Unit III Muscle Lab

How Do Your Muscles Work?

INTRODUCTION:

Much of the work of the body depends on the contraction of skeletal

muscles. In this experiment you will first observe the characteristics of

muscle contraction and then will investigate the effects of two factors -

temperature and fatigue - on the action of your muscles.

MATERIALS:

dishpan of water

narrow strip of paper which will fit around upper arm

ice or snow

rubber ball or clothespin

timer (clock, watch, or stop watch)

PROCEDURE:

The following exercises will help you understand what happens to your

muscles when they contract.

Muscle Action

1. Place your fingers along the angle of your jaw just in front of your

ear. Grit your teeth and observe what happens to the hardness of the

muscles in your cheek.

The muscle goes from flaccid to hard as you grit your teeth.

2. With the thumb and little finger of one hand, span the opposite arm's

biceps (front muscle of the upper arm) from the elbow to as close to the

shoulder as possible. Bend the arm and observe the change in the length of

the muscle.

From extension to flexion the bicep shortens.

3. Wrap a strip of paper around your upper arm and mark the circumference

of your arm on the paper. Clench your fist tightly and mark the new

circumference on the paper. Observe what happens to the circumference of

the muscle.

The circumference increases as the bicep and tricep both try to contract.

Effect of Temperature on Muscle Action

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. Do it

as rapidly as you can. Record the count in Figure 1.

2. Now submerge your hand in a dishpan of water to which has been added

snow or ice so that the temperature is near the freezing point. Leave your

hand in the water for one full minute.

3. Remove your hand and immediately count how many forceful fists you can

make in 20 seconds. Record in Figure 1.

Figure 1: Effect of Temperature on Muscle Action

Temperature	Number of Fists
Normal	30
Ice Water	15

Effect of Fatigue on Muscle Action

1. Count how many times you can tightly squeeze a rubber ball in your hand

in 20 seconds. Record in Figure 2.

2. Repeat the squeezing nine more times and record results. Do not rest

between trials.

(An alternative procedure which works well is to open and close a

clothespin with the thumb and index finger while the other fingers are held

out straight.)

Figure 2: Effect of Fatigue on Muscle Action

Trial	# of Squeezes in 20 seconds	9 More X's
1	33	8 sec
2	28	8 sec
3	25	9 sec
4	22	10 sec
5	20	11 sec
6	19	12 sec
7	18	12 sec
8	18	12 sec
9	16	13 sec
10	15	13 sec

ANALYSIS OF DATA:

1. What are the three changes you observed in a muscle while it is working (contracted)?

I observed the longer into the experiment I went the harder it was to physically close my hand, my hand got warmer, more muscle burn at the end (lactic acid build up), had to concentrate more to close my hand tightly, and the interval was longer between fists.

2. What effect did the cold temperature have on the action of your hand muscles? Explain.

The cold made my hand slow to react as well as unable to make as tight of a fist. I have always been told as an athlete to “warm up my muscles by stretching and light exercise before competing”. Warm muscle work better than cold muscles due to increases blood flow (O2 and glucose).

Attempts Number

4. What effect did fatigue have on the action of your hand muscles? Explain.

At a certain point the number of repetitions exceeded the aerobic threshold causing an anaerobic process to start, and lactic acid started building up.