Created by G.Baker 2017 Thesciencequeen.net

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1 Created by G.Baker 2017 Thesciencequeen.net

2 Skeletal muscles move the bones in the skeleton. When the muscles contract, it makes the joints able to move and lets us engage in physical activity of all kinds. Chemical energy is needed to cause muscles to contract. The chemical energy is a result of respiration.

3 Skeletal muscle is made of two different kinds of fibers: fast twitch (FT) and slow twitch (ST). On the average, we have about half ST fibers and half FT fibers. However, elite athletes have different amounts of ST and FT fibers. Depending on their sport they may have much more of one type than the other..

4 Fast twitch fibers use up energy very quickly. The muscle fibers contract very fast. They are used in activities that that short, but intense. Stop-and-go, change-ofpace movements in many team sports depend on FT fibers. Sprinting and other quick, forceful movements also use the fast twitch fibers

5 Slow twitch fibers do not get tired as quickly. They are used during prolonged, low to moderate intensity activities. Athletes with good endurance and aerobic capacities, like marathon runners and cross-country skiers have very high percentages of ST fibers.

6 Why do we get muscle fatigue? Lactic acid forms as a by-product of energy production by the muscles. Muscle fibers convert glycogen (which is formed from glucose) to adenosine triphosphate or ATP. ATP is the energy source muscle fibers use to make muscles contract. Some of the reactions in converting glycogen to ATP take place without oxygen, and when this happens a compound called pyruvate is produced. Some of this pyruvate can be converted into energy, but the excess becomes lactic acid.

7 Dark and white meat Chickens have fast and slow twitch muscle, too. Dark meat, like in chicken legs, is mainly made up of slow twitch fibers. White meat, like in chicken wings and breasts, is largely made up of fast twitch muscle fibers. Chickens use their legs for walking and standing, which they do most of the time. This doesn't use much energy. They use their wings for brief bursts of flight. This requires lots of energy and the muscles involved tire very quickly.

8 Purpose: Demonstrate how muscle fatigue works. Materials Clothespin/Test tube clamp Timer

9 Procedure: 1. Create a chart to show the data collected in this experiment. 2. Work with a partner. 3. Hold the test tube clamp in the hand that you use to write (your dominant hand). 4. Squeeze the clamp with your thumb and first two fingers until your fingers meet. 5. Relax your grip until the clamp is back in its original position. This is one squeeze. 6. Using the timer, your partner will record the number of squeezes you can do every 30 seconds for a total of 150 continuous seconds (5 trials). 7. Count the number of squeezes out loud. 8. At the end of the first 30 second period your partner will record the number of squeezes you made in your data chart. You continue to squeeze the clamp. Record the number of squeezes after 60, 90, 120, and 150 seconds. 9. Switch. Now your partner does steps Copy down your partner s data.

10 You Your Partner Muscle Fatigue Over Time 30s 60s 90s 120s 150s

11 When you were opening and closing the clothespin, your muscles were exercising anaerobically, drawing on their stores of glycogen to produce the ATP molecules that supply the energy they needed to contract. As the glycogen ran out, your muscles ran low on ATP and their ability to contract decreased. If you squeeze the clothespin slowly, you're exercising aerobically. In aerobic exercise, your muscles also draw on oxygen and the glucose and fatty acids carried in by the blood to produce ATP. Your ability to keep exercising aerobically depends on the delivery of oxygen and fuel molecules (glucose and fatty acids) to your muscles. And that depends on your circulation and respiration.

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