There is no such thing as a weak fourth finger. There is only poor leverage. If you are striving to strengthen your hand, I suggest strength isn't the problem. You could be giving yourself an unnecessary headache.

Go to Alan Fraser's Craft of Piano website and try this exercise invented by Franz Liszt: Bicycle Spokes Exercise.

The exercise is didactic in purpose. When you play,  you aren't going to leave your fingers immobile and you aren't going to activate them solely by moving your forearm. The intention here is to illustrate the solidity of playing on your skeleton by lining up the bones.

Give it a try,and if it helps you, I recommend Alan's books. (This is an unsolicited endorsement.)

The proof lies in how it works for you. For inspiration, check out Horowitz playing Scriabin in his concert in Moscow. Bless his heart, he's 83 and when he stands he's feeble. Not so, sitting at the piano! Formidable hand structure with skeletal alignment affords him the power to break strings were he to unleash it fully.

I like to participate in the piano technique forum at Alan Fraser's The Craft of Piano Playing. I recently shared a tip I learned from Steven De Groote for fingering parallel scales.
Steven liked to finger parallel scales so that the thumbs play together. The big problems in scales are to get them smooth, without bumps, and to keep the hands perfectly together. The turn over/turn under in scale playing is hard. If you align the fingering to play both thumbs together, it gives you a little more of a fighting chance to smooth that out.

In the traditional fingering of a B-flat major scale there is no meeting point of the thumbs. However, you can make the thumbs meet if you wish to. In a parallel B-flat major scale, Steven would put his left thumb on C and F. 

C major would have the left thumb on C and F, D major on D and G, etc. This isn't dogma. It's just a choice if you have a passage that has a long parallel scale or even a fragment that could benefit from getting the thumbs together. 

It's not traditional. I don't teach children, and I don't know when it would be appropriate to introduce them to such an idea. I learned that in college. 

It's another choice. Maybe someone else will like it, too.