Flex AI is the world’s first true AI personal trainer — built for lifters who want to train smarter, progress faster, and perfect their form.
Whether you’re chasing size, strength, or consistency, Flex uses real-time AI to guide every rep, adjust your program, and keep you motivated through challenges, leaderboards, and streaks.
- Your AI Coach, Every Rep
Personalized workouts built automatically by AI personas that learn your goals, history, and preferences.
Real-time form feedback powered by patented computer-vision AI — get instant corrections on squats, bench, deadlift, rows, and more.
Adaptive progression and deloading backed by sports-science principles — no spreadsheets, no guesswork.
- Train Smarter — See Results
AI tracks your strength curve and increases weight when you’re ready.
Visual progress graphs show PRs, volume, and recovery trends.
Track sets, reps, and tempo with a tap — or automatically with Apple Watch.
- Stay Motivated & Connected
Join a global community of lifters.
Compete on leaderboards, build streaks, and earn badges.
Post progress photos, celebrate milestones, and share results.
- Accessible to Everyone
Free to start with all core features included.
Upgrade anytime for advanced AI coaching and premium analytics.
Designed for all experience levels — from beginners to pros.
- Why Flex AI
Real-time AI form feedback (patented)
Adaptive, science-based programming
Progress tracking & recovery insights
Gamified streaks + leaderboards
Apple Watch integration
Built for hypertrophy & strength goals
Start Training Smarter — Today
Download Flex AI and experience personal training powered by real AI.
Perfect your form. Unlock your best lift. Train smarter — free on iPhone + Apple Watch.
Best Workout App for Intermediate and Advanced Training
XJRGU25
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.
Developer Response
Wow, thanks for taking the time sharing your detailed review with everyone! 12 years gymming is very impressive, that’s the sort of lifestyle we try to help promote 💪🏻
Great App
~(0_0~) ZombieGhost
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.
Developer Response
Thank you so much for your review! Please let us know if there's any way we can further improve the app for you by sending us a report/message in app.
Great Work Out app for Gym and At Home!
Karmma333
I have been through my fair share of work out apps, everyone of which limits what I can do and what types of work outs I can create for ME, so I wasn’t expecting much from Flex when I saw it advertised thinking it was like others but decided to try it out. I was pleasantly surprised when I saw I can create my own work out’s however many that it, my own work out plan. They let you completely customize and decide what you are going to be doing with your own work outs for free. They do provide work outs themselves and plans but you have to pay for some of them which is only expected. For someone who has a work out plan in their mind and just need the structure for said plan this app is perfect.
Barebones but with Style
Liam Bull
Was hospitalized last fall and lost 20 lbs where I was previously in fantastic shape, so was looking for anything to help make getting back into the gym as easy as possible as becoming more aware of the progress I lost felt demoralizing.This app caught my eye due to its gorgeous interface. Seriously, one of the sleekest designs I have ever used and combined with the smart progressive algorithm this has helped me make serious progress I didn’t consider possible.My criticisms: You are going to have to log an awkward amount of progress into the app before the smart progressive algorithm gets what you’re doing. It’ll drastically lowball the weight you can lift until you get tired of 95 for top sets and manually change it and then recommend weight much higher than you can do with good form.This in hand with your only other option for workout progressions as the “Inheritance” option in settings doesn’t give you great options other than to switch to an app such as Bolt (“inheritance” is admittedly a cool name for saying “there’s no algorithm, log it all manually”) or to put in weeks of work before the algorithm works itself out. Otherwise you’ve got a great option for a workout app and one I’ll probably stick with for a long time to come! Obviously if you want the best results find a trainer but I personally feel no shortage of features for the free version I use, the developers obviously care about their users and understand the difference between paid-for-features that make the experience better and the often seen progress-paywall features for apps of this kind.
Developer Response
Hey Liam - we just wanted to drop in a note to let you know we’ve read your review and are super proud of the progress you’ve made, congratulations! 🥳🪅 Also thanks so much for your detailed review! 🙏 We will certainly fine tune the algorithm moving forward!
• New design: Flex now has a revamped interface with a modern look and improved usability.
• Smarter AI trainer: Lex now creates and progresses your workouts with even more precision and intelligence.
• Performance improvements and bug fixes.
Version 3.1
The developer, Flex Artificial Intelligence Inc., indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Linked to You
The following data may be collected and linked to your identity:
Health & Fitness
Location
Contact Info
Identifiers
Usage Data
Diagnostics
Privacy practices may vary, for example, based on the features you use or your age. Learn More
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More