Introducing the Muscle Strength Score

Updated July 31, 2023

Screen of Fitbod's muscle strength score

For a while, Fitbod users have been asking for a way to measure strength and progress that doesn’t depend on repeating the same benchmark exercises—after all, a major reason why people love Fitbod is the variety of its recommendations. We heard you, and we’ve delivered. Get excited to see your strength and progress in a whole new way with our Muscle Strength score. 

We gave users like you previews of their Muscle Strength scores in our 2022 Year In Review. Now, Muscle Strength scores are available anytime in every user’s revamped Workout Report, available under Settings. These scores are dynamic. Fitbod will generate new Muscle Strength scores for you every week. You’ll get a ping to check out your updated scores as soon as they’re ready in your new Workout Report, but they’ll be available for you to check out whenever you’ve got time. Read on to learn more!

See how your strength changes over time

People love resistance training because it’s easy to gauge personal progress. Put on another plate, do another rep, hold a position longer: your numbers won’t lie and you’ll know where you stand. But that’s harder to nail down if your training varies from workout to workout.

That changes with Fitbod’s new Muscle Strength score. By compiling billions of data points and feeding them through our personal trainer-approved machine learning algorithm, we created this brand new metric for gauging progress. 

You’ll be able to track exactly how your strength changes over time for a specific muscle group, regardless of which specific exercises you do. That means you’ll know where your hard work is paying off—and where you might want to put in more focus.

You’ll also be able to figure out answers to these questions:

  • What are the relative strongest and weakest parts of my body?
  • I’m trying some new leg exercises—how are they impacting my quadricep and calf strength?
  • Am I making any progress toward my goal to increase my back strength?
  • And, settle it once and for all: Which of my friends has the strongest quads?
Sample Muscle Strength line graphs

Great. So how does it work?

Every Muscle Strength score is on a scale of 0-100+, where a score of 50 is what an average Fitbod user can lift (see FAQ below for more info). Lower is weaker, higher is stronger. The numbers are based on the relative strength of each muscle group—having a higher score in the biceps than the quadriceps does not mean your biceps can lift more weight than your quads.

With Muscle Strength now available in the Fitbod app, you’ll see how your workouts have affected each muscle group’s strength every week. Did you switch up your routine? Did you add new exercises? Are you training with a friend? Your Muscle Strength scores will show you how those changes have helped or hindered your strength progression.

How did Fitbod develop this metric?

Buckle up because we’re handing the keys over to our data science team! (Don’t have the stomach for stats? Jump to the FAQ for additional user tips.)

Graph showing normal distribution of muscle group strength scores

Imagine your Estimated Strength for the bench press is a one-rep max of 235 lbs and in pushups is a one-set max of 41 reps. What are your tricep and chest strengths?

This is exactly what we set out to answer with Muscle Strength scores.

Our first step was to use a static representation (i.e., a snapshot) of Fitbod population statistics to put every exercise effort on the same scale. Once we had all the exercises on the same scale, we had some questions to answer:

  1. How important are different types of strength in performing each exercise?
    • How do we quantify the importance of different strength types within an exercise?
    • Is chest or tricep strength more important in performing barbell bench press?
  2. Which exercises are the most and least indicative of each type of strength?
    • How do we quantify the importance of different exercises within strength types?
    • Are lat pulldowns or bicep curls more indicative of bicep strength?

We could have enlisted our personal trainers to manually estimate the contributions of each muscle group to each exercise, but that would have taken months and would be an approximation at best. So when you have billions of data points, why not use them to get an unbiased and data-based assessment of muscle group usage in each exercise? To do this, we created a novel machine-learning approach that aimed to answer the exact questions posed above.

The machine learning model followed the flow depicted below. For each exercise a user performed, the model took the importance-weighted average of all other normalized exercise strengths (excluding the chosen exercise) to generate muscle group strength scores. The model then took the importance-weighted average of those muscle group strength scores to predict the strength of that chosen exercise. The gap between the actual strength of the exercise and the predicted strength was then used to adjust the importance weights. The algorithm ran through our data until it had a sufficient understanding of the mapping between exercise and muscle group importance.

Flow chart to explain how Muscle Strength score machine learning model works

The result? We now know the importance of all of those arrows in the flow shown above. They show us just how important each muscle group is to each exercise in relative terms. 

For example, we found out that the Barbell Bench Press has relatively more to do with shoulder strength than chest strength. This doesn’t mean your shoulders are moving the weight more than your chest, but it does mean that your shoulder strength is more important in terms of predicting how much you can lift. We also are pretty sure that when you do Hip Thrusts, most of you out there are putting your heels too close to your butt, so you’re working your calves more than your glutes.

Most importantly though, we now can provide you with Muscle Strength scores that are reflective of just how strong you are in each muscle group according to all your lifts.

So, get out there! Go dive into your Muscle Strength scores every week in your Workout Report, available in Settings.


Q: Why am I compared to the average Fitbodder? Why not compare me to people who are the same gender, age, weight, etc?

A: We wanted to start everyone on the same line. That means the same level of strength on the same lifts will get you the same strength score and gaining 10 lbs in a particular lift will mean the same amount of progress, no matter who you are.

We plan to roll out rankings and percentiles of your strength score based on cross-sections of age, gender, height, and weight. That means that if you’re a 35-year-old, 5’4” woman who weighs 145 lbs, you could see that you are in the 80th percentile of users like you with your quadriceps strength score of 66.


Q: Is this score a percentile?

A: No, this score is not a percentile. While this score and percentiles are both calculated using population statistics, percentiles skew the data based on the curve of a normal distribution. The skew of percentiles causes the same 5 kg Estimated Strength gain to be a large jump for users near the average and to make almost no difference for users farther away from the average. Our score will increase by the same amount for any given 5 kg change in Estimated Strength.


Q: Will my scores change as the Fitbod population changes?

A: No. We have created a snapshot of the Fitbod population that will be fixed for the future, barring any unforeseen issues. So, if you do the same sets, reps, and weight of the same exercise for eternity, your associated scores will not change.


Q: Can my score go above 100?

A: Yes. There is always more progress to be made, so we didn’t want to limit the strength scores you can achieve. 1.67% of all weekly strength score data points are above 100 in our current historical data. If that’s you, know that you are in rarefied air.


Q: What if I cheat?

A: You won’t reap the benefits of this metric if you try to fake it. Plain and simple: You might see higher scores, but those numbers won’t translate to more strength. Your experience with the app will also likely suffer, as we plan on using these progress metrics to optimize your workout recommendations and fit your personal goals. If you enter fake values, your recommendations will get worse. In short, don’t do it.


Q: What is “mSTRENGTH”?

A: We needed to give Muscle Strength scores a unit to help you all understand that the number you’re seeing isn’t a percentile, nor is it pounds or kilograms. We chose “mSTRENGTH” to convey Muscle Strength—the Muscle Strength score and mSTRENGTH are exclusive to Fitbod.


Q: How can I see my Muscle Strength scores?

A: Muscle Strength scores are available in the new Workout Report,  accessible anytime in the Settings section of the app (i.e., go to the Log Tab and tap the gear icon in the upper right). We’ll also remind you to check out your updated Workout Report with a message in the Log Tab once a week. Simply tap into your Workout Report and scroll down to see your Muscle Strength scores.

Q: How often are Muscle Strength scores updated?

A: Muscle Strength scores are updated once a week. You should have fresh scores available every Sunday by 9 am UTC (i.e., early Sunday morning for our users in the western hemisphere and later on Sunday for those in the eastern hemisphere). We’ll remind you to check out your Muscle Strength scores in your Workout Report every week, both in the Log Tab and via email if you’ve opted in to receive Workout Reports. Check and update your email settings and communication preferences here.

Q: In my Workout Report, Why am I seeing Muscle Strength scores for some but not all muscle groups?

A: Muscle Strength scores are only generated for muscles that you have exercised several times. We also do not currently generate Muscle Strength scores for smaller muscle groups like forearms and neck due to the training data being too sparse to have confidence in our measurements, but we hope to add these muscle groups in the future.