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.
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 and high-energy group training — start at just two to three days per week.
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 find this measure in a few ways, including monitoring your heart rate and doing a "talk test" during cardio exercise, which means the higher your intensity level, the more challenging it will be to talk in more than a few words before getting out of breath.
Intensity in strength training is measured less in physiological responses and more in terms of your reps, sets and amount of resistance. For example, you can increase intensity by lifting more weight or doing more sets.
When increasing your intensity, either in cardio or strength training, it's helpful to think about your perceived rate of exertion, also called PRE. 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 PRE scale can keep you from increasing your intensity too quickly, he suggests.
"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. Take your intensity up gradually."
Read more: 4 Signs You're Ready to Lift Heavier Weights
Once you've set frequency and intensity, you can decide on how long your actual workout session will be. Issacson suggests that 30 minutes tends to be a good stretch for getting started, then working up to an hour, based on what type of exercise you're doing.
For example, if you're doing intervals like 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 that's less than 15 minutes.
If you're 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," says Issacson. "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."
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, from resistance bands to medicine balls.
Read more: What Activities Actually Count as Cardio?
Putting a FITT Plan Together
Playing around with different combinations of the four FITT Principle elements gives you an almost endless 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:
- Frequency: Because you're determined to build strong legs, you'll want to concentrate on them two to three times a week. That means you could do: Monday, Wednesday and Friday as "leg days" with different areas 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.
- Intensity: Like other trainers, Greenman suggests a PRE of 7 out of 10. She also advises clients to begin with a plan in mind and put in the work — no texting between sets or chatting with gym buddies as you're doing 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," says Greenman. Try lowering in a squat for five seconds, pausing for three seconds, and coming up in one second. That can help you increase tension without having to do a ton or reps or lift a lot of weight.
- Type: Varying your exercises by using compound movements will help prevent overuse injuries, she says, especially if you use more than one joint. 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 strong 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, increase intensity by staying at a 7 PRE, 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."