Lost on the proper way to practice
So I know that you need to practice slow and consistency is good but I feel like I'm very inefficient with my practice. If you have several trouble passages in a concerto, are you supposed to go over them slow and perfect them all everyday? I feel like if you focus on one then focus on another the next day you're going to lose what you did on the first passage. Right now, it takes me one practice session just to work on my concerto because I just keep doing slow practice and gradually upping the tempo but I'm afraid to lose what I did if I skip that passage the next day. Am I going about this all wrong?
I can't relate to your problem. Muscle memory is a thing, but so is muscle conditioning.
Maybe your concerto is too hard of a piece for you? Did your teacher assign it to you, or did you choose it for yourself? Also when you do slow practice to bring up the tempo of something gradually, you want to take very short sections. A few measures is better than half a page.
Wouldn't it be nice if there was funding to find effective practice technique. Well, high school sports has that kind of funding. They found that students learn a physical technique best (quickly with good retention) when they cycle randomly through roughly 3 minute sessions on various motions. So do 3 minutes on 1 difficult short passage, then another, then another. Eventually, cycle back and do them in a different random order. I've done this and it works.
Funding to find effective practice technique?
Unless you are old enough or sick enough that your body is becoming unreliable and is failing you, I recommend what worked for me over the years:
Sudar, I think Scott pretty much said it. What I might add to it is this:
I would say everyone has given great advice. Also, I strongly advise you to take mental breaks when your practice begins to fail because you run out of mental energy. This is also a good way to prevent injury.
Here's a tip if you are working on a concert piece. Take excerpts from your concerto and construct your own exercises around passages that you want to work on the most. It works like a charm. You might take long notes, for instance, and divide them into eighths, or sixteenths, or other variations, like slurred or separate bowings,always incorporating that byte, or a variation of it, that you want to master. You can even reverse the process. Also, if a lot of shifting is required, be sure to add those shifts into your hand-crafted exercise. Sometimes you may even come up with a cadenza for your piece! You can take that passage and weave, easily, one, or two pages out of it. That's what they did before method books. They would create their own exercises based on the things they wanted to perform in public.