Max Effort Day: how to do it like a pro, according to data from 148 million exercise sets

Head of Data Science at Fitbod

Understanding Max Effort Training for Optimal Strength Gains

Fitbod takes the guesswork out of your training. Every time you open the app, you get a personalized workout that tells you exactly what to do: which exercises to perform, how many sets and reps to complete, and how much weight to use. We even tell you how long to rest between sets and we show you videos demonstrating proper form. Just hit the gym (or your garage, or living room) and start working out – we’ve got your back.

But sometimes, we like to give you more freedom. If you’ve been using Fitbod for a while, you may have noticed that occasionally your exercise recommendation looks a bit different. We call these special recommendations “max effort days.” They look like this:

What makes these recommendations special? Look for the plus (+) sign next to the rep numbers in your final two sets. That little symbol means we want you to do at least that many reps, but ideally more. How many more? As many as you safely can! That’s why we call them max effort days.

Why Do We Have Max Effort Days?

Two reasons:

1. They help us better calibrate your future workouts by understanding your true strength level.
2. They push you beyond your comfort zone, which is key for getting stronger.

💡 Quick Tip: The first two sets of any max effort day are just normal sets. Just do the recommended reps for these – save your energy for the final push!

In the end it’s about progressive overload: helping you increase your 1RM over time.

The Science Behind Progressive Overload and Max Effort

Does pushing yourself on max effort days really make you stronger? Our data says yes – and we have a lot of data! We looked into 148 million sets to find this answer. Every rep, every weight, every rest interval – it’s all there in our database, telling us what works and what doesn’t.

How We Measured Effort In This Analysis

We compared your Estimated Strength from sets 1-2 (regular sets) to your Estimated Strength from sets 3-4 (max effort sets). The latter divided by the former is what we’re calling effort for the purposes of this analysis.

In case you haven’t encountered it before, Estimated Strength is a metric that lets us compare performances even when the number of reps and/or the weights are different. We explain all about Estimated Strength in a previous blog post.

Another way to interpret Estimated Strength is: it’s the weight we think you could lift in one series of one repetition of a given exercise. That’s why it’s also called One-Rep-Max (1RM).

Let’s use a simple example: say you do 10 reps with 20 lbs in your regular sets, then 15 reps with 25 lbs in your max effort sets. Using our mathematical model, we can calculate that this is equivalent to having 1RM of 27.6 lbs and of 42.4 lbs respectively. If we divide the latter by the former we find an effort of 53.6%. Meaning: you pushed yourself 53.6% harder in your max effort sets than in your regular sets.

What the Workout Data Shows About Strength Progression

Our analysis reveals a clear pattern: the harder you push yourself on max effort days, the stronger you get. Using our data, we created a mathematical model of how effort and gains are related. This is the result:

So:

• If you push 20% harder, you typically see a 15% strength gain.
• Push 40% harder? You’re looking at a 23% strength gain.
• And the pattern continues – more effort equals more progress.

To be clear, the relationship between effort and gain is not always those neat lines you see in the graphs above. In reality, that relationship depends on multiple factors. For instance, it depends on your starting point (were you already pretty strong when you did your first max effort day?) and on which exercise we are talking about. The graph above is an average across all users (and in the first graph, across all exercises), and averages can mask a lot of variation. But these overall averages show us that, typically, we should expect more effort to result in more gains.

Another way to go about this is to compare low-effort and high-effort users over time. For instance, if we take the 25% lifters with lowest effort, and the 25% lifters with highest effort, this is how their Back Squat 1RMs vary between their first and fifth max effort days: 

So, users who consistently gave their all on max effort days saw their strength increase by 25% over their first five sessions. Those who took it easier? Only about 7% improvement. That’s more than a 3x difference!

Common Questions and Tips

“So if I do 20% more reps on the max effort sets I get a 15% gain?”

Not quite. The numbers above are based on a comparison of One-Rep-Maxes (1RMs), not on a comparison of reps. We can’t compare reps directly since you can manually change the weights. And doing 20% more reps doesn’t mean you’re doing a 20% higher 1RM.

For instance, doing 2 sets of 10 reps with 20 lbs means a 1RM of 27.6 lbs. If you increase the number of reps by 20% then you’re doing 2 sets of 12 reps with 20 lbs. And that’s a 1RM of… 29.8 lbs. That’s only a 7.9% increase in 1RM, not a 20% increase.

“Well then, what exactly am I supposed to do on max effort days?” Go all in. Do as many reps as you can. Go until you can’t safely continue anymore. That’s it. Don’t make it about math. Just do as much as you can in those two final sets.

“What if it takes too many reps to reach my limit?”

If you’re finding yourself doing endless reps before feeling challenged, there’s a simple solution: increase the weight!

Looking at the data, we found that for some exercises, on max effort days, users barely increase the number of reps, and put all the effort into increasing the weights. Examples:

• Barbell Bench Press
• Deadlift
• Back Squat
• Olympic lifts

“What about exercises where I can’t add more weight?”

Some exercises, by their nature, are all about rep count. Take the Partner Sit-Up Toss – you’re not going to throw a 100-lb medicine ball at your workout buddy! For these types of exercises, pushing for more reps is really your path to progress:

• Medicine ball exercises
• Band workouts
• Bodyweight movements
• Kettlebell exercises
• Plate flips

Know When to Stop

Here’s a crucial distinction many people miss: there’s a difference between discomfort and failure. Many stop at the first sign of discomfort, thinking they’ve reached their limit. But research shows people often underestimate their true failure point by 5 reps or more!

⚠️ Important Safety Note: While we want you to push yourself, safety comes first. With heavy exercises like Barbell Bench Press, stop a few reps short of failure if you don’t have a spotter. You can go closer to true failure with safer exercises like Push Up.

Ready to Max Out?

If you’re not using Fitbod yet, get it now! You should see your first Max Effort Days after a couple of workouts.

Need some extra motivation for your next max effort day? Research suggests cranking up some high-tempo music can help you push harder. Whatever gets you fired up – use it!

Remember: whether you’re adding weight or cranking out more reps, the key is to challenge yourself. That’s how you get stronger. Now get out there and crush your next max effort day!

About the Author

Thiago Marzagão is Head of Data Science at Fitbod, where he combines data science with exercise science to help create smarter, more effective, and more personalized workouts. He has a Ph.D. from the Ohio State University and peer-reviewed publications in top econometrics journals. He is a former professor of statistics and machine learning and lectured at public and private universities. Reach out to Thiago at [email protected]