top of page

FITT Principle | How To Apply FITT To Training

A woman performing body weight exercises. The image heads the article that explains the fitt principle.

FITT is an acronym for frequency, intensity, time, type and the fitt principle is a framework that can be used to guide the construction of an exercise programme.

The components of fitt ‘help ensure that principles are adhered to, but more specifically ensure that training takes place often, is increasingly harder over time, is increasingly longer over time, and trains the correct areas of fitness,’ (Royal Marines Fitness | Physical Training Manual).

The aim of this article, then, is to outline each component of the fitt principle. In addition, we will review how the fitt principle can be applied to an exercise programme.

But, before we take a look at the fitt principle proper, I have outlined a number of benefits and answered a few FAQs concerning this underused training principle.

Why fitt principle is important

If applied correctly the fitt principle can enable you to develop an effective training programme that delivers desired results. For example, the outcome of improved fitness or changes in body composition is influenced by the variables that comprise the fitt principle.

Physiological adaptations, such as increased strength or improved aerobic performance, will not occur unless we train these components of fitness frequently.

Furthermore, the rate of development can be manipulated by the intensity at which we exercise and how long – the time – we spend engaging in exercise.

But, even if we train frequently, at varying intensities and for sustained periods, if we engage in suboptimal exercises all our efforts will account for little and could lead us away from our fitness goals.

Thus, understanding and applying the fitt principle can greatly improve fitness outcomes.

What are the four parts of the f.i.t.t. principle?

F = Frequency

I = Intensity

T = Time

T = Type

Benefits of the fitt principle

As stated above, the primary purpose of the fitt principle is to support the development of a training programme. But the fitt principle can also be used to assess a general exercise routine.

A beginner trainer could use fitt to assess their routine. By applying the fitt principle they could gain insight into whether they are exercising frequently enough, or if the intensity and time of each session are sufficient.

In extension, someone pursuing a specific fitness goal could use fitt if they felt they were not making adequate progress. Say they were preparing for a 5-kilometre running event and failed to make a milestone, applying the fitt principle may enable them to identify limitations of their training process.

Even advanced trainers and athletes can benefit from the fitt principle. If expected fitness advancements were not forthcoming or a performance target wasn’t met, these are indications that their training programme may need amending. Again, the fitt principle could be used here to perform a diagnostic on the programme.

FITT Principle #Frequency

Frequency refers to the number of training sessions a person participates in over a given period. At its essence, frequency is about how often you workout each week.

Exercise frequency is arguably the most important component of the fitt principle. Without maintaining a level of exercise consistency, the intensity, duration, and type of training we engage in will count for little. One super-long, high-intense weekly workout will not yield the same fitness results as three or four short, light- to moderate-intensity workouts.

‘In general, training for only 1 day per week does not yield improvements,’ (Physical Fitness & Athletic Performance).

Optimum training frequency

So, if you can’t get away with one super sweat session, what is the optimal number of weekly workouts?

Exercise frequency is influenced most by your fitness goals. For example, if you aspire to maintain a general level of fitness while exploiting the health benefits associated with exercise, the NHS recommends three to four 30-minute light- to moderate-intensity workouts each week.

According to Watson (1999), author of Physical Fitness & Athletic Performance, fitness gains have been reported with training programmes as short as 2 days. However, he goes on to say that 3 days is recommended.

Achieve your fitness goal with the fitt principle

But if your training goal is more ambitious than that of maintaining fitness, say you’re preparing for an endurance event such as a marathon, you may need to increase exercise frequency to as many as 5 or even 6 days per week. ‘Experienced endurance athletes,’ Watson tells us, ‘train daily and sometimes more often than once per day.’

It could well be asked though, wouldn’t such a high-frequency training programme put you at risk of injury? While some studies show that ‘training for 5 days per week may increase injury risk,’ the level of risk can be attenuated if the other fitt principles are adjusted to compensate.

‘It is important to ensure that training takes place at least three times a week. […] Once the body becomes fitter, it is possible to increase the number of weekly sessions from three to four, five or even six. However,’ to avoid injury, ‘some sessions will need to be far easier than others,’ (Royal Marines Fitness).

FITT Principle #Intensity

Training intensity is expressed by how much effort is expended during exercise. Intensity can be measured both qualitatively and quantitively.

For example, the Rate of Perceived Exertion (or RPE) scale is a simplified subjective measure of approximating effort. Often used by fitness trainers to gauge the intensity at which a client is working, intensity is graded against a 10-point scale: 1 being minimum effort (walking) and 10 all-out maximum intensity (sprinting).

Rate of perceived exertion

However, the RPE scale has its limitations. For instance, subjective interpretation of exercise intensity is likely to be both inaccurate and wide of the biological mark. An inexperienced exercise’s perception of what constitutes high intensity will differ from that of a professional trainer’s perception.

In addition, there is a multitude of variables that could influence the exerciser’s perceived exertion rating – mood, energy levels, and training efficacy.

Heart rate

A more accurate method of measuring intensity is using percentages of maximum heart rate (HRmax). ‘Using heart rate as a method of measuring exercise intensity is one of the most common training strategies,’ (National Strength and Conditioning Association).

But because heart rate is directly related to aerobic fitness, it is ineffective for gauging exertion during resistance training. Load or a percentage of one-rep max would be used to interpret intensity in such training situations.

Why training intensity is important

If we always train at a low intensity our fitness is unlikely to improve and we will remain the same. Improved fitness ‘occurs when a part of the body is worked harder than normal.’ When we exercise at higher intensities for sustained periods ‘biological changes then occur and fitness is increased,’ (Physical Fitness & Athletic Performance).

For example, if you want to increase the strength of a muscle, loads must progressively get heavier. By placing additional demands on the muscle beyond what it is used to, strength gains will eventually follow.


An increase in muscle activation ‘provides the primary stimulus to initiate skeletal muscle growth (hypertrophy),’ (Exercise Physiology). Over time this adaptive biological process can result in improved physical performance. And as Watson reminds us, the ‘training effect’ – or hypertrophic rate – is more pronounced if we workout at a higher intensity.

The importance of training intensity is summed up succinctly in the Royal Marines Fitness Manual. ‘Fitness,’ we are told, ‘will not improve unless the body is worked hard enough that it needs to adapt. It is important to up the intensity enough to ensure gains.’

FITT Principle #Time

The first ‘T’ in the fit principle prompts us to reflect on the time or duration of our training sessions. How long we spend working out can impact the training effect. That is, the degree of development we experience from exercising.

But training time is a confusing and contentious principle. For example, is it more effective to workout for shorter durations at high intensities or longer durations at lower intensities?

The old assumption is that the more you put into training the greater the improvement. However, recent studies have challenged this assumption. It’s been argued and demonstrated that frequent long training bouts not only increase injury risk but can also slow or even reverse physical development.

Exercise causes micro fibre tears

This is not surprising when you remember that exercise is a destructive process that results in damaged muscle tissue – micro fibre tears. The more time we spend exercising the more micro tears occur.

If damaged muscle tissue is not given adequate time and nutrition to recover, its ability to repair and grow new tissue will be impeded. The result is physical stagnation or reversal.

‘Training periods that are too long or too intense, and recovery periods that are too short, inhibit […] adaptations and may even result in tissue breakdown, (Physical Fitness & Athletic Performance).

So, what’s the optimal training time?

As with frequency and intensity, the optimal training time is largely dictated by your fitness goals and exercise discipline. Those seeking to maintain a moderate level of fitness might benefit from training durations ranging between 30- to 45-minutes. Whereas the individual preparing for an endurance event, such as an Ironman, may train for as long as 2- to 4-hours.

In preparation for an event, professional Grand Tour cyclists spend upwards of 6-hours in the saddle. In contrast, a CrossFit competitor may workout for as few as 15-minutes – but do so multiple times throughout the day. Short training bouts are more suited to maximal exertion disciplines, such as sprinting, shot put, or powerlifting.

However, irrespective of your fitness goal, to see physical improvements, the time you spend training will gradually need to increase. If the aerobic or muscular systems are not adequately stressed, adaptations will not take place. Thus, to facilitate physiological adaptations the boundaries of training frequency, intensity, and time must be pushed.

FITT Principle #Type

Few people question the type of training or exercise they engage in. Rare is it that an exerciser asks why am I training this way? Or, why are my workouts weighted towards resistance exercises? This is a mistake and one that can impede physical development. Also, failing to match the correct type of training to a specific fitness goal can decrease our chances of obtaining the goal.

To exemplify the point, we would readily identify the mistake made by the person that, having decided to make their training goal improve aerobic fitness, spent most of their workouts in the weights room. The type of training method and exercises selected must accord with the fitness goal.

The type of exercise must reflect the fitness goal

Put succinctly, ‘any training programme developed must be based on the foundations of the required fitness goals. For example, a top rugby player does not want a training programme to prepare him for a marathon. A training programme must contain the types of activities and exercises that will develop fitness needed,’ (Royal Marines Fitness).

But what if you are not pursuing a specific fitness goal, what type of training should you focus on? ‘If the aim of the training is merely non-specific improvement in general physical conditioning, perhaps for health reasons, then almost any form of continuous exercise is capable of improving cardiovascular function,’ (Physical Fitness & Athletic Performance).

However, if you’re looking to cultivate a physical aptitude similar to a CrossFit competitor, you will need to incorporate a broad range of training methods and exercises in your regime.

A simple way to achieve this is to participate in circuits and functional fitness workouts such as those that feature throughout the Hungry4Fitness Book of Circuits and Workouts Volume 2.


F.I.T.T Principle | In Conclusion

The fitt principle can help us to develop a more effective training programme. If applied correctly, FITT can shed light on training weaknesses. For example, using the four components of FITT – frequency, intensity, time, and type – prompts us to ask the following questions:

Frequency: Am I exercising frequently enough to achieve my fitness goal? Should I be training more often throughout the week? Am I overtraining?
Intensity: Do I vary the intensity across my workouts? Am I always training within my comfort zone? Could I train harder?
Time: Is the duration of my workouts sufficient? Should I spend more time per session exercising? How much of my training time is spent sweating as opposed to texting or talking?
Type: Have I selected the most appropriate training method for my fitness goal? Are my workouts populated with exercises that promote the desired training effect?

By asking then answering these questions, the fitt principle encourages us to challenge our training routine. When a weakness has been identified, the above overview of each component of FITT will enable you to make the necessary improvements.

This process will eventually result in an effective training programme that can more effectively bring about desired fitness outcomes.


Related: Discover 10 Benefits of Exercise


In this text box it says: As we are very interested in user experience here at Hungry4Fitness, we would be very grateful if you could take a few seconds out of your day to leave a comment. Thanks in advance! Blog Author: Adam Priest, former Royal Marines Commando, is a personal trainer, lecturer, boxing and Thai boxing enthusiast.

283 views0 comments


bottom of page