The FITT Principle: Design a Workout That Gets Results

How Do You Design a Workout Plan Using the FITT Principle?

Update 4/2026

Personal trainers use a framework called the FITT Principle to design exercise programs for their clients. Now it’s time for you to take charge of your workout plan. If you have already set a specific fitness goal and have a sense of your current fitness level, you can use this formula to design a workout plan that leads to results.

What Is the FITT Principle?

FITT stands for frequency, intensity, time, and type. These four variables work together in an effective plan. If you’re pregnant, I like to add a third T, which stands for Trimester. I go into this in my book, Active Mom.

Frequency is how often you exercise. Intensity is how hard you work. Time is how long each session lasts. Type is the kind of exercise you're doing, such as running, cycling, strength training, or swimming.

The first thing to understand is that these variables are interdependent. The intensity will affect how long each session is, and the type may impact frequency. Without having a degree in exercise science, understanding that one change can impact another variable is the first step in creating and sustaining your fitness plan. Because frequency, intensity, time, and type are connected, changing one means you should consider whether you need to manipulate the others. If you increase the intensity of your workouts and don’t adapt frequency to allow for recovery, you may not get the results you’re hoping for.

How to Use FITT to Build Your Plan

Let's look at a practical example. A healthy mom of two who can barely find time to workout, but enjoys exercising outside, wants to meet general health guidelines. Because the number of days she can find time to work out is her limiting factor, she decides to start with the frequency variable. She can realistically commit to 2-3 days per week. On one of the days, her kids stay later at school, so she decides she can fit in one 45-minute workout on that day, but the other 1-2 days will have to be 30 minutes. Now she has frequency and time determined. She’s a fairly experienced exerciser with no injuries or limitations, so when she chooses intensity, she decides that for the shorter workouts, she will exercise at higher intensities and on the longer day, she’ll do something more moderate like brisk walking or a bike ride.

This is how to manipulate variables to meet your goals and make your workout fit your lifestyle. For some of you, your starting factor might be intensity. If you’re avoiding high-intensity exercise, your type and frequency should correspond.

As a disclaimer, it’s not always that simple, and plenty of other barriers or considerations may exist for you, especially during and after pregnancy, but as I said, it’s a foundational starting point and worth considering.

Let’s take a look at the guidelines so that you understand what is recommended, and you can use the FITT(T, for Trimester) principle to personalize your plan. As a side note, if you need more guidance than this article, the Active Mom book is a comprehensive guide to help you personalize exercise and understand your needs so you can stay active through all stages of motherhood.

ACSM Aerobic Exercise Guidelines

The following are general aerobic exercise guidelines for most adults based on current ACSM recommendations. Use these as a starting point, not a prescription. Your specific goal, fitness level, stage of motherhood, and schedule will determine where within these ranges makes sense for you.

• Frequency: 3 to 5 days per week

• Intensity: Moderate to vigorous. Moderate intensity means you can talk but not sing during the activity. Vigorous intensity means you can only say a few words before needing to catch your breath.

• Time: 150 to 300 minutes of moderate intensity activity per week, or 75 to 150 minutes of vigorous intensity activity per week. These can be accumulated in single sessions or broken into shorter segments of at least 10 minutes.

• Type: Any sustained, rhythmic activity that elevates your heart rate. Walking, cycling, swimming, dancing, running, and rowing all qualify. Choose something you will actually do consistently.

Don't Forget Resistance Training

Aerobic exercise is only part of the picture. A complete plan includes resistance training, and the FITT principle applies here, too. Current ACSM guidelines, updated in 2026, recommend training all major muscle groups at least twice a week. Consistency and effort matter more than complexity. Whether you are using barbells, resistance bands, or bodyweight, choose an approach that fits your life and build from there.