric exercise with varying degrees of resistance and intensity of muscle contractions serve different purposes during successive phases of rehabilitation. All but one type (muscle setting) incorporate some form of
significant resistance and therefore are used to improve static strength or develop sustained muscular control(endurance). Because no appreciable resistance is applied, muscle setting technically is not a form of resistance exercise but is included in this discussion to show a continuum of isometric exercise that can be used for multifaceted goals in a rehabilitation program.

Muscle-setting exercises Setting exercises involve low intensity isometric contractions performed against little to no resistance. They are used to decrease muscle pain and spasm and to promote relaxation and circulation after injury to soft tissues during the acute stage of healing. Two common examples of muscle setting are of the quadriceps and gluteal muscles. Because muscle setting is performed against no appreciable
resistance, it does not improve muscle strength
except in very weak muscles. However, setting exercises can retard muscle atrophy and maintain mobility between muscle fibers when immobilization of a muscle is necessary to protect healing tissues during the very early phase of rehabilitation.

Stabilization exercises This form of isometric exercise is used to develop a submaximal but sustained level of cocontraction to improve postural stability or dynamic stability of a joint by means of mid-range isometric contractions
against resistance in antigravity positions and in weight bearing postures if weight bearing is permissible. Body weight or manual resistance often are the sources of resistance. Variations terms are used to describe stabilization exercises. They include rhythmic stabilization and alternating isometrics, two techniques associated with proprioceptive neuromuscular facilitation (PNF). Stabilization exercises that focus on
trunk/postural control include dynamic, core, and segmental stabilization exercises.

Multiple-angle isometrics This term refers to a system of isometric exercise where resistance is applied, manually ornmechanically, at multiple joint positions within the available ROM. This approach is used when the goal of exercise
is to improve strength throughout the ROM when joint motion is permissible but dynamic resistance exercise is painful or inadvisable.

Effective use of isometric exercise in a resistance training program is founded on an understanding of its characteristics and its limitations.

Intensity of muscle contraction The amount of tension that can be generated during an isometric muscle contraction depends in part on joint position and the length of the muscle at the time of contraction. It is sufficient to use an exercise intensity (load) of 60% to 80% of a muscle’s force-developing capacity to improve strength. Therefore, the amount of resistance against which the muscle is able to hold varies and needs to be adjusted at different points in the range. Resistance must be progressively
increased to continue to overload the muscle as it becomes stronger.

Duration of muscle activation To achieve adaptive changes in static muscle performance, an isometric contraction should be held for 6 seconds and no more than 10 seconds because muscle fatigue develops rapidly. This allows sufficient time for peak tension to develop and for metabolic changes to occur in the muscle. A 10-second contraction allows a 2-second rise time, a 6-second hold time, and a 2-second fall time.

Repetitive contractions Use of repetitive contractions, held for 6 to 10 seconds each, decreases muscle cramping and increases the effectiveness of the isometric regimen.

Joint angle and mode specificity Gains in muscle strength occur only at or closely adjacent to the training angle. Physiological overflow is minimal, occurring no more than 10 in either direction in the ROM from the training angle. Therefore, when performing multiple angle
isometrics, resistance at four to six points in the ROM is usually recommended. Isometric resistance training is also mode-specific. It increases static strength but has little to no impact on dynamic strength (concentric or

P R E C A U T I O N S : To avoid potential injury to the contracting muscle, apply and release the resistance gradually. This helps to grade the muscle tension and ensures that the muscle contraction is pain-free. It also minimizes the risk of uncontrolled joint movement. Breath-holding commonly occurs during isometric exercise, particularly when performed against substantial resistance. This is likely to cause a pressor response as the result of the Valsalva maneuver, causing a rapid increase in blood pressure. Rhythmic breathing, emphasizing exhalation during the contraction, should always be performed during isometric exercise to minimize this response.

C O N T R A I N D I C A T I O N : High-intensity isometric exercises may be contraindicated for patients with a history of cardiac or vascular disorders.

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