Part I: Isometric and Isotonic Contraction in Muscles

Investigating Muscles Lab

Background information: Most of the systems of the body play some part in achieving movement, but it is the skeletal and muscular systems acting together that actually produce movements. The architectural plan of the skeleton has been investigated and an understanding of how joint structures make movements possible has been made clear. Bones and joints can only move, however, in association with muscle tissue. Muscle tissue promotes movement because of its contractility, extensibility, and elasticity. A resting muscle has potential energy that is converted into kinetic energy when the muscle contracts.

Part I: Isometric and Isotonic Contraction in Muscles. Materials: The book: “Modern Human Physiology” (old burgundy books). Measuring tape Procedure:

A. Consult the diagram on page 113 of the textbook (figure 7-2) and observe the location of the origins and insertion of the biceps brachii. Sit relaxed in a chair and place the fingers of each hand under each side of the seat. Measure with a tape measure, in centimeters, the length of the biceps when relaxed. (Record) Now try to lift up the chair with your fingers while seated. While the muscle is working, have your partner measure its length, and observe and feel the muscle. (Record) B. Sit relaxed with one arm resting on a table. Have your partner measure with a tape measure, in centimeters, the length of the biceps muscle and record. On the palm of your hand, place an object that you lift by flexing the forearm. Raise the object and again measure the length of the biceps. Observe and feel the muscles of the upper arm while the arm is raised. (Record) Data: A. Muscle length relaxed: ______cm Muscle length contracted: ______cm Describe how the muscle felt. B. Muscle length relaxed: ______cm Muscle length contracted: ______cm Describe how the muscle felt. Questions: 1. Define isometric. 2. Define isotonic. 3. Even though your hands did not lift the chair, what did you observe about the length and tension of the biceps? 4. Part A is an example of what kind of contraction? 5. In Part B, your arm lifted the weight. What did you observe about the length of your biceps and the size of the upper arm this time? 6. Part B is an example of what type of contraction?

Part II: Muscle Action Procedure: 1. Place your fingers along the angle of your jaw just in front of your ear. Grit your teeth and RECORD what happens to the hardness of the muscle is your cheek. 2. With the thumb and little finger of one hand, span the opposites arm’s bicep from the just below the elbow to as close to the shoulder as possible. Bend the arm and RECORD the change in the length of the muscle. 3. Measure the circumference of your bicep, RECORD. Flex your bicep muscle, measure, and record the new circumference. Find the difference and RECORD. Data: 1. The muscle felt ______. 2. The distance between my fingers ______. 3. Centimeters Muscle relaxed Muscle contracted Difference between

Part III: Effect of Temperature on Muscle Action Materials: Dishpan of ice water and timer Procedure: 1. Count the number of times you can make a fist in 20 seconds. Start with your hand completely outstretched and make a tight fist each time as rapidly as you can. RECORD 2. Submerge you hand in a dishpan of ice water for one full minute. 3. Remove your hand and immediately count how many forceful fists you can make in 20 seconds. RECORD Data: Temperature Number of fists Normal Ice water Questions: 1. What effect did the cold temperature have on the action of your hand muscles? Explain.

Part IV: Muscle Fatigue Background information: Just as an automobile must be supplied with gasoline as a source of energy before it can move, your muscles also require energy in order to contract. This energy, in the form of ATP, can be produced with oxygen (aerobic respiration) or without oxygen (anaerobic respiration). In animal cells anaerobic process is called Lactic Acid Fermentation, and it occurs when there isn’t oxygen available in the cells for aerobic respiration. An accumulation of lactic acid can cause fatigue in a muscle. Fatigue is when a muscle loses its ability to contract. This can also be caused by an interruption in the muscles blood supply or a lack of acetylcholine in the motor neurons. Materials: Clothespin or rubber ball, timer Procedure: 1. Count how many times you can tightly squeeze a rubber ball in your hand (or open and close a clothespin with your thumb and index finger while the other fingers are held out straight) in 20 seconds. RECORD 2. Repeat the squeezing (or opening closing) 9 more times, for a total of 10 trials. DO NOT REST BETWEEN TRIALS!! RECORD Data: 10 Trials Rubber Ball or Obtain graph paper and make a line graph of Clothespin your results. Be sure to fill in the values on 1 the vertical (# of squeezes) and horizontal 2 (Attempts number) axis and title the graph. 3 4 Question: 5 6 1. What effect did fatigue have on the action 7 of your hand muscles? Explain. 8 2. Your muscles would probably recover enough 9 after 10 minutes to operate at the original efficiency. Explain why?