My former teacher often demanded of me to practise everything loudly, when learning a new passage, so 'that I could teach the fingers how to play it'. I'm not doing it anymore, because you only get used to practise the passage sounding ugly. Practising is not just about playing the notes in the right order in the right tempo, sound is just as important. In the long run you'll tire your ears by listening to a harsh sound all the time, and when you have mastered the passage, and want to actually make it sound good, you ears are already imune to your own playing. If you want to practise anything in another dynamics than written, find one that is relaxed and comfortable for you. Never force anything for the sake of forcing.
George Kochevitsky suggests in his book "The Art of Piano Playing - A Scientific Approach" that, based on some neurological research, practising extremely softly (like pppp) actually gives you the feeling of strong fingers when you return to the 'real' dynamics. This way of practising is one he recommends rather than practising extremely loudly.
If you really want to have control over what you are doing, practise the difficult bits as soft as you can, connect your finger to the key before depressing it, and go all the way to bottom of the key without pushing. You might need to practise it extremely slowly, but trust me, it helps.
In this way of practising, the essential part is having contact with the key before depressing it. You'll realize how little effort it takes to strike the note, even on the heaviest keyboard!