This is an excerpt from Essentials of Strength Training and Conditioning 4th Edition With Web Resource by NSCA -National Strength & Conditioning Association.
The goal of training is to provide incremental overload on the body so that physiological adaptations can subsequently contribute to improved performance. Successful training must not only involve overload, but must also avoid the combination of excessive overload with inadequate recovery (140). When training frequency, volume, or intensity (or some combination of these) is excessive without sufficient rest, recovery, and nutrient intake, conditions of extreme fatigue, illness, or injury (or more than one of these) can occur (110, 124, 185). This accumulation of training stress can result in long-term decrements in performance with or without associated physiological and psychological signs and symptoms of maladaptation, and is referred to as overtraining. Depending on the extent to which an athlete is overtrained, restoration of performance can take several weeks or months (81, 140).
When an athlete undertakes excessive training that leads to short-term decrements in performance, this temporary response has been termed overreaching or functional overreaching (FOR) (58, 163). Recovery from this condition is normally achieved within a few days or weeks of rest; consequently, overreaching can be prescribed as a planned phase in many training programs. The rationale is to overwork (to suppress performance and build up tolerance) and then taper in order to allow for a "supercompensation" in performance. In fact, it has been shown that short-term overreaching followed by an appropriate tapering period can result in beneficial strength and power gains (163). When mismanaged, however, it can lead to detrimental effects (144).
When the intensification of a training stimulus continues without adequate recovery and regeneration, an athlete can evolve into a state of extreme overreaching, or nonfunctional overreaching (NFOR). This NFOR leads to stagnation and a decrease in performance that will continue for several weeks or months. When an athlete does not fully respect the balance between training and recovery, the first signs and symptoms of prolonged training distress are decreased performance, increased fatigue, decreased vigor, and hormonal disturbances. When those occur, it becomes difficult to differentiate between NFOR and what has been termed overtraining syndrome (OTS). Central to the definition of OTS is a "prolonged maladaptation" not only of the athlete, but also of several biological, neurochemical, and hormonal regulation mechanisms. Many alternative terms have been suggested for OTS, including burnout, chronic overwork, staleness, unexplained underperformance syndrome, and overfatigue (21, 23). Figure 5.6 illustrates the progression that composes the overtraining continuum.
The overtraining continuum.
Overtraining syndrome can last as long as six months or beyond; and in the worst-case scenario, OTS can ruin an athletic career. Two distinct types of OTS have been proposed: sympathetic and parasympathetic. The sympathetic overtraining syndrome includes increased sympathetic activity at rest, whereas the parasympathetic overtraining syndrome involves increased parasympathetic activity at rest and with exercise (140). The sympathetic syndrome is thought to develop before the parasympathetic syndrome and predominates in younger athletes who train for speed or power (58). Eventually all states of overtraining culminate in the parasympathetic syndrome and the chronic suppression of most physiological systems throughout the body (140). Because rebounds are possible, it is difficult to determine exactly when overtraining becomes chronic. In addition, some athletes respond positively to overreaching strategies (163) whereas for others, overreaching can be the catalyst for OTS.
A predominant feature of OTS is the inability to sustain high-intensity exercise when training load is maintained or increased (141). In many cases OTS is a consequence of prolonged NFOR, which in itself can result from mistakes in the prescription of training load and a mismanagement of the acute training variables (e.g., intensity, volume, rest). A common mistake in overtrained athletes is a rate of progressive overload that is too high. That is, increasing either the volume or intensity (or both) too rapidly over a period of several weeks or months with insufficient recovery can result in greater structural damage over time and, potentially, overtraining. A theoretical overview of anaerobic overtraining is presented in table 5.3.
For the purpose of investigating overtraining, deliberately causing OTS is not easy in a laboratory setting. What is more, while the symptoms of OTS are generally thought of as more severe than those of NFOR, there is no scientific evidence to confirm or refute this suggestion (140), making it hard to confirm that OTS has occurred. Instead, longitudinal monitoring of athletes has been the most practical way of documenting the physiological responses and performance effects of overtraining. The majority of this research has been conducted in endurance-type sports, where it is perhaps more prevalent. However, a survey of overtrained athletes showed that 77% were also involved in sports requiring high levels of strength, speed, or coordination (58). The symptoms of overtraining found in anaerobic activities (sympathetic) were also different from those in aerobic - endurance activities (parasympathetic) (23, 58).
Sympathetic-type overtraining is a little more difficult to characterize than parasympathetic overtraining. It can be speculated that increased neural activity consequent to excessive motor unit activation may bring about this type of overtraining; however, there are many other factors that could potentially contribute. Adopting a short-term NFOR model (eight sets of machine squats with a 95% 1RM load for six consecutive days), Fry and colleagues (59) examined intensity-specific responses and reported nonspecific performance decreases in isokinetic torque production, longer sprint times, and longer agility times. They did, however, find that 1RM strength was preserved. In a subsequent study by Fry and associates (62), subjects performed 10 sets of 1RM over seven days with a day’s rest. This resulted in a significant decrease (>9.9 pounds [4.5 kg]) in the 1RM in 73% of the subjects. Interestingly, some subjects made progress and did not reach a NFOR state. This demonstrates that the time course for the onset of overreaching or overtraining symptoms is greatly dependent on individual responses, training status, and genetic endowment.
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