Isometric training is a type of exercise style that emphasizes strength training while using specific exercises in which the angle of the joint, and the associated length of the muscle, does not change during “static” contraction of the limb. Thus, isometric training, which is sometimes simply called isometrics, is performed in fixed (static) muscular positions—without any visible movement in the angle of the joint. This static contraction distinguishes itself from dynamic isotonic exercises that use moving (dynamic) positions in the form of concentric or eccentric contractions.
Training isometrically primarily increases the strength of muscles and tendons at the specific angle that the joint is held fixed during a specific exercise. Secondarily, it strengthens muscles and tendons at nearby joint angles, but to a much lesser amount. Isometric training provides general body conditioning. It is used for rehabilitation, where muscles can be strengthened without applying excessive stress on the joints.
Over the years, the popularity of isometric exercises has waxed and waned. It increased in popularity in the mid-20th century when scientific studies showed it helped to increase muscle strength. Italian-American bodybuilder Charles Atlas (born Angelo Siciliano, 1892–1972) began promoting a form of isometric exercises called “Dynamic Tension” in the 1940s. He showed how his exercise method (which used many isometric exercises) could build a strong body even in a 97-lb (44-kg) weakling. Over the next decades, bodybuilders used isometric exercises, as part of a larger workout, to increase their bulk (muscle size). Many organized athletic teams, including college football teams, began using isometric exercises in the 1960s. Today, isometric training is used as a part of an overall exercise program to build stronger muscles. Isometric training is used regularly by mountain climbers, mountain bikers, wrestlers, alpine skiers, gymnasts, horseback riders, and motocross riders. It is also used in the medical community to help rehabilitate older people and anyone who needs to regain strength in injured muscles.
An exercise involving isometric training consists of a muscle of the body resisting something. For instance, that resistance could be the person's own body weight, or it could be an object, such as a wall or a large piece of furniture. When weights are used, the resistance could be in the form of dumbbells, weight machines, or other such equipment.
Isometric exercises are geared to exercise at only one joint angle, so there is generally not a gain (or only a small gain) in strength at other angles. For example, a static bicep exercise held at a joint angle of 25° only increases the strength of the athlete at that angle. Other isometric exercises that exercise at a specific joint angle may also strengthen the muscles at other angles, but only to minor degrees. For instance, an isometric bicep curl performed at 80° increases strength at neighboring joint angles, but to lesser amounts.
The use of isometric-type exercises are thousands of years old. Many ancient forms of exercise, such as yoga and martial arts, incorporate isometric exercises within their programs. The term “isometric” originates from the ancient Greek prefixes of “iso,” which means the same, and “metric,” which stands for distance. The fact that isometric exercises remain constant (fixed) concurs with its origins of “the same distance” or “equal length.” Specifically, it refers to the way the exercise is performed, without lengthening or shortening the muscles during the time tension is on the muscle and tendon.
In the overcoming isometric exercise, sometimes called an “iso press,” the body is pushed or pulled against an immoveable object for a set period. As much force as possible is used to “try” to move the immovable object. An example of this type of isometric training is pressing the hands down on a countertop. By placing maximum resistance on the countertop, the muscles of the arms are exercised. This type of isometric training involves maximal muscle action because the muscles are used to their maximum. Another example is isometric pull-ups, where a person grabs an overhead bar with their hands and pulls the body up toward the bar, holding the position for several seconds (up to 30 seconds). This exercise can be extended by lowering one's body half way down the bar, and holding again for several seconds (again, up to 30 seconds)—what is called an isometric dip.
Yielding (submaximal) and overcoming (maximal) isometric exercises increase isometric strength and conditioning and muscle muscular size (hypertrophy). However, overcoming isometrics are used more for strength, conditioning, and hypertrophy, while yielding isometrics tend to be used more for rehabilitation.
Isometric training also includes stretching. Called stretch range isometric exercises, or iso contract, the technique consists of taking a muscle to its most stretched position (its weakest joint angle within a particular range of motion). This forces the muscle to work as much as possible at holding this position. For instance, a squat is an isometric stretching exercise that would hold the legs parallel to the floor for one minute.
The duration of the isometric hold varies, along with the number of repetitions. A longer duration hold (ten seconds or more) with few repetitions (less than six) can be done. Conversely, a shorter duration hold (two to three seconds) with more repetitions (six to eight) can also be performed. Both strategies increase strength.
It is generally recommended that a person performs isometric training three times per week if strength building is the goal. The most efficient use of isometric exercises (for strength training) is about 15 to 20 maximal isometrics per session with static holds lasting from 3 to 5 seconds. When submaximal exercises are performed, the duration of each should be increased and the number of repetitions decreased. The number and duration of isometric exercises varies depending on the muscle type, athletic sport, fitness level, and other such factors.
People use isometric training to strengthen specific muscles at specific joint angles so they concentrate on only those static exercises. They are usually not interested in exercising at other angles. If they are interested in exercising the same muscle at several joint angles, then the exercises are done at 10- to 30-degree increments.
For rehabilitation of any injury, a medical professional or team of rehabilitation experts should be consulted before starting any such isometric training. For instance, if one injures the rotator cuff (muscles in the shoulder joint), a physical therapist may recommend isometric exercises to strengthen the muscles that stabilize the shoulder.
Warming up is important, as it is with any type of exercise or physical activity, because it helps to prepare the muscles before they are asked to do more strenuous work. Isometric exercises place the muscles under extra tension for longer periods so a warm-up period is critical. A warm-up period may consist of about five minutes of light exercise or walking to let the body get accustomed to exercising. Performance of stretching exercises is recommended during the warm-up period.
Once isometric training is completed, it is a good idea to spend about five minutes cooling down. Light exercise or walking helps the body to settle back down to its normal routine. More stretching exercises are also helpful.
Performing isometric exercises poses some additional health risks to the body. One of the primary risks is to the cardiovascular system, especially the heart. During the time that an isometric exercise is being performed (and one is holding a fixed position of resistance), blood pressure may increase. Individuals at risk or with cardiovascular disease should consult first with their physicians about the appropriateness of performing isometric exercises with their medical conditions.
It is important to breath continuously (and not hold one's breathe) during the performance of isometric exercises. Holding one's breath further increases high blood pressure. As such, isometric exercises may be contraindicated for those with high blood pressure (hypertension) or any type of cardiovascular disease.
As with most exercises, injuries are always possible with isometric training. If weights are used, muscles can be stressed, joints torn, or tissues strained. To minimize the risk of injury during isometric training:
Isometric training is very effective at increasing the strength of the tendon at the specific joint angle being exercised. It is not as good at increasing overall strength for the other joint angles that are not being exercised (within the full range of possible motions); unless these specific angles are also isometrically exercised on a systematic basis. The magnitude of the tension is most important for strengthening and enlarging the muscle. However, duration of the tension is also important. Strengthening of the muscles is maximized with isometric exercises that last less then ten seconds. Increasing the size of muscles (what is called hypertrophy) is maximized when exercising from 10 to 30 seconds. The amount of time is also dependent on the specific muscle group being exercised. Likewise, flexibility is enhanced with the use of isometric training. It is often used in rehabilitation situations because isometric exercises take stress off the connective tissue.
Isometric exercises are performed statically (without movement) as opposed to dynamically (with movement). Consequently, isometric exercises are not suitable for many athletes because they need exercises that strengthen their prime activities, such as running and jumping for gymnasts. Most sports use dynamic movements that are performed at near-maximal and maximal speeds and with little or no resistance. In these cases, isometric training is not appropriate because it does not increase the speed at which the legs sprint, for example. The entire range of movement for the muscle is not exercised, making it least suitable for such dynamic sports. However, isometric training can be used as an effective supplement to dynamic-type training.
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