An isometric exercise (also known as static exercise) is an exercise involving the static contraction of a muscle without any visible movement in the angle of the joint. The term "isometric" combines the Greek words isos (equal) and -metria (measuring), 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. This is in contrast to isotonic contractions, in which the contraction strength does not change, though the muscle length and joint angle do. The three main types of isometric exercise are isometric presses, pulls, and holds. They may be included in a strength training program in order to improve the body's ability to apply power from a static position or, in the case of isometric holds, improve the body's ability to maintain a position for a period of time. Considered as an action, isometric presses are also of fundamental importance to the body's ability to prepare itself to perform immediately subsequent power movements. Such preparation is also known as isometric preload.
Overcoming and yielding isometrics An isometric action is one where the observable angle of the joints is maintained. While this definition always applies there are various sub-definitions which exist in order to emphasise how effort is being applied during specific isometric exercises. In a yielding isometric exercise the ambition is to maintain a particular body position; this may also be called maintaining an isometric hold. In an overcoming isometric exercise the ambition is to push or pull against either another part of the self, which pushes or pulls back with equal force, or to move an immovable object. On this basis, an overcoming isometric may additionally be referred to as being an isometric press or an isometric pull.
Unweighted isometrics In unweighted isometrics the exerciser uses only themselves for resistance. For example, holding a crouched position, or pressing the palms of the hands against each other. Where by the self presses against itself, this is also referred to as self-resistance or Dynamic Tension training.
Weighted isometrics Weighted isometrics involve the additional holding of a weight, and the pressing or pulling of an immovable weight or structure. For example, in a bench press set-up the barbell can be held in a fixed position and neither pushed upwards nor allowed to descend. Alternatively, in a mid-thigh pull set-up, a person can attempt to pull a fixed, immovable bar upwards.
Isometrics in combination with dynamic exercise
Isometric training is rarely used by itself and it is usually incorporated into a wider training regime. For instance, an isometric plank may be incorporated into a plyometrics regime. In addition, when a subject performs a dynamic movement, supportive muscle groups can work isometrically. For example, if a person squats while holding a dumbbell in front of their chest, then their arm action will be relatively isometric, whilst their leg action will be dynamic. Such a relationship between an isometric hold and a dynamic movement is often found in weightlifting: participants commonly hold a barbell overhead with straight arms whilst straightening their legs as they stand up from a squat position. This allows for the legs to be primarily responsible for the lifting of the weight. In most sporting contexts, however, the use of a pure isometric action is rare. In skiing, for example, the skier consistently maintains a crouched position. Whilst this may be considered to be an isometric hold, there is also an amount of dynamic movement as the skier alters how deep the crouch is during their travel. Thus, isometrics can be said to be involved in and supportive of the overall skiing action, even though it is not solely isometric in nature. In weight training and calisthenics, it is often the case that one phase of the exercise is more difficult to perform than others. If the exerciser tends to fail at this point then it is referred to as a sticking point. An isometric hold may be incorporated to strengthen the exerciser's action at this point. For instance, a sticking point in a heavy back squat is usually the lowest position reached. An isometric hold can be adopted in this position in order to strengthen the lifter's ability to hold the weight there. Over a period of training this can help them to lift the weight more easily from this position and thereby eliminate the sticking point.
Isometric presses as preparation The isometric preloading of muscles is instinctively performed in order to generate power to be used in subsequent dynamic movements: a fundamental element of this muscular preloading is the performance of an isometric press action. An everyday example is a person getting up off a chair. They first raise their posterior off the chair and then perform a pressing action downwards on their bent legs. As the bent legs resist the downward force upon them in equal measure, an isometric press is generated. From this point, the person then straightens and stands up. A more dynamic example is a vertical jump. Here, the jumper crouches down and adopts a similar isometric press before powering upwards into the jump. The employment of isometric presses in order to aid explosive power movements is also found in sports such as boxing. Here, the boxer may bend their lead leg, while positioning their torso and its respective bodyweight over it, so there exists equal forces between the upwards force of the bent leg and the downward force of the torso. The boxer then throws a lead hook from this position and the forces from the isometric press are channelled into the punch and help to increase its overall power. Such a channelling of force fundamentally represents the purpose of an isometric preload: which is as a preparatory action to aid a subsequent power movement.
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