1. Lessons 20 & 21 Muscle Strength & Fatigue
Human Body Systems
Lessons 20 & 21
Muscle Strength & Fatigue

2. Muscle Power!
More than a few. The human body has more than 650 muscles.
Unique in its own way. No two muscles in the body have exactly the same function. When one muscle is paralyzed, either stability of the body part is impaired or some specific movement is lost.
Watch your step. Forward locomotion such as walking or running is actually the process of losing and catching one's balance.
Boost your burning power. Did you know that for every 1 lb of muscle you gain, your body burns an extra 50 calories a day? If you can turn at least 5 lbs of extra "fat" into muscle, you will automatically burn an additional 250 calories per day.
A mini-Charles Atlas. Muscles are comprised of muscle fibers. Each fiber is thinner than a human hair and can support up to 1,000 times its own weight.
Use it or lose it. By age 65, people who haven't engaged in regular exercise may incur a decrease in their muscular strength level by as much as 80%.
Make your move. A muscle moves by contracting and by its motion, you move. As a machine for moving, a muscle is pretty efficient, using about 35-50% of its potential energy.

3. Say Cheese! You use 14 muscles to smile and 43 to frown.
Muscles normally account for 40% of one's body weight.
You have over 30 facial muscles which create looks like surprise, happiness, sadness, and frowning.
Eye muscles are the busiest muscles in the body. Scientists estimate they may move more than 100,000 times a day!
The largest muscle in the body is the one you sit on!

4. How do muscles move?
Muscles that move your bones work in pairs. When one contracts, the other must relax. For example, your bicep must relax and lengthen when your triceps contract and shorten.

5. Types of muscles
Cardiac
Skeletal
Smooth
Heart
Voluntary
Involuntary

6. How can you measure muscle strength?

7. The investigation
Today, we are going to investigate the strength of 3 arm muscles:
Biceps
Triceps
Forearm
Take out a piece of notebook paper and title it MUSCLE LAB
Don’t forget to put your name, date, and period on the paper!

8. Create Data Collection Tool
Muscle Group
Rank strongest to weakest 1-3
Trial 1
Force (N)
Trial 2 Force (N)
Average
Biceps
Triceps
Forearm
Before we start, guess which muscle is the strongest. Rank each muscle from 1 – 3 with 1 being the strongest. Fill in the first column.

9. Working in groups, take turns completing each task
Working in groups, take turns completing each task. Your partners will read the scale for you.
Calibrate your scale to 0.
You will measure Force in Newtons (N).The scale is calibrated in Kilograms (Kg). To get Newtons, multiply Kg by 10.
Biceps: place scale under desk; push up
Triceps: place scale on desk; press with your hands – not your arms.
Forearms: Grab scale as hard as you can – do not use your thumbs
After each measurement, record your force. Remember to multiply your Kg by 10.
Repeat 2 times for each muscle and then find average.
Rank the muscles again by actual strength based on your results.

10. What can we do to strengthen our biceps, triceps, & forearms?
Brainstorm of an activity we can do at the beginning of class each day.
We will do one exercise for each muscle each day for a month and repeat the Muscle Lab to see if we can increase our strength.

11. Now let’s measure muscle fatigue

12. Muscle Fatigue What causes muscle fatigue?
Can you do anything to prevent it?
How long can your muscles endure?
Muscle fatigue is a muscle’s reduced ability to generate force.

13. How long can you last? Stand up. Each person take 1 textbook.
When the timer starts, hold the textbook in your hands, palms should be flat and facing; arms should be straight and held in front of you at shoulder length.
Sit down when your arms get too tired to hold the book out in front of you.
Click here for the timer

14. Which sport is the toughest?
Place the following sports in a list from 1 – 11 (1 being the toughest). Sports should be evaluated on endurance, strength, power, speed, and eye-hand coordination.
Basketball Baseball/Softball Boxing Football Gymnastics Ice Hockey Martial Arts Skiing: Alpine Soccer Tennis Wrestling
Click here to see ESPN’s ranking of the toughest sports
Here are ESPN’s answers
1. Boxing 2. Ice Hockey 3. Football 4. Basketball 5. Wrestling 6. Martial Arts 7. Tennis 8. Gymnastics 9. Baseball/Softball 10. Soccer 11. Skiing: Alpine

15. Directions Read pages 174-176 in the Human Body Systems Book.
Follow the directions. Make sure to create a data collection tool to collect your data (#2)
When you have finished collecting your data, graph your data as instructed (#6)
Answer the questions on page 176 (#7 – A, B, & C.)
Read Anabolic Steroids page 173 and Repetitive Stress Injury page 177 & 178.