Fatigue is an expected and desired part of the training process. As expected, it reflects the athlete’s reaction to the training stress, which is very demanding from the physiological and psychological perspective. 
Tennis play is pretty complex combination of the movement patterns which brings the players to the strategic position (towards the ball or related to the opponent) and the decision making process of stroke execution and the reaction. Based on that, fatigue shouldn’t be regarded as the one dimensional physiological outcome of the training process. The efficiency of the tennis performance is relying on the cognitive ability of the player. Even if player is at the optimal position, the mistake can be caused by psychological dimensions such are lack of concentration, poor decision making or lack of self confidence.
Fatigue is a decrease in the athlete’s capacity to perform at the high level. Ensuring optimal performance is directly proportional to reducing or delaying the onset of fatigue as much as possible. But, from the perspective of the measuring the training stress to the recovery ratio, acute fatigue is a desired part of the training process as it can be a marker of the current athlete’s response to the training session load. Knowing the level of fatigue, the coach can manage every part of the practice successfully.
Types of fatigue
Managing the relationship between the training stress and the fatigue is a complex process. There are many sources of fatigue and therefore fatigue shouldn’t be perceived as one dimensional element of the training process. To be able to understand the fatigue, coach and player have to be equipped to identify the source of it. If they are able to identify the sources and type of fatigue, the efficient type of recovery strategy can be applied and therefore successful adaptation and recovery period. Depending on the type of exercise, different type of fatigue can influence the athlete’s response.
Metabolic fatigue is a type of fatigue with the source such is imbalance between the energy spent and the energy required to perform (usually imbalance in the nutritional input and output (fluids and fuels)). The energy stores are depleted after the high volumes of training and competition, following the inadequate nutritional restorations of the energy systems. The player shows signs of fatigue sooner then expected and have difficulties to complete the training session.
Neural fatigue may result from fatigue of the peripheral nervous system (PNS) and the central nervous system (CNS). PNS (muscle) fatigue is situated exclusively in the skeletal muscles. It may occur after short but high intensity training sessions. The player is showing signs of the slow reaction at the court, have difficulties to create enough stroke power and having inconsistent stroke technique. CNS (neural) fatigue occurs due to the long training sessions demanding the fast reactions and decision making. Usually the cause is the decrease in the glucose levels (mind and body’s fuel) as the player has hard time to concentrate and keep the motivation level high. Neural fatigue usually occurs when the player has an inadequate diet, lacks motivation, sleep and rest or is injured. The most often causes are nutrition and the psychological fatigue.
The causes of psychological fatigue are internal and environment pressure and stress from the competition, event, parents, school etc. Players are usually experiencing low self confidence levels and building the negative attitude towards the environment and their performance. The body language and self talk is a reflection of their negative thoughts and psychological fatigue.
Environmental fatigue can occur due to the time spent traveling and dealing with different climate conditions and time zones. These can develop the conditions of disruptions in normal training and living routine such are disturbed in sleeping and waking up times, meal times etc. The player playing in hot conditions, which is not used to, could experience the signs of fatigue in the early stages of the practice or match. Due to the higher humidity conditions, the player can experience raising in body temperature which directly influences the decrease of performance.
The fatigue in tennis is likely to affect physiological functions (cardiovascular fitness, thermoregulation, neuromuscular function, endocrine function) and tennis-specific physiological functions and stroke execution (shoulder rotator cuff strength, muscular strength, serve velocity and accuracy etc).
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