Muscle contractions ch 7 kin 130

Examples:

The bench press provides another example of these muscle contractions, and does a particularly nice job of showing these contractions in relation to gravity. In the down phase, in which the movement is working with gravity, the contraction is eccentric. In the up phase, in which you are resisting gravity, the contraction is concentric. When there is no change in the muscle length, the contraction is isometric.

Example:

As you can see when performing a bicep curl, the up phase, or flexion, involves a concentric contraction because the muscle in shortening. You can also tell it is a concentric contraction because the movement is going against gravity, as the arm is moving upward, working against the resistance provided by the weight. The down phase, or extension of the bicep curl is an eccentric contraction because the muscle is lengthening as it moves with gravity, slowly giving in to the resistance provided by the hand weight. When the bicep is contracted but is not moving, it is an isometric contraction.

Concentric

Concentric contractions involve the muscle developing active tension as it shortens and occur when the muscle develops enough force to overcome the applied resistance. Concentric contractions may be thought of as causing movement against gravity or resistance and are described as positive contractions. The force developed by the muscle is greater than that of the resistance. This results in the joint angle being changed in the direction of the applied muscular force and causes the body part to move against gravity or external forces. Concentric contractions are used to accelerate the movement of a body segment from a lower speed to a higher speed.

Isotonic

Dynamic, tension remains constant as muscle shortens or lengthens. Isotonic contractions involve the muscle developing tension to either cause or control joint movement. The tension remains constant throughout the joint movement. They may be thought of as dynamic contractions, because the varying degrees of active tension in the muscles are either causing the joint angles to change or controlling the joint angle change that is the result of external forces. A biceps curl would be an example of a isotonic contraction.

Eccentric

Eccentric contractions involve the muscle lengthening under active tension and occur when the muscle gradually lessens in tension to control the descent of the resistance. The weight or resistance may be thought of as overcoming the muscle contraction, but not to the point that the muscle cannot control the descending movement. Eccentric muscle actions control movement with gravity or resistance and are described as negative contractions. The force developed by the muscle is less than that of the resistance, which results in a change on the joint angle in the direction of the resistance or external force, and allows the body part to move with gravity or external forces. Eccentric contractions are used to decelerate the movement of a body segment from a faster speed to a slower speed or stop the movement of a joint already in motion.

Eccentric principles

If the movement is in the direction of the resistance, or toward the pull of gravity, and if the movement is being controlled by muscular effort as the segment gradually moves in the direction of the opposing force, the contraction is eccentric. In this case, the muscles that are primarily responsible for the movement are opposite of those indicated by the action. For example, if you are extending your arm in the down phase of a biceps curl, your flexors are primarily responsible for that movement. This can be a confusing concept as the flexors are opposite of extension, which was the movement. Just remember, if the contraction is concentric, the muscles match the movement, if the contraction is eccentric, the muscles are opposite of the movement.

Concentric principles

In general, gravity is usually the force that is opposing the pull of a muscle. When the movement is opposite to the resistance force, or opposite to the pull of gravity, the contraction will be concentric. If the contraction is concentric, the muscles that are primarily responsible for the movement will be the same as those indicated by the movement. For example, if you are flexing your muscle, the flexors will be primarily responsible for the concentric contraction that is being performed. If the movement is through gravity, meaning that it cuts across the line of pull of gravity, the contraction will always be concentric. For example, if you were swinging a baseball bat, or performing a forehand shot in tennis, you would be moving through gravity, working in the transverse plane. These movements would be primarily controlled by concentric contractions. In this instance, because the contraction is concentric, the muscles will match the action.

Muscle Contractions

It has become increasingly common to refer to the various types of muscle contractions as muscle actions instead. Muscle contractions can be used to cause, control, or prevent joint movement. To elaborate, muscle contractions can be used to initiate or accelerate the movement of a body segment, to slow down or decelerate the movement of a body segment, or to prevent movement of a body segment by external forces. Muscles can shorten, remain the same, or lengthen.

Isokinetics

Maximum muscle effort at the same speed throughout the entire range of motion of the lever. The development of exercise machines has resulted in another type of muscle exercise known as isokinetics. Isokinetics is not another type of contraction, rather it is a specific technique that may use any or all of the different types of contractions discussed previously. Isokinetics is a type of dynamic exercise usually using concentric and/or eccentric muscle contractions in which the speed or velocity of movement is constant and muscular contraction occurs throughout the full range of the movement. Nautilus machines are engineered to allow this type of contraction.

Isometric

Static contractions with no change in the length of the muscle partial or complete contraction, isometric contraction occurs when tension is developed within the muscle but the joint angle remains constant, resulting in no appreciable change in length. Isometric contractions may be thought of as static contractions because a significant amount of active tension may be developed within the muscle to maintain the joint angle in a relatively stable or static position. Isometric contractions may be used to stabilize a body segment to prevent it from being moved by external forces. Performing a wall sit would be an example of an isometric contraction, as there would be no change in the joint angle, once you get yourself into position