The Science Behind Fitbod’s Recommendations

How Fitbod Calculates One-Rep Max, Reps and Sets

August 22, 2019

By Mary Brandeau

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Fitbod’s exercise recommendations are formulated specifically for you, to help you accomplish your fitness goals safely, methodically, and without guesswork. As you progress through your exercise plan and see improvements, you might wonder about the science behind Fitbod’s recommendations. Let’s take a look at what goes into your customized exercise suggestions and how Fitbod fine-tunes these over time.

Fitbod’s exercise recommendations are based on how much weight you can lift and how often and in what order you should lift the weights. This means that Fitbod needs to know details about you and your physical capabilities right from the start. 

At first, Fitbod knows only the basics – your age, gender, height and weight, skill level, fitness goals, available equipment, target workout duration – with which it develops your workout plan. Drawing from its vast database of user experience and data points, Fitbod estimates how much weight you can lift at one time, also called the One-Repetition Maximum or 1RM, and recommends the reps and sets for various exercises. A 135 lb woman normally will have a lower 1RM than a 190 lb man (unless she’s an experienced weightlifter!)

The 1RM is the theoretical maximum weight you can lift at one time for a specific exercise. Of course, unless you test this yourself, which is not recommended for safety reasons, your 1RM needs to be determined by an indirect method.

Brzycki Formula

There are several widely known ways of calculating your 1RM, among them the popular Brzycki formula. Matthew Brzycki developed this formula while working with athletes at Princeton University in the 1990’s in his role as coach and coordinator of Health Fitness, Strength and Conditioning Programs. The formula looks like this:

 
W = the weight lifted in repetitions  R = the number of reps lifting the weight

W = the weight lifted in repetitions

R = the number of reps lifting the weight

 

Fitbod uses a modified Brzycki formula to calculate the 1RM for your exercise plan so that you are not at your maximum effort every single time you lift. Your weight recommendations are meant to help you avoid injury and provide latitude for you to increase or decrease weight as desired. As you log your exercises, Fitbod adjusts your 1RM to more closely reflect your actual weightlifting ability so that you progress but do not over-tax yourself.

Prilepin Formula

With your 1RM estimated, Fitbod uses a modified Prilepin formula to determine the recommended sets and reps for a workout. A.S. Prilepin, a Soviet weightlifting coach of the 1970’s-1980’s, developed this chart through analyzing the workouts of Soviet National Team Olympic weightlifters. It outlines the optimal amount of reps and reps per set that a lifter should follow to gain the most from a workout without losing power; not too much but not too little. 

The chart looks like this:

 
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We can interpret this information with an example. If your 1RM is 40 lbs and you are lifting 75% of your 1RM (30 lbs), you should perform 3 to 6 reps per set and preferably about 18 reps in the total range of 12 to 24 reps.

One of the limitations of strictly following the chart is that its data focused on Olympic weightlifters who performed only the Snatch and Clean and Jerk and were concerned mostly with quickness and not necessarily strength or muscle building. What about those who have other fitness goals, such as bodybuilding or toning muscle and losing weight? Not everyone wants a program for Olympic weightlifting! Don’t worry, Fitbod’s algorithm modifies these guidelines when recommending your exercises so that they suit your specified fitness goals.

Barbell Bench Press Example for an Intermediate Powerlifting Female

How does this all fit together in the app? An example might help you understand all the pieces.

For example, to start, the app can recommend a female with fitness experience set to Intermediate and goal set to Powerlifting with initial 1RM of 73 lbs, the barbell bench press, at 5 sets of 5 reps at 65 lbs. Assuming she completes this rep scheme as recommended, the app can later generate a recommendation such as 5 sets of 10 reps at 50 lbs.

If she completes this successfully, the next time this exercise is programmed, the recommendation might be 5 sets of 4 reps at 70 lbs.

Following these rep schemes can change her projected 1RM to slightly over 85 lbs from initial 1RM of 73 lbs (note that this does not take into account any Max Effort Day for this exercise, which can also affect her projected 1RM).

In another article, we will review how Fitbod varies your suggested exercises and uses the Max Effort Day feature to mix up the intensity and volume of your workouts and help you maximize their effectiveness as you work toward your fitness goals.

 
Jesse Venticinque