Specificity, progressive overload, reversibility, adaptability, individuality and recovery time: what each principle does physiologically, and how to apply it when you write a programme.
Glenn Coburn
Tutor & S&C Coach · 5 June 2024 · 10 min read
Reviewed by
Lewis Coldham
Four years in injury rehabilitation at West Ham United Academy
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Fitness is not a one size fits all venture, it is a personalised journey that varies from one individual to another. Whether you are an athlete, a fitness enthusiast or a health conscious individual, it is essential to understand the physiological principles of fitness training that underlie effective training.
Before looking at any of these principles, however, the first step to effective programme design is a thorough consultation. The programme you write for a client should be based on the information you have gained from them.
This is exactly what Create’s L3 Personal Training course trains you to do. Module 3 alone dedicates over an hour of content to health screening, fitness assessment, and the communication skills needed to turn a client consultation into a programme that actually gets followed.
That covers their routine, training history, availability, age and a load more variables, but most importantly their goals. You could write the best programme in the world, but if it is not built around your client achieving their goals they are very unlikely to stick to it.
These principles include Specificity, Progressive Overload, Reversibility, Adaptability, Individuality, and Recovery Time. Each one is covered below with its physiological implications and how to apply it, so you can better tailor your training programme.
One of the cornerstone principles of effective training is Specificity. This principle states that training should be tailored to the specific demands of the activity you are preparing for. A marathon runner would focus on long distance, low intensity training, while a sprinter would focus on high intensity, short bursts of exercise. The physiological impact is significant. Your muscle fibres, energy systems and motor skills all adapt in highly specific ways based on the type of training you undertake.
Example: imagine you are a basketball player working on your jump shot. Practising long distance running will not be as beneficial as exercises that improve your vertical jump, such as plyometrics or box jumps. That specificity ensures the muscles and motor skills you need for your sport are the ones being developed.
The main takeaway with applying specificity is to make sure the gym work you are doing fits your goals, or your client’s, but to leave the highly specific training to the sport itself and use the gym work to complement and improve the sport.
The problem with specificity is that some people focus too much on it. If you are training for a sport, the most sport specific training you can do is the sport itself. Gym work should enhance the athlete's ability to perform, and the best way to do that is not necessarily through movements that closely mimic the sport. Take rugby: building muscle mass and overall strength is key to being good at it, but the training that builds them looks nothing like throwing or kicking a ball.
Progressive Overload is the idea that the body only adapts when it is challenged beyond its existing capabilities. As you become more comfortable with your routine, the intensity has to rise for results to continue. The physiological implications include increased muscle mass, improved cardiovascular function and enhanced neural pathways for movement.
Example: you start squatting with 50kg on the barbell and find it challenging. As your strength improves, 50kg becomes easier, so to keep making gains you move to 60kg, keeping the muscles challenged.
There are multiple ways to apply progressive overload. The most obvious is to increase the weight or the reps in resistance training, and to increase speed or duration in cardio. Others include using variations of the exercise, reducing rest, increasing range of motion, increasing training frequency or volume, or increasing time under tension. All of them make the exercise gradually harder over time, although we would recommend sticking with weight and reps until you start to plateau, then introducing other variables.
Progressive overload sounds simple in theory, but knowing how to apply it correctly, when to increase weight versus reps versus tempo versus rest, is a skill that takes structured learning.
Module 4 of Create’s L3 Personal Training course dedicates 44 minutes and 17 assessed questions to exactly this, covering the full principles of programme design so you can apply overload intelligently for any client, not just yourself.
Remember the saying “use it or lose it”? That is essentially the Reversibility principle. If you stop exercising, or significantly reduce the intensity and frequency of your workouts, you will lose the gains you have made. Physiologically that can mean muscle atrophy, a decrease in cardiovascular efficiency and a slowdown in metabolic rate.
Example: consider someone who was an avid runner but had to take a break because of an injury. After a few months of no activity they find they cannot run as fast or as far as they used to, which is reversibility in action.
You will likely not go back to square one, and another cliche is at work here: it is like riding a bike. That is down to a phenomenon called muscle memory. Someone who has previously been well conditioned can be retrained more easily following a period of inactivity, mostly because of motor learning in the central nervous system, which lets the body recall previously learned movement patterns.
That does not explain why it is easier to regain muscle force and size when returning to strength training. Recent research shows that muscle hypertrophy and atrophy are not completely reversible processes.
When muscles grow in size and strength, additional myonuclei are added to the muscle fibres. When the muscle atrophies, there is no evidence that the myonuclei reduce in number, so on returning to strength training the previously recruited myonuclei are already in place and speed up the return of strength and size.
The human body is remarkably adaptable and capable of adjusting to a wide range of conditions and stimuli. Whether you are an athlete preparing for a high altitude event or someone adjusting to a new type of exercise, your body undergoes physiological changes to meet the new demand. Those changes might include improved oxygen carrying capacity or increased red blood cell production.
Example: you have always been a runner, but you decide to take up swimming. At first it is a struggle, because different muscles are involved, but after a few weeks it becomes easier. Your body has adapted to the new form of exercise.
You may have heard of the 10,000 hour rule, which Malcolm Gladwell refers to in his book Outliers. It is used to illustrate how long it takes to become an expert at something, the key being practising that activity over and over, correctly, for around 10,000 hours. Over time you ingrain movement patterns and motor skills that let you master an activity. That improvement over time is adaptability at play.
Everyone’s body is different, so responses to fitness training vary widely between individuals. Some people make rapid gains in strength, while others find endurance activities come more naturally. This principle is why customised programmes, tailored to an individual’s physiology, are generally more effective.
Example: two friends start a weightlifting programme together. After a month one notices significant gains in muscle mass, while the other sees more improvement in endurance. Their bodies respond differently to the same stimulus.
This principle can make certain individuals more genetically predisposed to being good at certain activities. If you struggle to improve your endurance capacity, marathon running may not be your best choice if you want to excel. Equally, if building muscle mass comes fairly easily to you, bodybuilding or powerlifting may be a great choice of sport. It does not mean you are destined to be bad at something you are not naturally gifted at, only that it may take more hard work over a longer period.
Designing a truly customised programme takes more than understanding physiology. It takes knowing how to communicate with clients, identify what motivates them, and adapt your approach when they struggle to stay consistent.
Module 3 of Create’s L3 Personal Training course dedicates nearly an hour of content across two topics, Communication to Encourage Positive Health and Fitness Behaviours, and Behaviour Change Techniques, teaching you the human side of personal training that turns a good programme into one clients actually stick to.
Recovery is not just about catching your breath after a strenuous workout, it is a critical component of physiological improvement. During recovery, damaged tissue repairs, metabolic waste is cleared and energy stores are replenished. Ignoring it can lead to overtraining, which can suppress the immune system and raise the risk of injury.
Example: an experienced cyclist who trains hard without adequate rest days starts to notice a decline in performance and frequent colds. That can be a sign of overtraining and of the body needing recovery time to repair tissue and support the immune system.
Tangible signs such as fatigue or illness make the need for rest obvious, but the problem with waiting for them is that by then you have left it too late. For beginners, build intensity and volume gradually to build tolerance and to work out their own requirement for rest. More advanced athletes can be the harder case, because their love of the sport and their desire to improve leads them to neglect rest, so your job as a coach is to build a well structured programme with adequate rest in it.
Understanding these physiological principles of fitness training can drastically improve the effectiveness and efficiency of your training programme. They offer tailored solutions that cater to your individual needs, helping you get the most out of each workout. Whether you are new to fitness or a seasoned athlete, these principles are essential to achieving your goals in a healthy and efficient manner. If you want to go deeper, our online personal training courses cover each of these principles in far more detail, along with the knowledge and skills to apply them to real clients.
Restructured into blocks. The six principles were promoted from H3 to H2 so the automatic contents list renders, key takeaways and an FAQ were added, and the three course links were repointed from the retired /fitness-qualifications/ path to the current course URL. No section was cut and no heading was reworded.
Glenn Coburn
Tutor & S&C Coach
Glenn has 15 years in the fitness industry and has been tutoring and assessing since 2013, including as Curriculum Manager at YMCAfit. He holds a degree in Health and Fitness and Level 4 qualifications in both Strength and Conditioning and Nutrition.
Reviewed by Lewis Coldham, Four years in injury rehabilitation at West Ham United Academy.
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