Yoga for Strength isn't about just doing poses to mindlessly get stronger. It is about directing your awareness and your effort so that you can apply strength effectively with less effort.
If you put your effort in the right place, you don't have to use so much of it.
For any strengthening pose the first step is to create stability somewhere within your body.
The better you are at creating stability, the easier it is to get stronger with less effort.
If you are having problems developing strength:
Then you can get stronger with less effort.