Doing these two things has worked extremely well for me:
1) Doing deadlifts. This is a strength-training exercise: https://www.youtube.com/watch?v=4AObAU-EcYE
2) Seeing a good chiropractor about twice a month. (You might need to shop around - I can elaborate on how to select a quality one if people want)
You asked about an app. I actually corrected my earlier posture and lower-back problems using the above and not any kind of app to remind myself to get up and move around; the above helped even though I routinely sat 1-2 hours at a time, in a deep coding trance, without moving around. Recently, though, I started using BreakTime (a macOS app) to remind me to look away from the screen, mainly because I believe it's healthier for my eyes. This is a $5 app I've been quite happy with.
All the above is in the anecdotal "works for me" category. Good luck in your effort to find what works best for you!
Edit: The video link above gives a rough sense of the exercise, but the fine details matter greatly, so if you decide to do it I highly recommend studying the relevant chapter of this book: https://www.amazon.com/dp/0982522738/
Edit 2: More about chiropractors: Few are MDs; the ones I've worked with all went through a 4-year, post-bachelors program. In my experience, chiropractors fit on a spectrum, going from ambulance-chasing quacks to gifted, remarkably effective healers. You want the latter. Only way to find out is to pay for about 3 visits; if you and your body are consistently feeling better physically and emotionally by then, you've found a good one. If not, stop, and go find another. So far, the best I've found lean towards alternative medicine (which was really surprising at first... I'm trained as a physicist, and was REALLY skeptical.) Can't say that's a general rule though. Again, all this is my experience; better to get your own experience and evaluate based on that, instead of blindly deciding based on something you read online.
1) Doing deadlifts. This is a strength-training exercise: https://www.youtube.com/watch?v=4AObAU-EcYE
2) Seeing a good chiropractor about twice a month. (You might need to shop around - I can elaborate on how to select a quality one if people want)
You asked about an app. I actually corrected my earlier posture and lower-back problems using the above and not any kind of app to remind myself to get up and move around; the above helped even though I routinely sat 1-2 hours at a time, in a deep coding trance, without moving around. Recently, though, I started using BreakTime (a macOS app) to remind me to look away from the screen, mainly because I believe it's healthier for my eyes. This is a $5 app I've been quite happy with.
All the above is in the anecdotal "works for me" category. Good luck in your effort to find what works best for you!
Edit: The video link above gives a rough sense of the exercise, but the fine details matter greatly, so if you decide to do it I highly recommend studying the relevant chapter of this book: https://www.amazon.com/dp/0982522738/
Edit 2: More about chiropractors: Few are MDs; the ones I've worked with all went through a 4-year, post-bachelors program. In my experience, chiropractors fit on a spectrum, going from ambulance-chasing quacks to gifted, remarkably effective healers. You want the latter. Only way to find out is to pay for about 3 visits; if you and your body are consistently feeling better physically and emotionally by then, you've found a good one. If not, stop, and go find another. So far, the best I've found lean towards alternative medicine (which was really surprising at first... I'm trained as a physicist, and was REALLY skeptical.) Can't say that's a general rule though. Again, all this is my experience; better to get your own experience and evaluate based on that, instead of blindly deciding based on something you read online.