3 Key Principles of Fitness for Your New Routine
By Dr. Kayla Frost (DPT, PT)
The 3 Key Principles of Fitness
When starting a new exercise routine, there are a few fundamental concepts that you should know about and apply. These concepts are the:
1. Specificity principle
2. Overload principle
3. FITT principle
These three guiding concepts can help you establish a strong foundation for your new exercise program.
Specificity Principle (SAID Principle)
The specificity principle is also known as the SAID principle, which stands for “Specific Adaptations to Imposed Demands.” The specificity principle states that the body will develop specific adaptations to the type and duration of the exercise performed. For example, if you want to improve your endurance, you would benefit from low-load aerobic activity for longer durations of time. If you want to get stronger, you will want to challenge your strength by lifting heavy objects. Put simply, how you train should mimic the skills you want to acquire.
Overload Principle
To improve any aspect of physical fitness, the individual must continually increase the physical demand placed on their body. This is called the overload principle. The overload principle posits that an exercise must be challenging in order for adaptations to occur. Take a biceps curl, for example. When performing a biceps curl, if the load is greater than the force that the muscles are used to producing during a contraction, micro-tears develop in the muscle fibers. With rest, those tears repair, the muscle cells become larger than they were before, and the muscles get stronger (this is called muscle hypertrophy). Without the increased load (overload), the muscle fibers will not tear and you will not get an adaptive growth of the muscle.
The FITT Principle
One of my favorite resources in exercise programming that helps to systematically overload the body is called the FITT principle. The FITT principle is a simple framework used to increase your workout volume and progress your training.
The effectiveness of a fitness plan depends on several key elements of exercise. The American College of Sports Medicine (ACSM) suggests the use of the FITT principle to remember these key elements.1 FITT stands for “frequency, intensity, type, and time.” Without these elements, no program would be complete.
Frequency
Frequency is the number of days per week dedicated to an exercise program. The optimal frequency may depend on the level of fitness and age of an individual, as well as the intensity of the program. For example, training at a lower intensity with a greater frequency may be beneficial to improve coordination in those that are new to exercise, while training at higher intensity and lower frequency may benefit those trying to gain muscle mass. More recovery time between bouts of exercise is often needed when training at higher intensities.
For most adults, ACSM recommends moderate intensity aerobic exercise at least 5 times per week, or vigorous intensity aerobic exercise at least 3 days per week. I personally believe that everyone should make a goal of getting some kind of exercise every single day. This is because the human body evolved to move frequently on a daily basis in order to acquire food for survival. Resting in a sitting position all day will contribute to weakness and tightness, especially in the hips and back. I recommend making a habit of doing something for movement every single day, even when resting from more vigorous workouts. A light exercise day can consist of yoga, light weight training in muscles that aren’t sore, or a 30 minute walk. This creates a habit of moving because, as Newton’s Law of Motion says, “a body in motion stays in motion.” On the other hand, the sedentary lifestyle promotes the development of chronic disease and dysfunction, which perpetuates dysfunction. Move more, do more.
Intensity
Intensity is a subjective measurement that refers to how hard you are working and is often measured as a percentage of heart rate reserve (HRR) or VO2max. If you don’t want to do calculations, you can simply use the Rate of Perceived Exertion Scale (RPE), where 1 means minimal difficulty and 10 means maximal difficulty. On the RPE scale, 2-3 is light exercise, 4-5 is moderate exercise, 6 to 7 is hard exercise, and 8 to 9 is very hard exercise.
ACSM recommends moderate to vigorous intensity aerobic exercise for most adults, and light to moderate intensity aerobic exercise for deconditioned adults. Vigorous exercise roughly translates to an RPE 8 and above, while moderate intensity translates to 5-7.
Type
Aerobic and resistance exercises are two types of exercise. Aerobic exercise is usually rhythmic in nature and involves several large muscle groups (i.e. swimming, running, walking, elliptical, and biking). Resistance exercise involves added weight, including one’s own body weight. To improve endurance and cardiovascular function, aerobic and resistance exercises are both good options.
Time
The term “time” refers to the duration of an activity performed. ACSM recommends greater than 150 minutes per week of moderate intensity exercise, and over 75 minutes of vigorous intensity exercise for most adults. Longer durations of activity is often needed to help offset time sitting for sedentary individuals.As I mentioned before, I believe that everyone should make it a goal to do something active for at least 30 minutes every single day. It may take time to work up to this level of fitness for those that are just getting back into exercise. Just know that your body will adapt to whatever you do. If you spend more time running, you will get better at running. If you spend more time sitting, you will get better at sitting (and you will get worse at being healthy).
Conclusion
The most successful changes take place based on the overload and specificity principles. Specific exercise elicits specific adaptations. The overload principle states that adaptations take place when the body is stressed beyond what it is accustomed. In order to progress one’s fitness, the frequency, intensity, type, and duration of an activity must increase over time. Using the specificity, overload, and FITT principles, you can jump-start your exercise routine and set a good foundation for wellness.
Reference:
- American College of Sports Medicine. ACSM’s Guidelines for Exercise Testing and Prescription. Wolters Kluwer; 2018; p 143-162. Accessed March 7, 2023. https://catalog.jcls.org/Record/244090