The Basic Intensity Variant Explained

In the majority of cases, strength training is carried out in the "Basic" intensity variantThe training weight is moved 6 - 10 times in a 3-2-3-2 rhythm (concentric - isometric shortened - eccentric - isometric stretched).

This results in a time under tension of 60'' - 100''. The exercise ends once no anatomically correct movement can be performed through the full range of motion any more (muscle failure).

Terminology

concentric

A muscle contraction is called concentric 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 physical terms 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 leads to changes in tension and to a lengthening/stretching of the muscles. This form of loading, or contraction, occurs for example when walking downhill, in the front thigh muscle (M. quadriceps femoris).Source: update Fitness training concept and Wikipedia on muscle contraction