Building up your strength takes time, practice, commitment and patience.
In truth, you may not even realise it is happening.
Internal arts training is not strenuous or stressful.
You undertake regular training and let the mild exercise build up layers of strength.

An hour of training every morning mounts up over time.
Pretty soon you have a level of strength you never expected.
This is not the strength required to lift a massive weight.
It is the strength to deliver a penetrating strike, snap a limb or flip an opponent without trying.