Isometric exercise or isometrics are a type of strength training in which the joint angle and muscle length do not change during contraction (compared to concentric or eccentric contractions, called dynamic/isotonic movements). Isometrics are done in static positions, rather than being dynamic through a range of motion.
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The joint and muscle are either worked against an immovable force (overcoming isometric) or are held in a static position while opposed by resistance (yielding isometric).
An example of this in the context of the bench press would be that a yielding isometric would be holding the bar at a given place even though it could be pressed higher, and an overcoming would be pressing the bar up into the safety guards of a squat cage that prevent pushing the bar any higher.
The distinction is that in a yielding isometric, one is pressing roughly the exact amount of pressure needed to negate the resistance, neither dropping or lifting it. Whereas in an overcoming, one can be exerting more force and simply unable to move it. The yielding wavers slightly into concentric/eccentric actions due to inexact control, whereas the overcoming is more purely isometric and can involve more variation in the force used since one can press harder without the bar moving.
Isometric exercise is a form of exercise involving the static contraction of a muscle without any visible movement in the angle of the joint. This is reflected in the name; the term "isometric" combines Greek the prefixes "iso" (same) with "metric" (distance), meaning that in these exercises the length of the muscle and the angle of the joint do not change, though contraction strength may be varied.[1] This is in contrast to isotonic contractions, in which the contraction strength does not change, though the muscle length and joint angle do.
Resistance in isometric exercises typically involve contractions of the muscle using:
Depending on the goal of the exercise, the exertion can be maximal, or sub-maximal.
Isometric exercises are thousands of years old, with examples from the static holds in certain branches of yoga or Chinese martial arts (kung fu).
Isometrics were first brought to the modern public's attention in the early days of physical culture, the precursor to bodybuilding. Many of the great bodybuilders of the day incorporated isometric exercises into their training regimes.[2] Isometrics fell out of favor as it was discovered that many of the principal advocates were using anabolic steroids to enhance their gains.[3]
Today many new training protocols exist incorporating isometrics once again. Isometric exercises are often made into parts of normal, isotonic exercises. For example, during a set of rows, some people hold their position when the handles are closest to their chest in order to "squeeze" the muscle, in an effort to further strain the muscle.
Contrary to popular opinion, The Charles Atlas "Dynamic Tension" Course did not use any true isometric exercises, but rather Self-Resistance (that is: Pitting one limb against the other) and Calisthenics.
Isometric exercises can also be used at the bedside to differentiate various heart murmurs; the murmur of mitral regurgitation gets louder[4] as compared to the quieter murmur of aortic stenosis.[5]. They can also be used to prevent Disuse Syndrome in a limb that has been immobilized by a cast, following a fracture.
Isometric exercises have some differences in training effect as compared to dynamic exercises. While isometric training increases strength at the specific joint angles of the exercises performed and additional joint angles to a lesser extent, dynamic exercises increase strength throughout the full range of motion.[6] Generally speaking, people who train isometrically don't train through a full range of motion, as the strength gained at the training joint angle is where they require it. While dynamic exercises are slightly better than isometric exercises at enhancing the twitch force of a muscle, isometrics are significantly better than dynamic exercises at increasing maximal strength at the joint angle.[7] Flexibility may be increased when isometrics are performed at joint range of motion extremes. These isometric contractions recruit muscle fibers that are often neglected in some dynamic exercises. For example, gymnasts are extremely strong at great ranges of motion through the practice of isometric holds.
Danger in isometric exercise is primarily attributed to its immediate effects on the cardiovascular system. During an isometric hold, blood pressure rises rapidly, and an overly long hold, or one performed with poor breath control, may result in fainting, stroke, or other injury. However, dynamic exercises present the same problem if heavy weight is used; additionally, dynamic exercises have the problem of changing, irregular demands on strength throughout the motion, and critical moments where the movement cannot stop without losing control over the weight. If control is lost, severe injuries may result; besides the possibility of crushing the body, joints and tissue can be torn. As well, the irregular strength demands can hide flaws(through shifts in balance or "cheating" motions) and can cause uneven development of muscle groups, which adds to the danger over time. Isometric holds, in contrast, do not place demands on form or balance, and will naturally apply the most stress to the weakest parts used in the hold, which leads to a well-rounded development of all joints and muscle groups used in the hold.
Because isometric exercise requires no special equipment or settings, and its techniques are simple and time-efficient, it presents a cheap and accessible alternative to dynamic exercise, (at the cost of being less effective for some fitness goals.)
NASA has researched the use of isometrics in preventing muscle atrophy experienced by astronauts as a result of living in a zero gravity environment. Isometrics, muscle lengthening and muscle shortening exercises were studied and compared. The outcome showed that while all three exercise types did indeed promote muscle growth, isometrics failed to prevent a decrease in the amount of contractile proteins found in the muscle tissue. The result was muscle degradation at a molecular level. As contractile proteins are what cause muscles to contract and give them their physical strength, NASA has concluded that isometrics may not be the best way for astronauts to maintain muscle tissue.[8]
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