Fatigue - affects on the body

GCSE Physical Education (Sport & Coaching)

Matt Brown ND2B

Task 4

Fatigue

The body uses food as energy as we have discussed in task 3 but when the body is low on what it needs it becomes fatigued. Often the thing the body is low on is oxygen, this is a major factor in fatigue.

(Wilmore and Costill, 1988) described Fatigue as a general sensation of tiredness as well as a decrease in muscular performance. Muscular fatigue occurs in athletes after a tough training session. This description is very general and does not explain what causes fatigue.

(Answers.com, 2005) believe fatigue is the decreased capacity or complete inability of an organism to function normally because off excessive stimulation. This description is better then the first as it states that excessive stimulation, even lack of sleep, will cause the body to fatigue. It is the body’s way of saying it needs rest.

(Gandevia et al., 1995; Hagberg, 1981; Hawley et al., 1997) describes fatigue as the inability to continue functioning at the level of one's normal abilities. This is also very general but it is clear in what it describes.

performance may decrease for a number of reasons:(can performance improve)

accumulation of waste products lactic acid
depletion of energy stores glycogen
changes in physio chemical state of the muscle electrolytes
disturbances in the processes of muscular co-ordinbation-CNS

Neuromuscular fatigue - neural fatigue and muscular fatigue

CNS has 2 basic processes:

Excitation of the necessary muscle fibers
Inhibition of nueral firing

Fatigue can be caused due to the inability of the CNS to activate the required muscle fibres. This occurs when the impulse doesn’t get to muscles so they don’t contract. this is because of the reduction in the release or synethesis of ACH (acetylcholine). ACH is responsible for helping the impulse jump from the nerve to the muscles (synaptic cleft).

Reasons for muscle fatigue are due to the impulse not being able to jump from the nerves to the muscles. This could occur from:

There is an increase in the amount of cholinesterase (which is responsible for destroying ACH) this means that impulse can not reach the muscle because there is nothing to help it.

There is a decrease in the amount of cholinesterase, this results in a build up of ACH. Then overloaded-muscle fibres develop a higher threshold for the ACH so the body does not produce it when it needs just a little bit. This occurs in people who do a lot of exercise like athletes. If you are an athlete your body is used to getting the ACH. the muscle gets used to having all this ACH so it doesn’t contract and needs more to fire up.

Fatigue during exercise may also be due to, less calcuim being avaliable for muscle contraction.

Result of neuromuscular fatigue is that there is a decresae in the rate at which motor units activate muscle contraction.

The effects of metabolic bi-products (lactate/carbon dioxide etc)

(Meyerhof, 1920; Hill, 1932) state it has been known that isolated muscles made to contract until fatigue accumulates lactic acid. Further, it was observed that if oxygen was present in recovery, lactic acid level declined while glycogen concentration and contractile function were restored.

The system that creates the most fatigue is the lactic acid system. This uses glucose as an energy source, this gets broken down into pyruvic acid (which gets turned into lactic acid) and hydrogen. The lactate and hydrogen ions in the muscle affect muscle contraction and cause fatigue. It does this by interfering with the connection between actin and myosin, changes in acid base status and ca2+ ion function. Pyruvic acid can also be converted into acetyl coa. It depends if oxygen is present or not to what it gets turned into to. No oxygen presents means lactic acid, oxygen present means acetyl coa.

(Brain Mac) states the conversion of glucose to pyruvic acid leaves a hydrogen ion which gets picked up by nicotinamide adenine dinucleotide (NAD), this becomes NADH. This drops the hydrogen off at the mitochondria to be combined with water. If there is insufficient oxygen then NADH cannot release the H+ and they build up in the cell. To prevent the rise in acidity pyruvic acid accepts H+ forming lactic acid which then dissociates into lactate and H+. Some of the lactate diffuses into the blood stream and takes some H+ with it as a way of reducing the H+ ...

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It is not lactic acid that causes symptoms of fatigue, it is the build up of hydrogen ions. Hemoglobin acts as buffer and takes away hydrogen ions making blood less acidic in aerobic exercise but in anaerobic intensity the number of hydrogen ions is to high and it cant take it all away so it builds up. This causes a decrease in ph, this high acidity inhibits the action of enzymes such as phosphofructokinase (PHK) enzyme. Therefore energy can no longer be released from glycogen.

Hydrogen can displace calcuim which alters muscle contraction. If there is not calcuim present then the actin and myosion can not combine. A build up of lactic acid causes a build up of calcuim and calcuim ions fail to be released for muscle contraction. The absence of calcuim means that that the sliding filament theory cannot take place. During contraction calcuim ions bind to tropinin, causing exposure of the vross-bridge, allowing actin and myosin to attach.

While lactic acid may play a role in fatigue its supposed role in muscle soreness has been disproved and it is now being recognized as more of a positive player in metabolism. George A. Brooks has described lactic acid as a key substance used to provide energy, dispose of dietary carbohydrate, produce blood glucose and liver glycogen, and promote survival in stressful situations.

Survivals in stressful situations occur when there is not enough time to get oxygen into the muscles and the immediate source if ATP has been used. You can not just stop working so the body cleverly converts glycogen into ATP without oxygen.

When oxygen does reach the muscles quickly enough the production of lactic acid stops. Even more impressively the lactic acid that has accumulated now gets used up, it either gets converted back to glycogen by the liver or utilized for energy.

Lactic acid is continuously being formed and removed from the body, even at rest. Studies show that during aerobic glycolysis lactate production seems to increase in proportion to our metabolic rate. At some point, depending on exercise duration and intensity, a workload will be reached in which lactate concentration is greatly magnified. This is known as the lactate threshold and can usually be elicited between 50-80 percent of a person's maximal oxygen consumption, VO2max. It is at this point in which the rate of lactic acid appearance becomes greater than the rate of disappearance. This occurs in events like 400m. Most athletes train at there lactate threshold as it shift there threshold higher, this normally occurs after 6-8 weeks of training.

Lactic acid can be positive when used effectively. It can cause problems with the acidity level of the blood, when acidity increases contractile and metabolic functions are hindered.

Energy comes from anaerobic glycolysis which increases carbon dioxide in the system, used because it can’t get all the oxygen it needs.

This means an increase in carbon dioxide in blood which stimulates chemoreceptor’s to increase ventilation-OBLA-onset of blood lactate accumulation

The hydrogen carbonate ion produced by the kidneys; this absorbs hydrogen ions from the lactic acid and forms carbonic acid, which in turn degrades to form Carbon dioxide and water, both of which are eliminated via the lungs.

Oxygen debt and excess post-exercise oxygen consumption (EPOC)

(Wilmore and Costill, 1988) states oxygen consumption is a measure of a person’s ability to take in and use oxygen. During low intensity exercise with a constant power output, oxygen uptake increases for the first few minutes, until the oxygen demand by the body is met by the oxygen consumption. At the start of exercise the body uses energy through anaerobic systems until the aerobic system kicks in. It kicks in when the body gets used to the new demand put upon it. The body supplies energy without oxygen at first so the body owes the oxygen this is called oxygen deficit. This oxygen that is owed is paid back after exercise when the body recovers. It does this by keeping oxygen consumption higher then it normally would at rest, this is called oxygen debt.

Fig.1 this shows a graph of oxygen consumption during exercise (digital humans)

The aerobic system is the most efficient system in terms of ATP production at a steady rate. The aerobic system cannot be used immediately in exercise this is because:

It takes time for the cardiovascular system to get oxygen to the muscles
The aerobic system is kick started by the build up of excess ADP in mitochondria
The rate of demand for ATP is simply too great to be met by the aerobic means

Oxygen deficit can be calculated as the difference between the amount of oxygen that is required and the amount that is actually consumed.

EPOC is the oxygen uptake above resting values used to restore the body to pre exercise state. As the contribution of anaerobic mechanisms supporting the exercise increases, the exercise duration decreases. This simply put is the harder you work the less amount of time you will be able to work for.

This is the recovery period after cardiovascular exercise where there is elevated oxygen consumption. It can be described as the amount of oxygen consumed during recovery in excess of that which would have ordinarily been consumed at rest. Some factors that contribute to EPOC include the replenishment of PC and ATP, the conversion of lactate to pyruvate, and the resynthesis of glycogen. In addition, during this recovery period the increased oxygen demand is needed to help the body in adjusting the increased body temperature, heart rate and ventilation to a resting level, as well as the reoxygenation of hemoglobin (in the blood).

(Hill and Lupton) theorized that the body needs to replace the oxygen used by working muscles during mild to intense bouts of exercise. More recently, researchers have used the term EPOC to describe the several different events that occur as the body restores itself to homeostasis, or rest. These are what occur during EPOC:

Replace ATP
Remove lactic acid
Replenish myoglobin with oxygen
Replacing lost glycogen stores
Temperature recovery
Creatine phosphate replenishment

There are two phases to EPOC fast and slow recovery.

Fast recovery is a non lactate component (alactacid). Used to replenish stores of ATP-PC and resupply myoglobin with oxygen. This occurs quickly and is the steep part of oxygen debt in Fig.1. it only take around 2-3 minutes in which time 2-3 litres of oxygen above resting amount has been consumed. After the three minutes the body should be recovered to repeat the exercise.

Slow lactate recovery is a lactate component (lactacid). This involves the replenishment of muscle glycogen and as well as the oxidation of lactic acid. This lasts a lot longer and is the flatter part of Fig.1 at the end. The lactic acid is removed into the blood or oxidized in the mitochondria. This recovers quicker doing light aerobic work, a light jog involved in a cool down will help.

Lactic Acid is also converted into muscle and liver glycogen, glucose and protein and some is excreted from the body as sweat or urine. The process of lactic acid removal takes approximately 1 hour, this is faster if a cool down is completed. 80% of lactic acid is turned to glycogen, the other 20% is turned into oxygen, carbon dioxide and water.

Training and its effects on fatigue.

Energy store fatigue

High intensity exercise-ATP and Pc become depleted.
Muscle fibers most frequently recruited become individually depleted of glycogen-Reduces number of fibres avaliable

Association between fatigue and lactic acid has been recognised since the 30,s
Lactic acid is partly responsible for fatigue in short term high intensity exercise.
Sprinting cycling swimming all result in a large accumulation of lactate- anaerobic glycolysis
65% of lactic acuid is converted to carbon dioxide and water, 20% into glycogen,10% into protein and 5% into glucose

the elevation of lactic acid within the blood and muscle negatively affects both meduim and long term exercise (Karlson 1971). This only occurs when there is a build up of lactic acid and with training tis can occur much later.

Stafford brown et al (2003) states training has the effect of increasing the bodys ability to exercise for longer without tiring. The training must be specific to the sport the athlete is competing in. A sprinter must train anaerobically in order to increase their tolerance to lactic acid and increase PC stores. If a marathon runner did the same training it would not be beneficial to their sport.

During intense training, the levels of lactic acid in most racers range from 12 μL/kg to as much as 20 μL/kg; lance Armstrong doesn't go above 6 μL/kg. The result is that less accumulates in Armstrong's system.

Training and recovery of ATP PC system

To work the ATP-PC system to its full potential the movement you use to train must be specific to you sport. Training this system is very intense and involves working at maximal levels. Work per rep must not exceed 10 seconds other wise this starts to train the lactic acid system. Work rest ratio should be 1:3 this means for every 1 minute of work you should get 3 minutes rest.

A set of exercises should not exceed more then 1 minute so 6 x 10 second reps in set. After each set there should be about 3-10 minute rest to allow the energy system to recover properly. The Energy systems can be trained every other day as they recover quickly. A training program for the energy systems should last 8-12 weeks.

To develop this energy system, sessions of four to seven seconds of high-intensity work at near peak speed are required. For example, a training session might consist of:

60 m runs performed 15 times with a 60 second recovery period
20 m shuttle runs repeated 20 times with 45 seconds recovery.

By following this type of training, the body will produce more enzymes that make ATP via the PCr energy system and may even be able to store more PCr in the muscles.

Those link to specificity, the body:

Stores of ATP increase
Stores of pc increased
Increase in amount of anaerobic enzyme-creatine kinase
Overall leads to the maximum peak power output of a muscle

Lactic acid system/anaerobic glycolysis

This energy system requires no oxygen but as a side effect produces lactic acid.

This system uses the break down of muscle glycogen as energy. This system lasts between 10 seconds and 2 minutes peak power occurs around 30 seconds.

This system is trained using interval training the intensity of the exercises should be maximal or near maximal. The work to rest ratio is 1:2 so if you run for one minute you should rest for 2 minutes. The total volume of work should not exceed 10-12 minutes per set. The rest between sets should be between 10-15 minutes long.

Light aerobic work, speeds the recovery and removes lactic acid. Training can be done every other day the training program should last 8-12 weeks.

Example sessions that will help to train this energy system are:

150 m intervals with 20 seconds recovery until pace significantly slows.
300 m repeated eight times with three minutes recovery.

By performing this training, the body will be able to withstand higher levels of lactic acid and produce more enzymes that will help in the production of ATP via the lactic acid system.

Exercises of over 60 seconds, can overload the lactic acid system. This system adapts by:

Glycogen stores within muscles increased, due to increase in size or number of mitochodria.
Cells learn to use and store more rapidly
Increase in glycotic enzymes
Increase in lactate dehydrogenase aids convertion of pyruvic acid
Buffering capacity of muscle against lactic acid increased
Can work longer before hydrogen inhibits enzyme action

Aerobic system

This system requires oxygen and most adaptations from exercise occur in this system. There is no lactic acid and can even burn lactic acid as fuel. The main sources of fuels are complex carbohydrates and fats as fuels.

When training this system you should Increase duration of the exercise then increase the intensity. This allows both the capacity to use and deliver oxygen to improve.

Total work volume should be between 15-60 minutes for both continuous and interval training. Continuous training works best between 30-60 minutes. Interval training a rep may be between 10secs up to 7 minutes Work rest ratio is 2:1 so for 10 minutes work get 5 minutes rest.

Training should occur at least every other 6 days and at most every second day. The training program should last between 3-6 weeks.

Bibliography