In Aikido training, when you practice techniques against each other, a considerable amount of force is applied to the little toe side of the foot, so a large amount of force is also applied to the knees.
Sometimes a practitioner says you have to move your hips.
If you don’t know how to move koshi/tanden, there will be too much power in the knee joint. That is dangerous and should be avoided.
A dangerious example
In the example, the knee is going too much to the outside. The knee and the ball of the foot must be tied tightly. The power coming from the koshi and tanden must follow the line from the groin to the knee and further to the ankle, foot and toes.
The photos are taken from a video clip: KU Quick Tips – Alignment of feet and knees.
Study Group Tomiki Aikido 