Sitting at the organ
An organist requires stability in the upper body, as he or she does not have support from the feet for more short moments while playing. It is thus important to sit with support under a significant area of the thighs. Train by finding stability in the sitting position according to video sitting stability. Both your abdominal muscles and back extensors need to have strength and stamina in order to stabilise the pelvis and trunk of the body while sitting without constant support from the feet.
The contact point between the foot and the pedal should be the inner part of the front of the foot; for this reason, the knees should be held together, and thus a slight inward rotation of the hips is required. When playing certain organs, you may have to hold the thighbones more parallel in order to play with the front of both feet.
When playing on the pedals, most of your movements are directed down into the feet and lower legs. When playing pedals on the left side, your centre of balance will come more to the right buttock, and vice versa; it is important to be able to sit in the same place but change your centre of balance when playing the pedals.
The hand
Please see 3.5 Piano ergonomic and the different videos about Hand exercises
