Comparison

Flex AI Workout Trainer & Log vs Muscle Booster Workout Tracker

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

Flex AI Workout Trainer & Log

This app uses AI to provide personalized workout plans and real-time form feedback for weightlifters. It tracks progress, offers adaptive progression, and includes motivational features like leaderboards and streaks. It's designed for all experience levels, from beginners to pros.

Highlights
  • AI personal trainer
  • Real-time form feedback
  • Personalized workout plans
  • Adaptive progression
  • Strength tracking
  • Community leaderboards
  • Apple Watch integration
Features
Read full description

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.

About

Muscle Booster Workout Tracker

This app acts as a personal trainer, creating customized workout plans for muscle gain, weight loss, or recovery. It offers a vast library of exercises and challenges for home or gym, adapting to your available equipment and goals.

Highlights
  • Personalized workout plans
  • 1000+ exercise library
  • Home and gym workouts
  • Calisthenics and weight loss plans
  • Workout timer and audio tips
  • Equipment-based plan creation
  • Muscle recovery guidance
Features
Read full description

Take your fitness journey to the next level with Muscle Booster Workout Tracker, the ultimate Workout Planner that integrates with your Apple Watch. Train anywhere, anytime with a complete gym & exercise app designed to help you get fit. What are you waiting for? MUSCLE BOOSTER WILL HELP YOU TO: Build muscle, sync with Apple Health, and boost your fitness schedule from home! With an integrated calorie tracker, body editor plan, and step-by-step gym workouts, you can stay motivated, get your belly flat, monitor your health, and achieve your fitness goals anywhere. Anywhere, Anytime! Whether you prefer home workouts, calisthenics, core, or weight loss, Muscle Booster provides personalized training plans for all levels. Work with your own digital coach and follow structured gym routines inspired by popular fitness and gym pros. Track your strength gains, body measurements, and fat loss with smart analytics and stay consistent in building a strong exercise routine and a healthy body. Explore hundreds of exercises and plans. Workout tracker, AI calorie tracker, and weight loss Strength training, HIIT, core, weightlifting, bodyweight calisthenics. Abs and belly training. Enjoy personalized sessions tailored to your fitness level. Build muscle, burn fat, and maintain overall health. Use the workout planner to schedule sessions and combine gym routines. Track your performance and measure your progress over time on Apple Health. Personalize your home workouts Workouts, calories burned, and heart rate in real-time. Customize your home workout sessions or gym routines with guided workouts, a training planner, anytime fitness, and exercises targeting your core, arms, legs, and full body. Whether your goal is to lift, get fit, or simply stay active, Muscle Booster keeps your activity high with interactive videos, progress tracking, and social features to connect with friends and fitness hotschedules. Customize your exercise routines on the go Join the community of weightlifting enthusiasts and get inspired by training programs from pros, and more. Train at home, in the gym, or on the go, with the flexibility to adapt exercise routines anytime. Track your progress with smart analytics, manage your diet, and see real-time results with Apple Watch integration. Whether you are following a body coach plan, a workout app program, or creating your own custom gym routines, Muscle Booster makes it easy to stay consistent and achieve your objectives. Designed for all fitness stages Muscle Booster Home Workout combines the best of home workouts, sports training, calisthenics, strength training, and guided video exercises into a single exercise app. With personalized workout plans, motivational tools, and a comprehensive tracker, you can lose fat, get stronger, and transform your body efficiently. Perfect for all levels, from beginners to advanced athletes, the app ensures your training is smart, effective, and fun. Follow your progress, stay inspired Take control of your health and training today. Use Muscle Booster for gym workout, home workouts, core, running, and all your sports needs. Track your progress, stay motivated, and become the strongest, healthiest version of yourself. With a full workout planner, personal coach features, and integration with your device, your goals are within reach. SUBSCRIPTION INFO: Download the app at no initial cost. Further use requires a subscription. A trial may be offered as indicated in the app. Subscription prices are shown in the app and charged to your Apple ID upon purchase confirmation. Subscriptions renew automatically unless auto-renewal is turned off at least 24 hours before the current period ends. Renewal charges occur within 24 hours before the current period expires. Terms of Use: https://legal.muscle-booster.io/page/terms-of-use Privacy Notice: https://legal.muscle-booster.io/page/privacy-policy

Screenshots

Flex AI Workout Trainer & Log4 screens
Muscle Booster Workout Tracker4 screens

Verdict

The call

Flex AI Workout Trainer & Log and Muscle Booster Workout Tracker both sit at 4.6 stars, but that hides the real split: 69% of Flex AI Workout Trainer & Log's written reviews are positive against 43% of Muscle Booster Workout Tracker's. Muscle Booster Workout Tracker's advantage is ratings volume (138K vs 2.4K) and chart position (#62 vs unranked). On price, rating, update cadence and ads there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. Flex AI Workout Trainer & Log sells 8 in-app purchases, starting at $1.99 per month and Muscle Booster Workout Tracker sells 16 in-app purchases, starting at $9.99 per 7 days. Whichever you choose, the download price is not the number that matters.

ReceptionRating · Positive reviews · Number of ratings

On the App Store both sit at effectively the same score — 4.6 for Flex AI Workout Trainer & Log against 4.5 for Muscle Booster Workout Tracker. That said, the two scores are not equally well evidenced: Muscle Booster Workout Tracker has 138K ratings behind it against 2.4K, so its average is the more settled of the two. Written reviews are what separate them: 69% of Flex AI Workout Trainer & Log's written reviews are positive against 43% of Muscle Booster Workout Tracker's.

UpkeepUpdate frequency

Flex AI Workout Trainer & Log ships an update every 9 days, Muscle Booster Workout Tracker every 2 weeks. The most recent releases landed on September 23, 2026 and September 24, 2026 respectively.

Scorecard3 real differences · 8 level
Flex AI Workout Trainer & Log versus Muscle Booster Workout Tracker: the parameters behind the verdict, then further details
ParameterFlex AI Workout Trainer & LogMuscle Booster Workout Tracker
PriceFreeFree
Rating4.6 (2.4K ratings) — better4.5 (138K ratings)
Positive reviews69.3% of reviews — better43.5% of reviews
Number of ratings2.4K138K — better
Update frequencyEvery 9 days — betterEvery 2 weeks
AdsNoNo
In-app purchasesYesYes
MonetizationFreemiumFree with in-app purchases
Best chart rank#62 — better
DevicesiPhone, Apple WatchiPhone, Apple Watch
Requires iOS18.017.0 — better
Further details — not scored
Size574 MB574 MB
Age rating17+17+
DeveloperFlex Artificial Intelligence Inc.WELLTECH APPS LIMITED

Customer experience

Flex AI Workout Trainer & Log

All ratings2,405 ratings
Positive92.0%
Neutral2.6%
Negative5.4%
Written reviews303 reviews
Positive69.3%
Neutral6.6%
Negative24.1%

Muscle Booster Workout Tracker

All ratings137,667 ratings
Positive89.5%
Neutral3.6%
Negative7.0%
Written reviews2,842 reviews
Positive43.5%
Neutral8.1%
Negative48.4%

User reviews

Flex AI Workout Trainer & Log

From 2.4K App Store ratings

What we love

  • 🚀 Detailed workout tracking
  • 👍 Customizable workouts
  • 🔒 Comprehensive exercise library
  • 💡 Helpful progress tracking
  • 👍 Clean and intuitive interface

Room to improve

  • 🐛 Glitches and bugs
  • 💰 Expensive premium subscription
  • 🔒 Limited functionality without premium
  • 🐛 Inconsistent rest timer
  • 🐛 Workout data loss

Muscle Booster Workout Tracker

From 138K App Store ratings

What we love

  • 🚀 Great workouts
  • 👍 Easy to follow
  • 👍 Variety of exercises
  • 🚀 Customizable plans
  • 👍 Helpful for beginners

Room to improve

  • 🐛 Buggy app performance
  • 🔒 Lack of free trial
  • 💰 Expensive subscription
  • 👎 Limited gym equipment options
  • 👎 Repetitive exercises

Bugs and requests

Flex AI Workout Trainer & Log

Reported bugs

3 issues
  • App crashes on iOS 16 update
  • Inability to log workouts on previous days
  • Inconsistent syncing between app and Apple Watch

Requested features

4 requests
  • Offline workout mode
  • Ability to save and reuse custom workout plans
  • Muscle group targeting and analytics
  • Social features and community integration

Muscle Booster Workout Tracker

Reported bugs

5 issues
  • Workouts not logging properly
  • App freezing and crashing
  • Sync issues with Apple Watch
  • Inaccurate exercise counting
  • Inability to contact customer support

Requested features

5 requests
  • Ability to track progress and weights
  • Better integration with Apple Health
  • More personalized meal plans
  • Ability to customize workout schedules
  • Audio/voice guidance during workouts

In-app purchases

8 purchases

Flex AI Workout Trainer & Log

Subscriptions6
  • Premium Subscription Monthly$1.991 Month
  • Premium Plus Monthly$2.991 Month
  • Premium Yearly Subscription$9.991 Year
Show 3 more
  • Premium Plus Family Monthly$9.991 Month
  • Premium Plus Yearly7 Days trial$19.991 Year
  • Premium Plus Family Yearly7 Days trial$49.991 Year
One-time2
  • 1 Month Free PremiumFree
  • Lifetime Free PremiumFree
16 purchases

Muscle Booster Workout Tracker

Subscriptions15
  • 1 Week Subscription7 Days trial$9.997 Days
  • 1 Week Subscription$9.997 Days
  • 1 Week Subscription7 Days trial$14.997 Days
Show 12 more
  • 1 Month Premium$14.991 Month
  • Muscle Booster$14.991 Month
  • Muscle Booster Workout Premium3 variants$19.991 Month
  • 1 Month Subscription$19.991 Month
  • 1 Month 22.99 with 7-day free trial7 Days trial$22.991 Month
  • 1 Month Subscription$24.991 Month
  • 3 Month Subscription3 variants$29.993 Months
  • 3 Month Premium6 Months trial$39.993 Months
  • 3 Months Subscription6 Months trial$39.993 Months
  • 1 Year Premium2 variants$59.991 Year
  • Muscle Booster Premium$59.991 Year
  • 12 Month Subscription$79.991 Year
One-time1
  • Premium Bundle$29.99

Questions

Is Flex AI Workout Trainer & Log free?
Flex AI Workout Trainer & Log is free to download, with in-app purchases available.
Is Muscle Booster Workout Tracker free?
Muscle Booster Workout Tracker is free to download, with in-app purchases available.
Which has better reviews, Flex AI Workout Trainer & Log or Muscle Booster Workout Tracker?
Flex AI Workout Trainer & Log is rated higher. Flex AI Workout Trainer & Log averages 4.6 out of 5 from 2.4K ratings, while Muscle Booster Workout Tracker averages 4.5 from 138K ratings.
Do Flex AI Workout Trainer & Log or Muscle Booster Workout Tracker have ads?
Neither Flex AI Workout Trainer & Log nor Muscle Booster Workout Tracker shows ads.
Which is updated more often, Flex AI Workout Trainer & Log or Muscle Booster Workout Tracker?
Flex AI Workout Trainer & Log ships an update every 9 days, and Muscle Booster Workout Tracker every 2 weeks. Most recently, Flex AI Workout Trainer & Log was updated on September 23, 2026 and Muscle Booster Workout Tracker on September 24, 2026.

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