Iso Contraction: The Intensity Technique Explained

With the Iso Contraction method, the training weight is held statically in the maximally shortened position. Isometric muscle contractions increasingly restrict the energy supply, because the pressure on the blood vessels reduces blood flow to the muscle, and from around 70% of maximum muscle force it stops completely. The training weight also acts on the muscle with the same intensity throughout the entire duration of tension, since the joint angle doesn't change, and so the load on the muscle doesn't change either.

The subsequent reduction of the training resistance fatigues the muscle even further, because the torque it needs to produce decreases. This means further repetitions can be performed.

For single-joint exercises, the training weight is held isometrically at the point of maximum muscle shortening for approximately 60''. For multi-joint exercises, it's held at the point of greatest load on the muscle. At muscle failure, the weight is set down slowly and halved. The exercise is continued immediately (pause max. 3 seconds) at a rhythm of 3-2-3-2 until correct movement through the full range of motion is no longer possible. If more than 10 repetitions are still possible after the reduction, a reduction of a little more than 50% is chosen.

Terminology

concentric

A concentric muscle contraction occurs when a muscle shortens while exerting force – for example, lifting a weight or accelerating an object. In doing so, the muscle performs physical work.

isometric

The force increases while the muscle stays the same length (holding-static). In the physical sense, no work is done, since the distance covered is zero.

eccentric

Here the resistance is greater than the tension in the muscle, so the muscle lengthens (negative-dynamic, yielding); the muscle "brakes" a movement in the process. This causes changes in tension and lengthening/stretching of the muscle. This form of load, or contraction, occurs for example in the front thigh muscles (M. quadriceps femoris) when walking downhill.

Motor unit

A motor unit consists of a single α-motor neuron together with all the muscle fibres it innervates.

Torque

Torque is a physical quantity in classical mechanics. It plays the same role in rotational movement as force does in straight-line movement. A torque can accelerate or slow down the rotation of a body, and twist or bend the body.

Muscle failure

Despite maximum effort, no further movement is possible.

single-joint

A muscle that spans only one joint and moves it.

multi-joint

A muscle that spans several joints and moves them.

Source: update Fitness training concept and Wikipedia