FITT is an acronym used in exercise physiology to simplify the rationale behind different exercise principles and systems used to achieve a particular goal. Below is the breakdown of the acronym and the relevant guidelines for muscle development.

F –    Frequency (of exercise)
I  –     Intensity (intensity = resistance/ load and reps
T –     Time duration of each exercise & session
T –     Type of exercises (e.g. progressive resistance training within a range of mainly 6-12 repetitions)
Using The FITT Principle for Muscle Development

Frequency of exercise:
Ideally workout each muscle group between once and at the very most twice a week with each primary muscle getting a minimum of 48hours recovery time before it’s put through its paces again.

Why? The answer is: due to the type, volume and intensity of exercise required to induce muscle growth, there is necessary “damage” to your muscle fibres that occurs. Even with 48hour rest periods between working out the same muscle groups you may still end up “over training” the muscles. By over training muscle, growth is stunted as the muscle becomes more and more stubborn to hypertrophy (growth) and prone to injury.

One of the reasons why over training actually stunts growth is due to an number or reasons including the body’s release stress hormones which are counter-productive to sustaining the anabolic state required for muscle growth.

Intensity of Exercise:
At this point you must be aware that the type of exercise for growth is predominantly weight/ resistance based. It’s common sense, right?
In weight/ resistance training INTENSITY is measured by the load or resistance to use. Ideally weight/load/ resistance selection is based on the muscle building repetition protocol which is; using weights that allow you to complete at least 6 and typically up to/ around 12 repetitions before you need a break.
“Occasionally” you can use weight that allows you to only perform between 1-6 reps or even light enough to allow you to complete repetitions within the muscle endurance training range. All in all, the load must be challenging for the repetition range. Remember that the first adaptation in order for a muscle to grow is for it to get stronger, and only when this is insufficient for the muscle to be at ease with the workload will your body’s different systems work at reinforcing muscle fibres by making them larger.

Time of exercise:
I come across thousands of guys who, in a bid to transform their physiques spend hours upon hours in the gym but to no avail. Simple truth is that marathon-style weight lifting sessions are absolutely unnecessary! No matter how much of a “pump” you get during your workout, YOU DO NOT GROW IN THE GYM! You grow whilst you are resting and recovering. The idea of 2 to 3 hour workouts is mostly counter- productive as you could end up restricting the post-exercise hormonal release which is responsible or priming your muscles to grow.
The truth is only 45 to 60 minutes is appropriate. The advanced/ conditioned athlete could possibly be able to handle durations of up to 90 minutes however it’s not for everyone.
You should always workout with intensity, vigor and focus. Chances are if you are spending a couple of hours per session, your workouts are not as vigorous as they could be. If that’s the case then you need to crank them up!

Type of Exercise:
The best “type” of training for muscle growth is progressively-overloaded resistance training following the F.I.T (frequency, intensity, time) principles above. “Progressive overload” is the gradual increase of stress placed upon the body during exercise training. Progressive overload not only stimulates muscle growth, it also stimulates the nervous system which aids in the development of stronger and denser bones, ligaments, tendons, and cartilage.