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Energy for Movement

09 Mar

Catatan Fisiologi Olahraga

BAB 1 : Energi Untuk Pergerakan

Anatomi : ilmu yang mempelajari tentang struktur atau morfologi organisme

Fisiologi : ilmu yang mempelajari tentang fungsi tubuh, dan bagaimana sistem organ, jaringan, dan sel bekerja dan berintegrasi untuk mengatur kondisi/lingkungan internal

Fisiologi Olahraga : Aplikasi konsep-konsep dari fisiologi latihan (exerccise physiology) untuk melatih dan meningkatkan performa olahraga atlet. Selain itu juga aplikasi informasi tersebut untuk desain dan evaluasi program pelatihan untuk mengurangi resiko overtraining.

Basic Energy System

Energi adalah kapasitas untuk melakukan kerja

Betuk-bentuk energi : kimia, mekanik, listrik, elektromagnetik, termal, nuklir

Energi dalam sistem biologi diukur sebagai kilokalori(kcal) : 1 kcal setara dengan jumlah energi panas yang dibutuhkan untuk mengaikkan suhu 1 kg air 1⁰C pada suhu 15⁰C.

Sumber Energi

Sumber energi dari makanan : karbohidrat, lemak, protein

ATP : Adenosine triphosphate , sebagai senyawa berenergi tinggi

  • Karbohidrat : ketergantungan tubuh kita terhadap karbohidrat selama latihan terkait dengan ketersediaan karbohidrat dan otot mengembangkan sistem yang baik untuk metabolismenya.tanpa suplai karbohidrat yang cukup, otot dan hati akan ‘kelaparan’ energi utamanya.
  • Lemak : Tubuh menyimpan banyak lemak dibandingkan karbohidrat, dan lemak mempunyai energi lebih tinggi dibandingkan karbohidrat dan protein, namun hanya asam lemak bebas yang digunakan untuk pembentukan ATP
  • Protein: protein dapat menyuplai 5-10% energi yang dibutuhkan untuk melanjutkan latihan.

Sel manusia membentuk ATP melalui tiga mekanisme, yaitu sistem ATP-PCr, Sistem Glikolisis, dan sistem Oksidatif.

1.     Sistem ATP-PCr (sori english mulai sini)

ATP and creatine phosphate (also called phosphocreatine or PCr for short) make up the ATP-PCr system. PCr is broken down releasing a phosphate and energy, which is then used to rebuild ATP. Recall, that ATP is rebuilt by adding a phosphate to ADP in a process called phosphorylation. The enzyme that controls the break down of PCr is called creatine kinase (5).

The ATP-PCr energy system can operate with or without oxygen but because it doesnt rely on the presence of oxygen it said to be anaerobic. During the first 5 seconds of exercise regardless of intensity, the ATP-PCr is relied on almost exclusively. ATP concentrations last only a few seconds with PCr buffering the drop in ATP for another 5-8 seconds or so. Combined, the ATP-PCr system can sustain all-out exercise for 3-15 seconds and it is during this time that the potential rate for power output is at its greatest (1).

If activity continues beyond this immediate period, the body must rely on another energy system to produce ATP

2.       Sistem Glikolisis

Glycolysis literally means the breakdown (lysis) of glucose and consists of a series of enzymatic reactions. Remember that the carbohydrates we eat supply the body with glucose, which can be stored as glycogen in the muscles or liver for later use.

The end product of glycolysis is pyruvic acid. Pyruvic acid can then be either funnelled through a process called the Krebs cycle (see the Oxidative System below) or converted into lactic acid. Traditionally, if the final product was lactic acid, the process was labelled anaerobic glycolysis and if the final product remained as pyruvate the process was labelled aerobic glycolysis.

However, oxygen availability only determines the fate of the end product and is not required for the actual process of glycolysis itself. In fact, oxygen availability has been shown to have little to do with which of the two end products, lactate or pyruvate is produced. Hence the terms aerobic meaning with oxygen and anaerobic meaning without oxygen become a bit misleading (5).

Alternative terms that are often used are fast glycolysis if the final product is lactic acid and slow glycolysis for the process that leads to pyruvate being funnelled through the Krebs cycle. As its name would suggest the fast glycolitic system can produce energy at a greater rate than slow glycolysis. However, because the end product of fast glycolysis is lactic acid, it can quickly accumulate and is thought to lead to muscular fatigue (1).

The contribution of the fast glycolytic system increases rapidly after the initial 10 seconds of exercise. This also coincides with a drop in maximal power output as the immediately available phosphogens, ATP and PCr, begin to run out. By about 30 seconds of sustained activity the majority of energy comes from fast glycolysis (2).

At 45 seconds of sustained activity there is a second decline in power output (the first decline being after about 10 seconds).

3.       Sistem Oksidatif

The oxidative system consists four processes to produce ATP:

  • Slow glycolysis (aerobic glycolysis)
  • Krebs cycle (citric acid cycle or tricarboxylic acid cycle)
  • Electron transport chain
  • Beta oxidation

Slow glycolysis is exactly the same series of reactions as fast glycolysis that metabolise glucose to form two ATPs. The difference, however, is that the end product pyruvic acid is converted into a substance called acetyl coenzyme A rather than lactic acid (5). Following glycolysis, further ATP can be produced by funnelling acetyl coenzyme A through the


Krebs Cycle
The Krebs cycle is a complex series of chemical reactions that continues the oxidization of glucose that was started during glycolysis. Acetyl coenzyme A enters the Krebs cycle and is broken down in to carbon dioxide and hydrogen allowing more two more ATPs to be formed. However, the hydrogen produced in the Krebs cycle plus the hydrogen produced during glycolysis, left unchecked would cause cells to become too acidic (2). So hydrogen combines with two enzymes called NAD and FAD and is transported to the


Electron Transport Chain
Hydrogen is carried to the electron transport chain, another series of chemical reactions, and here it combines with oxygen to form water thus preventing acidification. This chain, which requires the presence of oxygen, also results in 34 ATPs being formed (2).


Beta Oxidation
Unlike glycolysis, the Krebs cycle and electron transport chain can metabolise fat as well as carbohydrate to produce ATP. Lipolysis is the term used to describe the breakdown of fat (triglycerides) into the more basic units of glycerol and free fatty acids (2).

Before these free fatty acids can enter the Krebs cycle they must undergo a process of beta oxidation… a series of reactions to further reduce free fatty acids to acetyl coenzyme A and hydrogen. Acetyl coenzyme A can now enter the Krebs cycle and from this point on, fat metabolism follows the same path as carbohydrate metabolism (5).


Fat Metabolism

So to recap, the oxidative system can produce ATP through either fat (fatty acids) or carbohydrate (glucose). The key difference is that complete combustion of a fatty acid molecule produces significantly more acetyl coenzyme A and hydrogen (and hence ATP) compared to a glucose molecule. However, because fatty acids consist of more carbon atoms than glucose, they require more oxygen for their combustion (2).

So if your body is to use fat for fuel it must have sufficient oxygen supply to meet the demands of exercise. If exercise is intense and the cardiovascular system is unable to supply cells with oxygen quickly enough, carbohydrate must be used to produce ATP. Put another way, if you run out of carbohydrate stores (as in long duration events), exercise intensity must reduce as the body switches to fat as its primary source of fuel.


Protein Metabolism
Protein is thought to make only a small contribution (usually no more 5%) to energy production and is often overlooked. However, amino acids, the building blocks of protein, can be either converted into glucose or into other intermediates used by the Krebs cycle such as acetyl coenzyme A. Protein may make a more significant contribution during very prolonged activity, perhaps as much as 18% of total energy requirements (1).

The oxidative system as a whole is used primarily during rest and low-intensity exercise. At the start of exercise it takes about 90 seconds for the oxidative system to produce its maximal power output and training can help to make this transition earlier (1).

Beyond this point the Krebs cycle supplies the majority of energy requirements but slow glycolysis still makes a significant contribution. In fact, slow glycolysis is an important metabolic pathway even during events lasting several hours or more

Sumber : Kuliah Fisiologi Olahraga, http://www.sport-fitness-advisor.com/energysystems.html

 
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Posted by on March 9, 2011 in Fisiologi Olahraga

 

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