Science - Muscle Fatigue

HOW MUSCLES GET THE ENERGY THEY NEED TO WORK

1) Muscle needs energy to contract and as stated previously the ‘universal energy currency’ of living systems is ATP (adenosine triphosphate). This is largely produced within mitochondria, organelles which are often referred to as the ‘powerhouse’ of the cell. The ATP that results is used to provide the power for the muscle fibres to contract. Contraction itself (i.e. actual shortening movement) occurs when a bond is broken between ATP and one of its three phosphate bonds. It is the energy that is liberated by the breaking of this bond that causes the movement. Hence ATP is broken down to ADP (adenosine diphosphate). ADP is reconverted to ATP by donation of a phosphate from another high energy phosphate store in the muscle, creatine phosphate (CP). Mitochondria can burn glucose, fats and ketones to make carbon dioxide and water. Doing so ensures that a greater percentage of aerobic metabolism can be sustained, i.e. a subsequent slightly greater availability of oxygen and production of ATP. A diet rich in creatine has the potential to increase the availability of creatine phosphate, which can increase high energy phosphate supply during intense exercise. Mitochondria can burn glucose, fats and ketones to make carbon dioxide and water. They will do so give an adequate supply of oxygen.

2) Exposure to high altitude could theoretically improve an athlete’s capacity to exercise. Exposing the body to high altitude causes it to acclimatise to the lower level of oxygen available in the atmosphere. Many of the changes that occur with acclimatisation improve the delivery of oxygen to the muscles -the theory being that more oxygen will lead to better performance.

For any type of exercise lasting longer than a few minutes, the body must use oxygen to generate energy. Without it, muscles simply seize up and can become damaged. This type of exercise is called aerobic exercise, meaning with oxygen.

The body naturally produces a hormone called erythropoetin (EPO) which stimulates the production of red blood cells which carry oxygen to the muscles. Up to a point, the more blood cells you have, the more oxygen you can deliver to your muscles. There are also a number of other changes that happen during acclimatization which may help athletic performance, including an increase in the number of small blood vessels, an increase in buffering capacity (ability to manage the build up of waste acid) and changes in the microscopic structure and function of the muscles themselves.

WHAT IS MUSCLE FATIGUE AND WHAT CAUSES IT

Muscle fatigue, or physical fatigue, is the decline in ability of a muscle to generate force. It can be a result of vigorous exercise but abnormal fatigue may be caused by barriers to or interference with the different stages of muscle contraction. There are two main causes of muscle fatigue - limitations of nerve’s ability to generate a sustained signal and the reduced ability of calcium (Ca2+) to stimulate contraction.
THE PROCESSES THAT ALLOW A MUSCLE TO RECOVER AFTER EXERCISE

Well either lactate is oxidised back to pyruvate which can then enter the TCA cycle, or lactate is used as a substrate for gluconeogenesis in the liver, which produces glucose and releases it into the blood where it can then be taken up again by active muscles and along with the breakdown of intramuscular glycogen --> glucose, this glucose is then used to continue respiration (Cori Cycle)
Pyruvate is the end product of glycolysis/glucose breakdown (which occurs in the cell cytosol). If oxygen is present pyruvate is decarboxylated to Acetyl CoA and enters the Krebs cycle (also called TCA cycle), where some ATP is directly produced and the electron carriers NADH and FADH2 are generated for oxidative phosphorylation, the final step of aerobic respiration which produces high quantity of ATP for cellular functions. im assuming you've studied the krebs cycle? it usually comes up at gcse level

If oxygen isn't present in sufficient quantities (anaerobic respiration), pyruvate is reduced to lactate/lactic acid, this generates small amounts of ATP in itself for short term use in muscle cells. post-exercise, the lactate is either oxidised back to pyruvate, or is transported to the liver where it enters a pathway called gluconeogenesis, which produces glucose

Glycogen --> Glucose --> Pyruvate --(anaerobic)-->Lactate

And the reverse of the above happens after the exercise

THE EFFECTS ON ATHLETES OF SPENDING TIME AT HIGH ALTITUDES

Running at high altitudes decreases the amount of oxygen getting to the muscles. A low atmospheric pressure in the thin air makes the blood less oxygen-rich as it travels to the muscles. As the marathon proceeds and runners climb higher, the problem gets worse and worse as the runners' oxygen demands increase. Regardless of whether a runner lives and trains at a high altitude or not, high altitude slows performance.
The effects of high altitude on humans are considerable. The percentage saturation of hemoglobin with oxygen determines the content of oxygen in our blood. After the human body reaches around 2,100 m (7,000 feet) above sea level, the saturation of oxyhemoglobin begins to plummet.[1] However, the human body has both short-term and long-term adaptations to altitude that allow it to partially compensate for the lack of oxygen. Athletes use these adaptations to help their performance. There is a limit to the level of adaptation; mountaineers refer to the altitudes above 8,000 metres (26,000 ft) as the "death zone", where no human body can acclimatize.
REFERENCE LIST:

1)http://answers.yahoo.com/question/index?qid=20130516082623AAf5rb9

2)http://en.wikipedia.org/wiki/Muscle_fatigue

3)http://www.thestudentroom.co.uk/showthread.php?t=2394973

4)http://en.wikipedia.org/wiki/Effects_of_high_altitude_on_humans http://beta.active.com/running/Articles/The-Effects-of-High-Altitude-Training