To change the training state of an athlete, they need to train more than they are accustomed to. However, for the adaptation to reset to a new and improved training state, a recovery period is required after the overload.
Adaptation
Canadian biologist and endocrinologist Hans Selye described how people react to stress as the General Adaptation Syndrome (GAS). According to Selye, the body has a three-stage response to stress (alarm, resistance, and exhaustion), which can relate to training (Baechle & Earle, 2013).
When a new stimulus or stressor is experienced, the body is alarmed, changing the performance state or homeostasis, a reduction in performance is expected. A decrease in performance marks the alarm phase because of the change in a training stimulus, or stressor is challenging and unaccustomed to the athlete.
The body slowly adapts to the new stress during the resistance phase. The adaptation occurs to the new stimulus, returning the athlete to the previous level of homeostasis despite the challenging training.
Finally, if the stress persists, the body will reach the exhaustion stage. The exhaustion stage is a mismatch of challenging training loads and improper recovery.
However, if after the resistance phase, the stress is reduced before exhaustion, the body will adapt to a new level of resistance, changing homeostasis after a recovery period.

Adaptation To Training
The body changes to a new baseline state after a recovery period from an overload in training. Every athlete has a baseline physical state; the baseline state will change by an overload in the training dose. After a training dose beyond what the athlete is accustomed to, the body gets fatigued or overloaded.
Learn more about The Overload Principle
To adapt, athletes need to recover from a training stimulus. Adaptation is the process of adjusting to the demands of a training program through repeated doses of exercise. The rate of adaptation is determined by volume, intensity, frequency, and exercise selection.
After an overload, to stimulate an adaptation, the most frequently used method is an adjustment (reduction) in the volume during a recovery period. Every athlete responds and adapts to training differently; programs must be individualized to account for varying adaptation rates. The demands of the exercises selected plus the physiological response will help the coach build the adaptation protocol into the program; however, the factors that result in an adaptation will vary with each athlete.
Overload + Change in the Stimulus (Recovery) = Adaptation
Recover and Adapt
The number of training sessions per cycle will have an impact on the outcome of a training program. Training frequency often varies from 3-12 sessions per week, depending on the microcycle plus individual physiological and psychological responses to workouts.
The structure of the program and intensity should remain relatively constant throughout the year with a reduction in volume as the main stimulus for adaptation.
The frequency of maximal intensity sessions must be kept to a minimum because of the recovery needed for the neuromuscular system. Typically 48-72 hours between maximal intensity sessions are required for recovery throughout the year, longer recovery periods may be necessary during the peak phase.
For adaptation to occur, coaches can decrease the load of the program by adjusting the density of the program. Reducing the total volume of training by 30-50% by adding more recovery time between intense sessions will provide the restoration needed for adaptation in most cases.
Besides adjusting the overall volume during recovery periods (3-5 days), the coach can also change the exercises in the program, reduce the intensity of training by at least 30% and add recovery methods to help the athlete recover between training cycles.
In the article How Much Training is Enough? The Overload Principle, other changes besides intensity and volume to stimulate adaptation were mentioned, including:
Switch exercises with similar physiological or physical movements
Adjustments to the recovery period: change timing between sets or exercises
Change in exercise rhythm: adjust the timing in the eccentric phase or concentric phase
Change the sequence of exercises: design a program with a different exercise order
Combine exercises: perform two exercises together (contrast training)
A reduction in the volume of quality training is achieved by lengthening the number of recovery days between high intensity sessions.
Typical Training Cycles
Changing the program every three to four weeks is typical when designing a program. Three weeks of progressive overload followed by a reduction in training volume is common in today’s program. However, some training systems use other methods to create adaptation such as changes in density and structure.
Training Programs
Accurate record keeping can help determine what training methods and exercises will result in the best individual response for each athlete. When the best training combinations or system for an individual is clear, the coach can repeat these methods during the peak phase of the season. It is recommended to test the training cycle considered the best for peaking at least twice before finalizing the program during the final phase of the season.
Predicting the impact of training can be limited, but tracking the key variables in a program can help determine when changes are needed. If the key variables drop off more than anticipated, it is time for a recovery period. Most programs may see a drop off ranging from 5 to 7% during week three, if there is more than a 10% drop off, a change in the program is needed.
Athletes are often below an optimal level in training because of the magnitude of work; however, after a short period of recovery to allow for adaptation, higher levels of performance can be achieved due to more training density. Coaches should not fear a drop off in training during difficult training phases unless the drop off is more than expected.
Coaching Adjustments
Changes often need to be made in the training plan based on feedback. Pay attention to the entire training group for signs of fatigue. If the group has a drop off of more than 7%, the coach should consider changing one or more of the variables and reducing the volume for two to three sessions.
Most training programs change every three to four weeks; however, if an athlete is still improving within a training program, staying on the program with small variations is the best practice. If an athlete has multiple training sessions below the expected performance expectations, changing the entire program must be considered. If there is a drop off of more than 5% in the expected performance parameters for three sessions or more, lowering the program’s volume and intensity should be implemented for at least two sessions.
Sometimes an individual might need a day off because of outside factors such as poor sleep, stress at school, or personal issues that are negatively affecting the athlete’s training.
It is best to adjust a few training sessions when athletes are physically depleted or showing signs of overtraining. It is not a good idea to push through a session that might negatively affect the long term plan just because the training session is already written out.
Coaches need to guide the training based on the state of the athlete, coaches should not follow a program because it is written down.
The idea of developing a repeatable system for each athlete should be the result of experimentation and consistent monitoring. Unfortunately, however, athletes could have a different response to the same training depending on the year or because of external factors that may be out of the control of the coach. Since a similar stimulus can result in different results; the program should be flexible to account for individual needs and differences based on the athlete’s most up-to-date physiological and psychological state.
Overtraining
Overtraining: if a training load is excessive, the athlete can be fatigued to the point that a typical recovery period (3-5 days) is insufficient; this is known as overtraining. If overtraining occurs, the training plan would need to be reevaluated to allow the athlete to return to the previous training state.
Short term changes (5-7 days) in volume, intensity or structure plus adding proven restoration methods will help athletes that are overtrained return to proper training more quickly.
Coaching Methods for Adaptation
It is important to continually test and push the limits of training while maintaining the structure of the program design. After an overload period, adaptation will occur because of a change in density, typically volume or intensity. Reducing the volume is the most common method used to rest the athlete to a new higher training state.
Training for strength, speed and endurance are all influenced by adaptation, the article Neuromuscular Adaptations to Exercise states:
The mode of exercise (e.g. strength training or endurance training) influences the type and magnitude of adaptation in the neuromuscular system. For example, if endurance training (high repetition, low load contractions) is undertaken the muscular system will undergo specific changes that target aerobic metabolism and improved fatigue resistance. Strength training (low repetitions with high load contractions), in contrast, will cause muscle adaptations such as increased myofibrillar protein synthesis. As a result muscle size, strength, and power may increase and improve. Read More
https://www.physio-pedia.com/Neuromuscular_Adaptations_to_Exercise
Starting a New Training Cycle
When restarting a new training cycle, it is recommended to start with a different set of exercises from the previous training cycle while maintaining the basic outline of the program. For example, in complex training used by Bondarchuk advocates, all of the exercises in the program are changed at the end of the cycle; however, the structure of the program remains constant. Overload is a result of training density; adaptation is stimulated by exercise variation. In addition, some coaches adjust volume by lengthening the days between high intensity training during different cycles to promote adaptation.
No matter which type of training system is used, with each cycle, the training and exercises should get more specific to the end performance goal.