Fatigue

That inability to continue exercise at a given intensity due to physiological, biomechanical and/or psychological demands

Local fatigue - involves fatigue in specific muscles due to exercise. *Experienced in quadriceps after mogul skiing and/or triceps after performing maximum dips fitness test

General Fatigue - fatigue relating to the entire body after a specific exercise session (can be physiological and psychological). *Experienced after a full weights session, completing a marathon (42.2km) and/or 36 holes of golf.

The type of activity being performed – Intermittent as opposed to continuous activity. Intermittent activity allows for periods of rest and therefore fatigue is often delayed.

The type of muscle fibre involved – slow or fast twitch fibres. Slow twitch fibres are more fatigue resistant than fast twitch fibres.

The type of muscular contraction being performed isotonic, isometric or isokinetic

• Central Fatigue - is an exercise in juiced inability to fully activate a muscle. The precise cause of central fatigue is not known. It is believed to be associated with changes within the brain that reduce neural drive and muscle fibre activation. Central fatigue is thought to exist as a protective mechanism to prevent irreparable muscle damage.

Referred to the depletion of energy fuels or substrates that serve to power muscular contractions. They include adenosine triphosphate (ATP), creatine phosphate (CP) and glycogen.

• during very high intensity, short duration anaerobic type activities, muscular stores of ATP are used within the first few seconds of activity (5-10m of sprint)

• once the stores have been depleted the muscles then used creatine phosphate stores as fuel to provide energy to reply niche ATP from ADP and Pi

• however, for phosphocreatine (PC) stores also

Is the term used in endurance sports, particularly running, to describe the condition caused by the depletion of glycogen stores in the muscles and liver, which manifests itself as precipitous fatigue and loss of energy. The condition can be avoided by ensuring that glycogen levels are high when the exercise begins, by maintaining glycogen levels during exercise by eating and drinking Carbohydrate-

A substance produced as a result of chemical reactions within the associated with the production of energy for ATP resynthesis. Metabolic by-products include adenosine diphosphate (ADP), inorganic phosphates (Pi), lactic acid and hydrogen ions.

•Lactic acid accumulates in the muscles only after relatively short duration, high intensity exercise.

• lactic acid levels of endurance athletes, such as marathon runners and triathletes, at the completion of their events aren't much higher than resting levels, despite the obvious fatigue.

• lactic acid within the muscle quickly dissociates (splits) into lactate and hydrogen ions (H+).

•The accumulation of hydrogen ions in the muscle cells (stemming from the dissociation from the lactic acid as a result of anaerobic glycolysis during high intensity activity) results in an increase in acidity within the muscle (otherwise known as muscle acidosis).

• The increased acidity results in an decrease in the muscle P Hache from the normal value of around 7.1 at rest to 6.4 at exhaustion, a value

• Inhibition of excitation-contraction coupling by hydrogen ions - A decreased pH has been demonstrated to affect the binding of the actin and myosin muscle filaments, by reducing the affinity of troponin for calcium (Ca2). Although the mechanism is not clear, hydrogen ions (H+) may compete with calcium for the troponin-binding site. This appears to affect type II fibres more than type I.

Is the term used to describe the physiological process of converting an electrical stimulus to a mechanical response. In terms of muscle physiology, it is the nerve impulse that leads to a muscle contraction. Potassium (K+) is also implicated in this process.

* potassium is one of several substances that move into and out of the intracellular and intercellular spaces if the muscle during

Central fatigue mechanisms are the 'result in any force of decline caused by reduction in the firing frequency of the motor neurons involved'.

There are several central fatigue mechanisms may operate including:

• Fatigue at the neuromuscular junction

•Central nervous system fatigue

The thermoregulatory mechanisms of fatigue occur as a result of changes in the body is called temperature, practically increase cool temperature, which can lead to hyperthermia and dehydration.

• The Thermoregulatory model proposes that the onset of fatigue will occur as temperature reaches a critical level of around 40°C. This is due to a failure of the central nervous system (CNS) to supply a constant drive for muscle contraction to occur at this temperature.

• during prolonged exercise, the increased frequency of muscular contraction and extended time period of energy metabolism result in the

• usually on high body temperature: elevated core temperature

• The onset of hypothermia under these conditions has been linked to reduce blood flow to the brain, limiting the supply of fuels (glucose) and the removal of waste products

• fatigue associated with hypothermia places additional stress over and above that imposed by exercise on a body systems. Under these

• dehydration is a deficiency in the body's fluid stores occurring when fluid loss exceeds fluid intake

There are three main types of dehydration:

1. Hypertonic, which is primarily a loss of water

2. Hypotonic, which is probably a loss of electrolytes, in particular sodium

3. Isotonic, which is an equal loss of water and electrolytes.

Dehydration symptoms initially consist of the sensation of thirst and discomfort, possibly along with loss of appetite and dry skin. Symptoms of mild dehydration include thirst, decreased urine output, abnormally dark urine, headache, dry mouth and dizziness. In moderate to severe dehydration, there may be no urine output at all. Other symptoms include lethargy, fainting and seizures, and death may occur.

A thermal risk associated with exercising in cold environmental conditions, and it can lead to the development of fatigue-like symptoms and subsequent decline in the ability to physically perform. When hypothermia first develops (mild), the body initially directs its attention to reducing sweat loss and generating heat through shivering and other physiological responses. If body temperature continues to fall

Describes the balance betweenlactate entry into and removal from the body – it is the point beyond which agiven exercise intensity or power output cannot be maintained by an athlete.

LT1:

A rise in blood lactate concentration above baseline values and will normally occur around a blood lactate concentration of 2 mM. This value will vary between individuals of different aerobic fitness. It is referred to as LT1 but is also known as the ‘aerobic threshold’.

LT1 represents the exercise intensity

Chronic Fatigue - Extreme tiredness related to the depression of the bodies immune system (can be physiological or psychological) *Experienced as chronic fatigue syndrome, overtraining syndrome, recurrent minor illness, viral infections and/or insomnia

contraction.

- The fitness level of the performer

- The mental state of the athlete

- Hydration levels

- Duration of activity

- Intensity of activity

- Food Fuel storage levels

Peripheral fatigue - originates in the muscle and result in a reduction in muscle power during exercise. This type of fatigue can occur for a number of reasons, including fuel depletion or the accumulation of metabolic by-products (ADP, Pi, and lactic acid), as well as a loss of muscle-fibre activation resulting from changes in sodium (Na+), potassium (K+) and calcium (Ca2+) ion concentrations.

rich substances, or by reducing exercise intensity.

that appears to be incompatible with the normal muscle cell function.

•Changes in pH of this magnitude adversely affect energy production and muscle contraction, resulting in muscular fatigue.

Effects of hydrogen ions on Crossbridge cycling - increased hydrogen ion accumulation also decreases myosin ATPase activity which slows ADP release, and subsequently the overall rates of Crossbridge cycling. Again, this tends to affect type II muscle fibres more than type I.

glycolysis

Inhibition of glycolytic enzymes - decreased pH levels within muscles (increased acidity) appears to be associated with a decrease in the action of the enzymes associated with anaerobic

muscular contraction potassium influences excitability of the muscle membrane during muscle contraction potassium moves out of the muscle cells into this into the intercellular space. Building up in the t-tuble system and the muscle fibre in general. This makes it more difficult to excite the muscle and therefore muscle contractions are inhibited or reduced. This occurs most

notably during high intensity exercise and appears to be some sort of safety mechanism content preventing muscle damage.* The t-tuble system is a network of tiny tubes in muscle fibres that allow electric signals, set up on the muscle fibres surface (muscle membrane) in response to Nova signals, to move deep inside the muscle and excite muscle fibre.

production of excess heat. Combining this with a hot and humid environment and athletes body temperature will rise above baseline levels quite rapidly.

• Hot and/or human conditions limit cooling, as the temperature and water vapour gradients between the skin and air do not allow for optimal heat dissipation (loss). Under these

conditions, body temperature becomes a factor limiting performance of high intensity in endurance events.

conditions increased demands placed on the cardiovascular system to maintain core temperature with the normal range Via redirecting bloodflow to the skin and increasing sweat rates• this increased surface bloodflow reduces the amount of bloodflow to the working muscles (redirection of blood flow) relative to the amount that would normally be directed to the muscles when exercising under cooler conditions

• The decreased bloodflow to the working muscles results in a reduction in the oxygen supply to them, and this in turn increases the bodies

resilience on the anaerobic pathways for the supply of energy. This results in an increase in accumulation of anaerobic by-products (such as hydrogen ions) that are associated with anaerobic metabolism. These by-products as we have seen previously are implicated as causes of muscular fatigue

• at the same time it appears that central fatigue mechanisms (mainly perturbation of the brains ability to sustain sufficient activation of the skeletal muscles) are also implicated as core and brain temperatures rise.

• research studies suggest that the central nervous system aspect of

hypothermia-induced fatigue each appears to be more relevant during prolonged moderate intensity exercise, where the temperatures of the core and brain may exceed 40°C, where as the impairment in oxygen delivery to exercising muscles is more relevant during high intensity exercise, with a reduced performance level (fatigue) is highly associate with the reduced muscle bloodflow and the consequential decrease in oxygen delivery to the exercising muscles.

* of these, isotonic dehydration is by far the most common• as core body temperature rises, for example, during exercise (particularly when performed in warm or hot and/or humid conditions), the increased rate of sweating may result in a reduction in the blood plasma volume, especially if sufficient replacement fluids are not consumed.The decrease in blood plasma volume leads to a reduction in the amount of blood available to working muscles as well as for blood flow to the skin surface for dissipating heat. The metabolic consequences of reduced blood flow to the working muscles are a factor in the fatigue experienced when

exercising in a dehydrated state. Furthermore, the decreased blood flow to the skin also results in a reduction in the body's ability to cool itself via evaporation of sweat from the skin. As a result, core body temperature may continue to increase, with the potentially catastrophic consequence of heat stroke.A reduction in body mass(weight) of only 2 to 3 per cent, which would be nearly impossible to detect,can drastically reduce physical performance. This is a major source of fatigue in sports that require athletes to perform for prolonged periods in hot and humid conditions, such as motor racing.

Factors being:

- The duration of the training session or competition

- The particular environmental conditions such as the air temperature, humidity levels and even the playing surface

- The athlete's acclimatisation to conditions.

the body begins to shut down both physically and mentally. The ability to perform coordinated movements is severely compromised, and many people who develop moderate hypothermia appear to be extremely lethargic. This has much to do with the greatly decreased blood flow to the extremities as blood is redirected to the major organs to sustain their function.In severe hypothermia the person maybe comatose and death usually occurs if the core body temperature falls below 28°C.

that coincides with a shift in fuel metabolism from predominantly fat to carbohydrate. Coaches commonly use this point to determine the highest speed or power output an athlete can sustain during longer ultra-endurance events (for example, the Hawaii Ironman competition). This enables athletes to maximise fat use and spare carbohydrate stores thereby enhancing performance. It is also used to monitor training effectiveness as LT1 will occur at higher exercise intensities with improved aerobic fitness.

LT2:The second transition point, is an inflection in blood lactate

concentration that exponentially rises thereafter with increasing exercise intensity. Generally accepted that LT2 values will occur around a blood lactate concentration of 4 mM; however, this value, like LT1, will vary between individuals according to their aerobic fitness level.The intensity that coincides with LT2 signals a marked increase in the rate of carbohydrate metabolism to meet the new ATP demands. LT2 represents the highest steady state exercise intensity (that is, lactate production = lactate removal) an individual can perform for a longer duration(30 minutes to 2 hours).By definition, LT2 will vary greatly with the aerobic

fitness level of an individual and therefore change with the type of training performed. It is this second transition point, LT2, which is most relevant to performance in moderate- to high-intensity running events such as 5 and 10 kilometre races. It is also an important predictor of performance for world-class marathon runners, who will maintain this intensity throughout their race.

Lactate Inflection Point, the rise in H ions has occurred and they will start to accumulate to the point of interfering with muscle contraction.Lactate is used to tell us about Hydrogen. LIP will occur later if the person is aerobically trained.The better trained athletes don’t produce as much lactate and H⁺ ions, because they have trained their aerobic energy system better and the cardiovascular system works more efficiently for O2 uptake and use in the resynthesis of ATP.

deplete rapidly after about 10 seconds of all out effort, the muscle stores of creating phosphate are virtually full exhausted. If the activity is to continue, the body must change its predominant supply of energy for ATP resynthesis from the creatine phosphate system to the anaerobic glycolysis energy system. During longer continuous activities energy for ATP resynthesis is derived predominantly from the aerobic metabolism of carbohydrates in the form of glycogen. Stores of glycogen in the muscle and liver computer continues exercise periods of 90-180 minutes. muscle glycogen is generally utilise first, then as the stores are depleted,

the body utilises liver glycogen stores. As total glycogen stores become depleted the body moves to relying predominantly on fats as a source of energy for ATP resynthesis.• However, breakdown of fats to release energy is less efficient than the breakdown of glycogen – it requires more oxygen to metabolise fat than it does glycogen. Often resulting in a decrease in exercise intensity owing to the additional amount of oxygen required to produce energy for ATP resynthesis breakdown of fats. This phenomenon is referred to in athletics circles as "hitting the wall".