How to Use the FITT Principle to Customize Your Workouts

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By adjusting four key elements of your workout, you can be your own personal trainer.
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With the wide variety of potential workouts and exercises, it can be challenging to put together a fitness routine on your own, especially if you want a sense of progress over a series of weeks. That's where the FITT Principle comes into play.

An acronym for "frequency, intensity, time and type," this structure is what many personal trainers use to build workouts for their clients, and what coaches rely on to help athletes level up in their chosen sports. Best of all, it's a highly adaptable framework that's suitable from everyone from exercise beginners to those returning from an injury to people training for specific events.

Let's take a look at each of the four elements, along with insights from experts on how to stack them together to create workouts that fit your goals.

Read more: How to Find a Workout You'll Actually Stick With

Frequency

This refers to how often you work out, usually determined by how many days or sessions per week you'll be taking on. If you have ambitious goals, it may be tempting to hit the gym every day, but keep in mind you should have some recovery days built in as well, says Life Time trainer Mark Issacson, CSCS.

"You don't want to exhaust yourself right away by coming to the gym too often, because that could cause early burnout," he says. "Be realistic in setting your frequency."

The Physical Activity Guidelines for Americans give a starting point. For strength training, they recommend at least two full-body sessions a week. But, Issacson points out, you can increase frequency later by splitting up your muscle groups — for example, doing leg day on Monday and upper body on Tuesday, so your lower body gets a rest day.

For cardio, the guidelines suggests moderate exercise five days a week, but if you're doing intense cardio — think sprinting, bootcamp classes, HIIT workouts and high-energy group training — start at just two to three days per week.

The Takeaway

The first part of the FITT principle is the frequency of your workouts, which is how often you exercise. When setting your frequency, be realistic and start with two strength sessions and two to three cardio sessions each week.

Intensity

How hard you work during exercise is the intensity element, and you'll likely see suggestions based on definitions like "moderate intensity" or "vigorous intensity."

You can measure this in a few ways. For cardio, that may include a heart rate monitor or the "talk test" — the higher your intensity level, the more challenging it will be to talk in more than a few words before getting out of breath.

For strength training, intensity is generally measured less by your physiological responses and more in terms of reps, sets and amount of resistance. For example, you can increase intensity by lifting more weight or doing more reps.

When increasing your intensity, either in cardio or strength training, it's helpful to think about your rate of perceived exertion, also called RPE. This is a subjective measure, but it's useful for increasing intensity over time, says Ariel Osharenko, CSCS, a sports performance physical therapist and trainer.

For example, working at around a 7 out of 10 on the RPE scale can keep you from increasing your intensity too quickly, Osharenko says. "If you are all out, 10 out of 10, you're going to fatigue quickly," he says. "That's usually the point where you may be at higher injury risk as well because your form will start to suffer." So turn up the intensity gradually.

The Takeaway

The second part of FITT is your intensity, which is how hard you're exercising. Use a rate of perceived exertion (RPE) to rank your workout on a scale of 1 (super easy) to 10 (completely exhausting). In general, you'll want to stick to around a 7 on the scale.

Read more: What Is Your MHR — and How Do You Calculate It?

Time

Once you've set frequency and intensity, you can decide on how long your each sweat session will be. Issacson says 30 minutes tends to be a good starting point. From there, you can work up to an hour, depending on what type of exercise you're doing.

For example, if you're doing intervals (ex. sprinting or jumping rope), just a few minutes per set is likely enough, with four to five sets. That might give you a Tabata-style workout (20 seconds working, 10 seconds resting, repeated eight times) that's less than 15 minutes.

If you're doing strength training, the length of your session will depend on whether you're lifting heavy and doing fewer reps and fewer sets or going lighter with more reps and more sets. The latter, obviously, will take more time.

"Switching up your time, along with your intensity, can be very beneficial," Issacson says. "For example, if you went hard yesterday for an hour, maybe you do light conditioning today, with an easy elliptical session for 20 minutes. That can help balance you out."

The Takeaway

The first T in the FITT Principle refers to the amount of time you spend working out. Start with 30 minutes and gradually progress to hour-long sessions. As you grow more experienced, vary the amount of time you spend exercising.

Type

Of all the variables, this one might be the most fun to change up, because there are so many options, Issacson says. "Type" is the kind of exercise you do, and it runs the gamut from cycling, swimming, dancing and Zumba to plyometrics, body-weight strength sessions and kettlebell workouts.

To have a sense of progress, it's beneficial to stay with one type of exercise — for example, if you're training for your first 5K, you'll want to focus on running — but adding in different types for cross-training can keep you from getting bored and also help prevent overuse injuries, Issacson says.

You can also change your type within the same general exercise category. For instance, with strength training, you can vary your workout by using different types of equipment, including dumbbells, barbells, kettlebells, resistance bands and medicine balls.

The Takeaway

The last part of the principle is the type of exercise you're doing. This is the fun part, as there's a nearly endless variety of forms of exercise you can try, like cycling, swimming or dancing. You can also vary your type of exercise by trying new equipment.

Read more: Can Muscle Confusion Be the Key to Overcoming a Weight-Loss Plateau?

How to Use the FITT Principle

Playing around with different combinations of the four FITT Principle elements gives you a wide array of workouts. So how do you make sure you're snapping those pieces into place properly?

It's helpful to set a goal first, says Ali Greenman, CPT, founder of Final Straw Fitness, then work your way backward in your FITT plan to your starting point. For example, let's say you want to strengthen your lower body, especially your legs. Using FITT, this is how Greenman would set up your first week:

Sample Workout Routine Using the FITT Principle

  • Frequency: Because you’re determined to build strong legs, concentrate on them two to three times a week. That means you could do: Monday, Wednesday and Friday as “leg days” with different muscles of the legs — quads, glutes and hamstrings — as your main focus those days. If you want to go to the gym six days a week, the other three days would be for chest, back and core to give your leg muscles ample recovery time.
  • Intensity: Like other trainers, Greenman suggests an RPE of 7 out of 10. She also advises clients to begin with a plan in mind and eliminate distractions — no texting between sets or chatting with gym buddies during your reps. “Keep your intensity on track by getting in there, and getting it done,” she says.
  • Time: With this type of strength training, the focus will be on slow, intentional reps with a full range of motion. “I would even play with the tempo,” Greenman says. Try lowering down into a squat for five seconds, pausing for three seconds, then coming up in one second. That can help you increase the difficulty without having to do a ton or reps or lift a lot of weight.
  • Type: Varying your exercises by using compound movements (exercises that involve more than one joint) will help prevent overuse injuries, she says. For example, a squat with movement at the hip, knee and ankle is better than a leg extension, which only gives you movement at the knee. Another example is a deadlift, which builds the glutes and hamstrings.

Using FITT for cardio can follow the same framework and many of the same suggestions — build in rest days, stay at a 7 RPE, play around with the time you spend on each exercise and be sure to cross-train to vary your workout type.

"Using the FITT principle gives you a good way to modify your workout in numerous ways," Issacson says. "Sometimes, just playing with one variable within that plan can make a big difference."

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