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 the prefix "iso" (same) with "metric" (distance), meaning that in these exercises the length of the muscle does not change.
Resistance to isometric contractions can involve maximal contractions of the muscle against the body's own muscle (i.e. pressing the palms together in front of the body) or structural items (e.g. pushing against a door frame), but can also involve holding a joint position against a sub-maximal contraction (e.g. holding a resistance band in a fixed position).
A concentric contraction is a type of muscle contraction in which the muscles shorten while generating force.
During a concentric contraction, a muscle is stimulated to contract according to the sliding filament mechanism . This occurs throughout the length of the muscle, generating force at the musculo-tendinous junction , causing the muscle to shorten and changing the angle of the joint.
For example, a concentric contraction of the biceps would cause the arm to bend at the elbow (a biceps curl ).
Exercise featuring a heavy eccentric load can actually support a greater weight (muscles are approximately 10% stronger during eccentric contractions than during concentric contractions) and also results in greater muscular damage and delayed onset muscle soreness one to two days after training.
Technique of combining Passive Stretching and Isometric Stretching in order to achieve maximum static flexibility.
PNF was initially developed as a method of rehabilitating stroke victims.
PNF refers to any of several post-isometric relaxation stretching techniques in which a muscle group is passively stretched, then contracts isometrically against resistance while in the stretched position, and then is passively stretched again through the resulting increased range of motion.
First, the relaxed muscle is stretched by an external force, such as an exercise partner, or by ones own body weight against the floor, a wall, or similar resistance.
At the point, where no further stretching seems possible, the stretch is held for up to 30 seconds . However, during this period, the muscle should be contracted as much as possible. (In the drawing on the right, this is done by trying to press the feet into the floor.)
Finally, when the muscle gets relaxed again, it should be immediately stretched farther, which is then easily possible again.