Scientific Rules That Lead to Fitness

Squat Overhead Press

Verywell / Ben Goldstein

Table of Contents
View All
Table of Contents

In the study of exercise science, several universally accepted scientific exercise training principles should ideally be followed to get the most from exercise programs and improve physical fitness and sports performance.

These rules are general fundamental principles of exercise science and apply to all athletes, from beginners to elite competitors. Of course, you don't need to follow every one of them all the time. Many people want to get in better shape, improve sports performance, get better at a particular fitness discipline, or avoid stalling and back-slides. In that case, these fundamental rules are the hidden force behind the ability to change your fitness level, according to exercise science.

To design an optimal exercise program, workout, or training schedule, a coach or athlete should adhere to the six fundamental principles of exercise science. Below is more on each of the six principles.

Individual Differences

The principle of individual differences simply means that, because we all are unique individuals, we will all have a slightly different response to an exercise program. This is another way of saying that "one size does not fit all" when it comes to exercise. Well-designed exercise programs should be based on our individual differences and responses to exercise.

Some of these differences have to do with body size and shape, genetics, past experience, chronic conditions, injuries, and even gender. For example, women generally need more recovery time than men, and older athletes generally need more recovery time than younger athletes.

With this in mind, you may or may not want to follow an "off the shelf" exercise program or class and may find it helpful to work with a coach or personal trainer to develop a customized exercise program. Some things to consider when creating your own exercise program include the next batch of exercise science principles.


The exercise science principle of overload states that a greater than normal stress or load on the body is required for training adaptation to take place. What this means is that in order to improve our fitness, strength, or endurance, we need to increase the workload accordingly.

In order for a muscle (including the heart) to increase strength, it must be gradually stressed by working against a load greater than it is accustomed to.

To increase endurance, muscles must work for a longer period of time than they are accustomed to or at a higher intensity level. This could mean lifting more weight or doing ​high-intensity interval training workouts.


The principle of progression implies that there is an optimal level of overload that should be achieved and an optimal time frame for this overload to occur. A gradual and systematic increase in the workload over a period of time will result in improvements in fitness without risk of injury.

If overload occurs too slowly, improvement is unlikely, but overload that is increased too rapidly may result in injury or muscle damage. For example, the weekend athlete who exercises vigorously only on weekends violates the principle of progression and most likely will not see noticeable fitness gains.

The Principle of Progression also stresses the need for proper rest and recovery. Continual stress on the body and constant overload will result in exhaustion and injury. You should not train hard all the time, as you'll risk overtraining and decreasing fitness.


Adaptation refers to the body's ability to adjust to increased or decreased physical demands. It is also one way we learn to coordinate muscle movement and develop sports-specific skills, such as batting, swimming freestyle, or shooting free throws.

Repeatedly practicing a skill or activity makes it second-nature and easier to perform.

Adaptation explains why beginning exercisers are often sore after starting a new routine, but after doing the same exercise for weeks and months, they have minor, if any, muscle soreness. Additionally, it makes an athlete very efficient and allows him to expend less energy doing the same movements. This reinforces the need to vary a workout routine to see continued improvement.


The Principle of Use/Disuse implies that when it comes to fitness, you do actually  "use it or lose it."  This simply means that your muscles hypertrophy with use and atrophy with disuse. This also explains why we decondition or lose fitness​ when we stop exercising.


We've all heard the phrase, "practice makes perfect." Well, this is the principle of specificity in action. This principle states that exercising a specific body part or component primarily develops that part. The principle of specificity implies that to become better at a particular exercise or skill, you must perform that exercise or skill.

A runner should train by running, a swimmer by swimming, and a cyclist by cycling. While it's helpful to have a good base of fitness and do general conditioning routines, if you want to be better at your sport, you need to train specifically for that sport.

A Word From Verywell

These six basics are the cornerstones of all other effective training methods and cover all major aspects of a solid foundation of athletic training. Designing a program that adheres to all of these guidelines can be challenging, so it's not a surprise that many athletes turn to a coach or trainer for help.

1 Source
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Flores DF, Gentil P, Brown LE, Pinto RS, Carregaro RL, Bottaro M. Dissociated time course of recovery between genders after resistance exercise. J Strength Cond Res. 2011;25(11):3039-44. doi:10.1519/JSC.0b013e318212dea4

Additional Reading
  • Wilmore, J.H. and Costill, D.L. Physiology of Sport and Exercise: 3rd Edition. 2005. Human Kinetics Publishing.

By Elizabeth Quinn, MS
Elizabeth Quinn is an exercise physiologist, sports medicine writer, and fitness consultant for corporate wellness and rehabilitation clinics.