Muscle Fatigue

Bones and organs are moved by contractile muscle tissue, of which there are three types: skeletal, smooth, and cardiac. Skeletal muscles, those responsible for moving parts of the body that are under voluntary control, are made up of muscle fibers. Each muscle fiber is an elongated, multinucleated cell crossed by dark and light striations, and the fibers are grouped into bundles called fascicles. Generally, the muscle fibers span the length of the muscle and are woven into connective tissues like tendons at the end of the muscle. The tendons attach the muscle to the bone, allowing it to function as a biological lever that can exert force on the bone it attaches to. The more fibers a muscle has, the more powerful the muscle is: for example, the quadriceps has a huge number of fibers, so it is one of the most powerful muscles in the body.

Every skeletal muscle is supplied with at least one nerve, one artery, and one vein. This is to ensure that every muscle can receive incoming nerve impulses while being fueled by fresh blood from the arteries. The veins are needed to export deoxygenated blood containing metabolic wastes and other byproducts. Active muscles require energy, and therefore require a continuous supply of oxygen and nutrients. For fuel, muscles rely on glucose form the bloodstream, glycogen stored in the muscle fibers, or fat molecules during vigorous, prolonged exercise. When energy availability fails to keep pace with the demands being placed on the muscle, the muscle will lose its physiological ability to contract in a controlled fashion due to ATP depletion. Even though the muscle may still receive nerve stimulation to move, muscle fatigue sets in.

For each lab group:

• Force Sensor:
     PASPORT (PS-2104)   |   ScienceWorkshop (CI-6746)
• Computer Interface:
     PASPORT: Xplorer GLX (PS-2002)  |  Xplorer (PS-2000)  |  USB Link (PS-2100A)  |  PowerLink (PS-2001)
     ScienceWorkshop: 500 Interface (CI-6400)
• Container of cold water
• Ice

1. Click on one of the links below to download a pre-configured DataStudio file for this force experiment, and then open the file.
   
   PASPORT users: Windows (.zip file) or Macintosh (.sit file)
   
   ScienceWorkshop 500 users: Windows (.zip file) or Macintosh (.sit file)
   
   When the file is opened, you should see a graph display of Force vs. Time, as well as a digits display of force.
   
   
2. Connect the Force Sensor to an Xplorer or USB link (PASPORT users), or plug the sensor into the 500 Interface (ScienceWorkshop 500 users).
   If you are using the ScienceWorkshop 500 Interface, be sure the sensor is associated correctly in the Experiment Setup window when you open the DataStudio file.
   
   
3. Be sure the rubber bumper (included with the sensor) is screwed into the sensor.
   

Data Recording:

1. Place the ice into the container of cold water, and let stand until the water temperature is about 4 degrees Celsius.
   
   
2. Grip the Force Sensor and place your thumb on the rubber bumper.
   
   
3. Click the Start button ( ) to begin collecting data.
   
   
4. Begin squeezing the Force Sensor until the DataStudio graph display reads 40N or above.
   
   
5. Continue to hold the Force Sensor at or above 40N as long as possible.
   
   
6. Click the Stop button ( ) once the display begins to drop below 40N.
   
   
7. Submerse the same hand into the container of ice water for 30 seconds or more.
   
   
8. Repeat steps 2-6.

1. Which of the two endurance tests were longer in length of time?
   
   
2. What factors may have caused different results?
   
   
3. What effect did the ice water have on the action of the student’s hand muscles? Why?
   
   
4. Discuss how this experiment relates to the experience of drowning victims who succumb in very cold water as opposed to warmer waters.