Among chronic exercisers, there is always the potential of doing more but receiving less. What many exercisers do not realize is that additional workouts can sometimes lead to the law of diminishing returns, where anticipated responses do not occur. It has been well established that in order to receive a training effect, the exerciser must experience some fatigue. This fatigue will in turn induce a need for recovery, which leads to a period of overcompensation or the training effect. However, if there is little or no recovery, combined with additional intense activity, the overcompensation or training effects do not occur, and overtraining symptoms can be observed. The term overtraining has been used interchangeably with staleness, burnout, chronic fatigue, stagnation, overwork or run down. Researchers have reported no less than 31 features of overtraining extending to 84. The most prominent features of overtraining include: heavy legs, sore muscles, high resting heart rate, poor motivation, sleep disturbances, low libido, frequent sickness or infection, weight loss, depression and increased rating of perceived exertion.
- Blood Hormones as Markers of Training Stress and Overtraining, Urhausen, A., Gabriel, H., & Kindermann, W. (1995), Sports Medicine. 20 (4): 251-276
The effects of training require a level of intensity that will induce some fatigue, which in turn will cause a need for recovery followed by a period of overcompensation. Beginning the next exercise session at the peak of overcompensation will lead to an accumulation of responses and an improvement in the training state. Successful trainers and coaches will know how to adequately overload the body to the point of overcompensation. However, when overload exceeds the recovering capabilities of the body an overreaching or overtrained state may eventuate.
While overtraining is known to exist, its prior identification is open to debate. While many of the symptoms are standardised, their evaluation is more difficult. Many of the tests recommended lack a degree of specificity for the sports or activities that overtrained athletes may participate in. Some researchers have suggested that monitoring hormonal or substrate levels may be more successful than performance indicators.
The purpose of this study was to examine many of the reported hormones and gauge their role in the overtrained state.
Epinephrine (adrenaline) and Norepinephrine (noradrenaline)
During incremental aerobic exercise, there is a corresponding increase in lactate levels. When the client exceeds the anaerobic threshold, there is marked increase in lactate and hydrogen ions, which create an acidic environment lowering the pH of the body. Epinephrine and norepinephrine levels continue to rise incrementally with the exercise intensity. Above the anaerobic threshold, the hormonal levels dramatically increase above the gradient of the lower intensities. Exercising below the anaerobic threshold for prolonged periods creates a very small difference in the secretion between norepinephrine and epinephrine. Higher intense exercise over a shorter duration shows higher secretion levels of epinephrine and norepinephrine and creates a larger difference between them.
In athletes who are overtrained, disturbed levels of glycogen use with a reduced maximal blood lactate levels have been observed. This is reflected in lower levels of epinephrine and norepinephrine circulating in the plasma after strenuous exercise. However, during exercise, these levels were elevated due to the decreased sensitivity of their receptors.
Identifying overtraining by measuring norepinephrine and norepinephrine is still open to problems. Many of the problems associated with this identification have to do with the blood sampling techniques, repeatability of tests and general methodological procedures.
Testosterone and Cortisol
It has been suggested that overtraining can be recognized by a decrease in the ratio of free testosterone to cortisol > 30 %. It has been observed that changes in this ratio are governed differently in males and females. Changes in this ratio for males is the result of movement of testosterone, while in females it is affected more by cortisol, probably due to its stability during the menstrual cycle.
It appears that changes in the testosterone to cortisol, as an indicator of overtraining are still subject to debate. It appears more likely that the changes that do occur, are more the result of the current training load. Long distance running has been reported to decrease testosterone levels but had little effect on the sperm quality. This did not appear to produce the same effect in high intensity training programs.
Testosterone fluctuates with different types of exercise. In short duration, high intensity exercise, testosterone levels tend to increase due to inability of the liver to clear it quickly, as well as the stimulation of specific receptors in the testes. When the duration increases and the intensity drops, so does the level of circulating testosterone. During the recovery period it has been reported that it may take hours and sometime days to return to pre exercise levels. Researchers have suggested this is due to an increased cortisol suppression of testosterone, decreased blood flow to the testes and the desensitising of the testicular receptors because of reduced prolactin level or an increased pickup of testosterone by the muscles and organs.
Cortisol is the most abundant glucocorticoid in the body and is responsible for promoting normal metabolism, resistance to stress and promote anti-inflammatory responses. This hormone has been mentioned throughout the research as a possible indicator of overtraining, as it mimics exercise intensity and maintains high levels during overtraining. These higher than normal levels have reported in amenorrhoea athletes, suggesting a break down effect.
To measure an increase in cortisol levels during exercise, the duration must be greater than 20 minutes at an intensity of 60% VO2 max. At the completion of the exercise and under normal conditions, cortisol levels drop rapidly and return to resting levels after a few hours. The role of cortisol can also be affected by diet.
Repeated bouts of intense activity for longer durations at an increased frequency can lead to reduced levels of cortisol and corticotrophic stress hormones. This can further lead to decreased ability sodium, potassium and ATPase enzyme. Sodium and potassium movements across the cell membrane are responsible for the initiation and propagation of the action potential down the nerve fibre. To maintain adequate levels across the cell membrane, the sodium potassium pump helps restore this equilibrium. While training enhances the ability of the sodium potassium pump to perform its function, during overtraining it has been reported there is an increase in potassium within the cell. This is partly the result of the sodium potassium pump not performing to its optimal level. This can increase partly explain the muscle complaints often reported in overtraining.
Corticotrophin hormone is responsible for the release of certain hormones from the adrenal glands and is regulated by the hypothalamus. The hypothalamus is located in the brain and controls many functions of the body to maintain homeostasis (body in balance). Corticotrophin hormone secretion is affected by exercise intensity and decreased levels of blood glucose. There has been reported an increase in corticotrophin in trained compared to untrained women. Conversely, lower levels of corticotrophin have been reported in overtrained athletes. This could be due to changes in the sensitivity of chemo-receptors. Overtrained athletes often complain of heavy legs without a concomitant increase in lactate levels possible due to the same mechanism.
Endorphins are released from the brain and have been linked to memory and learning, body temperature, sexual activity, onset of puberty, reproduction, depression and schizophrenia. The release of endorphins is strongly correlated to exercise intensity. A specific threshold needs to be exceeded for the endorphin release to be maximised. There has been some suggestion that intensity above the anaerobic threshold has to be exceeded for up to 60 minutes for the endorphin release to be significant. This would indicate that the greater the involvement of the lactic acid system during the aerobic phase might enhance its release. Overtrained athletes in some studies have demonstrated lower levels of endorphins.
Prolactin, while acting together with other hormones is responsible for the maintenance of milk secretion from the mammary glands. The changes in prolaction during exercise appear to be related to training state, the availability of intracellular glucose and the exercise intensity. High volume training, inducing overtraining did not have any effect on prolactin levels. As a means of monitoring overtraining it appears to be limited.
Insulin is released from the pancreas and decreases blood sugar levels. It accelerates the movement of glucose from the blood into the cells. Overtraining studies have reported lower blood sugar levels, which are indicative of depletion muscle glycogen levels, possibly due to a lowered maximal exercise induced level of insulin.
During training regimes there is normally an increase in hormonal activity. This is in contrast to overtraining studies, which report impaired secretion of the same hormones. Further decreased insulin and cortisol, in combination with lowered testosterone levels can result in a reduction in protein synthesis and glycogen repletion during the recovery phase.
During muscle glycogen depletion, the body maintains its fuel source by gluconeogenesis. This occurs when the muscle converts protein as an energy source by utilising branch chain amino acids as a main fuel. The use of branch chain amino acids increases the levels of tryptophan. The increased circulating tryptophan increases seratonin levels in the brain and is regarded as a main cause of central fatigue. While it might be possible that this increase in seratonin can increase fatigue, it might be premature to assume it as major contributor to overtraining.
- Pituitary -Adrenal-Gonadal Responses to High Intensity Resistance Exercise Overtraining, Fry, A. C., Kraemer, W. J., & Ramsey, L. T. (1998), Journal of Applied Physiology. 85: (6) 2352-2359
Overtraining in aerobic exercise is well documented. Clearly it is emphasised as a decrement in performance usually caused by injudicious amounts of high intensity exercise without adequate recovery. It appears that when comparing anaerobic activity to aerobic activity, the concept of overtraining could be quite different. It is also possible that different types of resistance training programs could induce different types of overtraining. In aerobic exercise, some studies have used endocrine changes to indicate states of overreaching and overtraining. In resistance training, these results are not as reliable, as many of the endocrine analyses have been monitored during resting conditions.
The purpose of his study was to determine whether overtraining using a high intensity resistance training protocol can alter circulating hormonal levels.
Eleven well-trained weight trained males volunteered for this study. The sample was divided into a training group and a control group. The training group performed a daily 100 percent one-repetition maximum on 10 exercises for two weeks. A control group trained once per day at a low relative intensity (50 percent RM). Blood sampling was taken at regular intervals measuring total testosterone, free testosterone, cortisol and growth hormone.
The overtraining group increased strength significantly by approximately 11 percent compared to the control group. Testosterone, free testosterone and growth hormone showed slight increases for both the overtraining group and the control group. Testosterone levels were elevated immediately after the exercise session in the overtraining group, while the control group showed increases at rest and immediately after training. There was no increase in cortisol for either group during or after the training regimes. Growth hormone concentrations were the same for both groups. There was no change in resting levels of pituitary, adrenal or gonadal hormones for either group.
Application for the Fitness Instructor
- The overtraining group in this study demonstrated significant decreases in performance in a one-repetition maximum leg strength test. The decrease in performance lasted up to eight weeks and was only overcome by a long recovery period. Interestingly, this apparent overtraining was not reflected in changes in creatine kinase or muscle soreness. In this study, the upper body exercises was held constant over the two week exercise period, while the lower body was under constant high intensity overload. Consequently, the upper body did not demonstrate overtraining, while the lower body did. It may be that the monitoring of hormonal responses in resistance training is not a valid marker for identifying overtraining. It may have been that the overtraining protocol was not intense enough or volume loaded enough to activate testicular or adrenal cortex activity in activating hormonal responses.
- Total testosterone concentrations slightly increased in the overtraining group. This was partly due to an increased secretion and decreased clearance of testosterone. Free testosterone and cortisol did not appear to be affected by the overtrained state.
- In some studies a change in the ratio of testosterone to cortisol has been recommended as a marker for identifying overtraining, particularly in endurance training. This was not the case in high intensity resistance training induced overtraining, where this ratio appeared not to predict overtraining. Perhaps different overtraining markers need to be considered for different exercise regimes.
- Overtraining in Endurance Athletes: A Brief Review, Lehmann, M., Foster, C., & Keul, J. (1993), Medicine and Science in Sports and Exercise. 25 (7): 854-862
While overtraining has been known for many years, many problems have existed in identifying its markers. The causes of overtraining are many and varied including factors directly associated with the training program, the homeostatic state of the athlete and the sport or fitness activity causing the overtraining.
The purpose of this study was to examine overtraining markers that are specific to endurance training.
It is important to draw a difference between short term overtraining and long term overtraining. Short term overtraining usually lasts between a few days to possibly two to three weeks, while long term overtraining can last from a few weeks to several months. The common thread that both forms of overtraining have is the need for adequate recovery to combat the problem.
Short term overtraining often manifests itself as fatigue, reduced performance at the anaerobic threshold and poor performance in competition. Usually two weeks of rest restores the athlete back to a competitive state. The problem that can compound overtraining, is the reaction of coaches and athletes to solve a form slump by training harder and longer. This practice can convert short term overtraining to long term overtraining, where the previously identified symptoms can take many weeks or even months to overcome.
Short term overtraining is often seen as peripheral fatigue, while overtraining is referred to as a more deep-seated central fatigue. The importance of fatigue cannot be understated, as it is the body’s recognition that recovery is needed to enhance the training completed. In many ways, it becomes a protective mechanism to prevent long term damage that can result in chronic fatigue symptoms. This can be seen as a decrease in receptor sensitivity, heart rate changes at rest, increased levels of tryptophan (amino acid), elevated activity of y-aminobutyric acid (a brain inhibitory neurotransmitter) and possible partial pituitary and hypothalamic gland dysfunction. The hypothalamus is found in the brain. Its main function is the regulation of many bodily functions resulting in homeostasis (body in balance).
Classical and Modern Forms of Overtraining
Classical overtraining is often referred to as sympathetic overtraining and while regarded as rare is seen in anaerobic sports, such as running, sprinting and throwing. Modern overtraining has been titled parasympathetic overtraining and is seen in aerobic sports such as long distance running, swimming or cycling. The symptoms of modern overtraining are more wide spread and are mainly due to high volumes of high intensity training.
- Cardiopulmonary Parameters - Overtraining causes decreases in VO2max, maximum heart rate and maximum lactate concentration. Resting heart rate in the overtrained state has been reported to increase. There have some reports of changes in T-wave activity during electrocardiograms.
- Blood Chemical Parameters - While blood chemical changes have been found to be unreliable in identifying overtraining in certain sports, some success has been reported in its diagnosis of endurance trained athletes. Leukocycte, serrum ion, ferritin levels were shown to decrease with endurance overtraining. Other decreases in ammonia concentrations, serum glucose, free fatty acids, serum lipids have been shown.
- Neuroendocrine Parameters - Overtrained endurance athletes have demonstrated reduced cortisol, corticotrophic, growth hormone, endorphin, and prolactin levels. A 30 percent decrease in the testosterone to cortisol level has been recommended as an indicator of overtraining.
- Neurovegetative Parameters - In parasympathetic overtraining, a reduction in the evening urinary excretion of catecholamines. This is also in keeping with patients with decreased sympathetic response and may be due to an increased dopamine release from the hypothalamus. Increased dopamine levels lead to inhibition and can be responsible for emotional responses. In overtraining studies, the increased dopamine levels are based on increased plasma and brain tyrosine levels.
- Mood State - It has been suggested that depressive mood changes occurring closer to competition may indicate overtraining.
Diagnosis of Parasympathetic Overtraining
Symptoms of parasympathetic overtraining include reduction in performance, poor maximal performance, changes in mood states, decrease in maximum and sub maximum lactate levels, muscle soreness and stiffness and decreased heart rate at sub maximal and maximal levels.
Possible symptoms of parasympathetic overtraining include a 50 to 70 percent decrease in evening excretion of catecholamines, decrease in leukocytes, iron, haemoglobin and magnesium, decrease in free fatty acids, ammonium, very low density lipoproteins, increase in sub maximal noradrenaline plasma levels and a decrease in free testosterone.
The following are accumulated deductions based on findings in all 10 Research Reviews in this series:
- Heart rate monitoring appears to be a relatively effective method for identifying the early symptoms of overtraining. Overtraining can be recognized by an increase of six to 20 beats per minute in early morning resting heart rates or 25 beats per minute increases during sub maximal exercise.
- Glutamine is one of the most versatile amino acids found in the body. Its functions include transfer of nitrogen between organs, detoxification of ammonia, regulation of the body’s acid base balance, fuel for cells of the gut and the immune system and protein synthesis. Glutamine has a dramatic effect on skeletal muscle, kidneys and the immune system. While glutamine has a role in muscle building and recovery, it is also important for fighting infection. It has been reported that overtrained athletes appear to be more susceptible to infections. If this is the case, it could be associated with lowered levels of glutamine, which have a correlation with immune depression.
- A marker often recommended to recognise overtraining is muscle glycogen depletion. It appears possible that overtraining can occur without muscle glycogen depletion. Consequently, while reduced glycogen levels may contribute to fatigue it should be regarded as one of many factors associated with overtraining. In some studies, a reduced level of glycogen has been reported to cause reduced lactate levels at sub maximal workloads. Further examination reveals that glycogen levels did not deplete to the extent required of overtraining. Consequently, the decreased lactate levels at sub maximal levels were probably due to a reduced sympathetic drive.
- The greatest stimulus for overtraining is high intensity endurance training above the anaerobic threshold. Athletes performing this type of training often complain of heavy legs, increased perception of effort, chronic fatigue and sleep disorders. Researchers have reported between 31-84 features of overtraining. The 10 most prominent overtraining symptoms for the runner include heavy legs, sore muscles, high resting heart rate, poor motivation, sleep disturbances, low libido, frequent sickness or infection, weight loss, depression and higher perceived exertion.
- It is well reported that strenuous exercise can cause muscle damage. This is often reflected in an increase in myoglobin and creatine kinase in the blood. Marathon runners have presented with muscle damage, in the form of fibre necrosis and inflammation for the week following the race. The muscles continue to repair for the next week and then slowly regenerate for the next 10 to 12 weeks. It has even been shown that marathoners before the race have some muscle damage from the previous months training. This same response has also been reported in swimmers and rowers and exercising in an eccentric mode. One problem associated with muscle damage after exercise participation, is the perception by the exercise participant that the muscles are recovered, when in fact, they are still damaged. The condition can be compounded by additional workouts with extra stress taken up by the muscle, tendons, ligaments, joints and bones, which can then lead to overtraining.
- It has been reported that participation in moderately intense exercise can have a positive effect on fighting infections. It has been shown that there is an increase in the white blood cell count (leukocytes) after exercise participation. Different forms of exercise appear to stimulate different types of white blood cells. In long distance events, there is an increase in neutrophils, which eat the invading bacteria. In high intensity exercise, there is an increase in circulating lymphocytes (another type of white blood cell) which create antibodies to fight infection
- To effectively monitor overtraining, the client must be evaluated on an individual basis. Monitoring of the mood state combined with indices of fatigue and muscle soreness may successful in identifying clients who are “at risk” of overtraining. In the event of a client demonstrating the potential for overtraining a Profile of Mood States evaluation may provide an objective view for the client to consider.
- Blood hormone sampling has been recommended as a marker for overtraining. Some researchers have rated the monitoring of hormones or substrate more successful than performance criteria. Results of some hormones such as epinephrine and norepinephrine appear to be inconsistent in determining overtraining. The ratio of testosterone to cortisol has been recommended as a marker and has shown favourable results. This may be very specific to endurance overtraining, as some researchers have not found the same changes to occur in high intensity resistance training.
- Cortisol is one of the most abundant hormones in the body and is responsible for regulating metabolism. In overtraining it appears to decrease, which can reduce the effects of sodium, potassium and ATPase. Sodium and potassium are located across both sides of the cell membrane. To maintain the equilibrium of sodium and potassium across the membrane, the sodium potassium pump must be very active. With decreased levels of cortisol, as evidenced by overtraining, an increased concentration of potassium in the cell is noticed caused by the sodium potassium pump not functioning to its full capability. This may explain the muscle soreness and complaints often reported in overtraining.
- Two types of overtraining have been observed. Classical overtraining refers to sympathetic overtraining in anaerobic sports while modern overtraining is parasympathetic driven as seen in aerobic sports. Modern overtraining is more widespread and mainly due to a high volume of high intensity exercise.
- Recommendations for identifying overtraining include undertake an endurance test 14 days after the recovery period, monitor mood changes using a four point scale, monitor muscle soreness on a 4 point scale and measure basal catecholamine levels every seven to 14 days.