Factors Progression
Intensity (exercise load)
Body position (nonweight- or weight-bearing)
Repetitions and sets Frequency
Type of muscle contraction
Range of motion
Plane of movement Speed of movement Neuromuscular control Functional movement patterns
Submaximal→ maximal (or near-maximal) intensity Low load → high load
Variable: depending on pathology and impairments, weight-bearing restrictions (pain, swelling, instability) and goals of the
rehabilitation program Low volume → high volume
Variable: depends on intensity and volume of exercise Static→ dynamic
Concentric and eccentric: variable progression Short arc → full arc
Stable portion of range → unstable portion of range Uniplanar→ multiplanar
Slow → fast velocities Proximal → distal control Simple→ complex Single joint → multijoint
Stabilization exercises. This form of isometric exercise is
used to develop a submaximal but sustained level of co- contraction to improve postural stability or dynamic stabili- ty 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.196Body
weight or manual resistance often are the sources of resist- ance. Variations terms are used to describe stabilization exercises. They include rhythmic stabilization and alter-
nating isometrics, two techniques associated with proprio-
ceptive neuromuscular facilitation (PNF) described later in the chapter.269,296Stabilization exercises that focus on
trunk/postural control include dynamic, core, and segmen-
tal stabilization exercises, described in Chapter 16.37,228
Multiple-angle isometrics. This term refers to a system of
isometric exercise where resistance is applied, manually or mechanically, at multiple joint positions within the avail- able ROM.55This approach is used when the goal of exer-
cise is to improve strength throughout the ROM when joint motion is permissible but dynamic resistance exercise is painful or inadvisable.
Characteristics and Effects of Isometric Training
Effective use of isometric exercise in a resistance training program is founded on an understanding of its characteris- tics and its limitations.
Intensity of muscle contraction. The amount of tension
that can be generated during an isometric muscle contrac- tion depends in part on joint position and the length of the muscle at the time of contraction.139,293It is sufficient to
use an exercise intensity (load) of 60% to 80% of a mus- cle’s force-developing capacity to improve strength.162,293
Therefore, the amount of resistance against which the mus- cle is able to hold varies and needs to be adjusted at differ- ent 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 con- traction 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.132,193A
10-second contraction allows a 2-second rise time, a 6-second hold time, and a 2-second fall time.55
Repetitive contractions. Use of repetitive contractions,
held for 6 to 10 seconds each, decreases muscle cramping and increases the effectiveness of the isometric regi- men.55,185
Joint angle and mode specificity. Gains in muscle strength
occur only at or closely adjacent to the training
angle.161,162,293Physiological overflow is minimal, occur-
ring no more than 10 in either direction in the ROM from the training angle.162Therefore, when performing multiple-
angle isometrics, resistance at four to six points in the ROM is usually recommended. Isometric resistance train- ty of joints is achieved by activating and maintaining a low
level of co-contraction, that is, concurrent isometric con- tractions of antagonist muscles that surround joints.196The
importance of isometric strength and endurance in the elbow, wrist, and finger musculature, for example, is apparent when a person holds and carries a heavy object for an extended period of time.
With these examples in mind, there can be no doubt that isometric exercises are an important part of a rehabili- tation program designed to improve functional abilities. The rationale and indications for isometric exercise in rehabilitation are summarized in Box 6.7.
Types of Isometric Exercise
Several forms of isometric exercise with varying degrees of resistance and intensity of muscle contractions serve differ- ent 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 exer- cise 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 appre- ciable 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 neces- sary to protect healing tissues during the very early phase of rehabilitation.
BOX 6.7 Isometric Exercise: Rationale and Indications
•To prevent or minimize muscle atrophy when joint movement is not possible owing to external immobiliza- tion (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 resist- ance 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
ing is also mode-specific. It increases static strength but has little to no impact on dynamic strength (concentric or eccentric).172
P R E C A U T I O N S : To avoid potential injury to the con- tracting 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 pres- sure.94Rhythmic breathing, emphasizing exhalation during
the contraction, should always be performed during isomet- ric 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.