In the knee push-up position (knees on the floor, feet held high with toes raised, body forming a straight line from head to knees, hands together under the chest), bend and stretch the arms (lower and raise the upper body).
Attention:
No hollow back and elbows bent at an angle of approx. 45° from the upper body ("A" shape with the arms). Keep your shoulders fixed and pull them down towards your hips.
Lighten:
Lower your upper body less (hardly bend your arms); support your arms on a raised surface.
Harden:
Additional weight (on the back); unstable support for the arms and/or legs; perform normal push-ups without knee support.
Variant:
Vary the position of the hands/arms (e.g. wide, narrow, together).