[How much strength is needed for fitness?].
In order to tolerate the exertion in fitness exercise in the long term a sufficiently strong trunk musculature should be aimed at. In order to stabilize and balance the trunk and the pelvis there should be an optimal interaction of the muscles of the abdomen, the lateral trunk, the back and the flexors and extensors of the hip. If that balance is disrupted, muscular imbalance and a weakening or shortening of the muscles involved can occur. That imbalance leads to inadequate and excessive strain of the functional system of spine and pelvis. The functional anatomy of the trunk is described with clinical references in order to elucidate this context. A program of strength and stretching exercises for the trunk is presented suited to the needs of those practicing fitness exercise.