Flex AI Workout Trainer & Log

• Free to download
• In-app purchases

Last verified 31 Jul 2026

4.6 2401 ratings · App Store

1. 5/5Great App

   I’ve very often struggled to maintain a consistent workout routine without relying on a trainer. I started using this app to supplement my regular training routine. I’ve used it on days where I just wasn’t sure what to focus on, and it has helped by making it easy to target a specific muscle group or filter by equipment. The smart progression and auto tracking has really helped me see tangible progress in my training. It’s taken a lot of the effort out of planning my workouts, making actually going to the gym much easier and enjoyable. I do like how it is easy to swap out an exercise, or adjust the number of reps or weights on the fly. This has been useful when the gym is busy and I may not have access to the right equipment, it makes it really easy to adapt a workout. The animations and descriptions of what to do in an exercise are also really helpful. I would recommend this to anyone who struggles to track and maintain a consistent workout plan.

   ~(0_0~) ZombieGhost · 31 Jul 2026

2. 5/5Best Workout App for Intermediate and Advanced Training

   I’ve been weight training for about 15 years and one of the biggest keys to success in the gym is consistency workout to workout. Flex is built exactly for this. It allows you to build your own workouts in a simple, easy to use format. There are premade workouts available for beginners but I don't think this is really the app’s strength. It remembers your last weight and set for each exercise and carries it over to the next workout. It tracks your rest (which you can customize) And if you make modifications intra-workout, you can save those for the next time as well. The stats dashboard is helpful for tracking progress, though could use some improvement and more detail. Try it out for free, but if you have an apple watch, you’ll definitely want to pay for it, the logging on the watch has changed my ability to stay focused and keep my phone away while working out. Overall an amazing app if you want a highly customizable, simple interface logging app that doesn't push a specific training style or set of workouts.

   XJRGU25 · 31 Jul 2026

3. 4/5Good for detailed tracking

   Great for saving workouts whether these are cardio, calisthenics, or strength training. The app has a bank of exercises to choose from and if needed, you can create custom ones. You can group exercises into supersets and set rest times between reps. Also, if competition and point systems motivate you to exercise, then this app is for you! You earn points for every workout and can unlock achievements for more points. If you really want to unleash your competitiveness, view the rankings. It’ll really humble you. I left off a star because it’d be more convenient if I could add workouts anytime like the MyFitness App, which allows you to manually fill out the date and time for any previous day. I like this because sometimes I forget to track workouts and this app (at least the free version) doesn’t allow you to add a workout to a previous day.

   wakeup2 · 31 Jul 2026

4. 5/5A year in , still the best, most personalized fitness app

   I’ve been using the Flex Premium app for a while now, and I especially want to talk about its AI training feature, which has honestly surprised me in a good way. At first, I asked the AI to generate a workout plan based on what had already been working for me and it did. What confused me at first was that it reduced the weights compared to what I had already been lifting. When I asked why, the AI explained that it wanted to focus on perfect form first, and then gradually increase the weights. This actually made sense and worked well. it gave my muscles a kind of “shock,” helped with recovery, and helped me regain strength more sustainably. One of the best things about the app is how it adapts every day based on what you did the day before. It automatically shifts the focus to different muscle groups so that, over time, your entire body is trained evenly. You don’t have to plan anything or worry about missing a muscle group, the AI remembers your progress, how much you can lift, when you struggled, and even shows which muscle groups have recovered. Another thing I really appreciated is how flexible it is with equipment availability. When I was working out at a gym that didn’t have all the machines I needed, I simply told the AI to generate a workout using only dumbbells, and it did. That was such a relief because it meant I could get a full workout anywhere, without needing a specific setup. Overall, I really believe that this kind of AI tool is incredibly useful, especially if you’re busy, don’t have time for a personal trainer, or want to save money. The form correction guidance is one of the most valuable features I’ve noticed in this version, and it really makes the workouts safer and more effective. I highly recommend it.

   Gissrv · 31 Jul 2026

5. 2/5Terrible Updates

   I want to be able to rate this app higher because I really love[d] a lot of the features and functionality; however I’m considering finding a new app to use before my premium subscription renews in a week. I have constant problems with this app due to updates that I assume are meant to fix bugs. There are many occasions when my phone and watch app do not sync, leading to inaccurate tracking, and one week ago my watch app disappeared completely. This is one of the features that I appreciate the most, and one of the reasons why I kept my premium subscription. I sought support in the app and never heard back, and now I don’t even have the option to request support (tapping the support tab in the app does nothing, shaking the phone to bring up the support message box does nothing). Last year, I was considering switching to a new app, but I decided to stick it out. Now, I do not think it’s worth it.

   Clynzee · 31 Jul 2026

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