Experiment 5: ATP and Muscle Fatigue
Muscles require energy to contract. Energy is released when biomolecules such as sugars and fats are broken down, and is stored in the form of ATP. ATP enables muscle contraction, but can only be stored in relatively small amounts. For this reason, the body must continually metabolize new ATP molecules.
Muscle fatigue occurs if the local ATP reservoir for a muscle becomes depleted. This is a common result of strenuous exercise in which ATP is consumed at a faster rate than it is produced. At this point, muscles may fail to contract and the intensity of an exercise must decrease. In this experiment, you will test how long it takes your muscles to fatigue.
| Materials Stopwatch *Participant *Sturdy Wall to Stand Against | *You must provide |
Procedure
1. To begin, find a wall that is strong enough for you to push against. A temporary wall (such as a partition panel) is not suitable.
2. Find the stopwatch and adjust the settings so it is ready to operate.
3. Stand with your back pressed up against the wall, and lower yourself into a “wall-sit”. To do this:
a. Align the backs of your heels, hips, and shoulders with the wall.
b. Keeping your back pressed against the wall, take a few small steps forward (your upper half will lower as you walk your feet out).
c. Lower yourself into a sitting position, keeping your back flat against the wall, until your knees form a 90 degree angle.
d. Steady this position by focusing the majority of your weight in your heels. Do not allow your lower back to pull away from the wall.
4. Start the stopwatch and time how long you are able to hold the wall-sit position. The amount of time will vary, but will likely fall within approximately 30 – 120 seconds. When you are tired, check the time on the stopwatch, and move out of the position by slowly lowering your body down to the floor or standing up.
5. Record how long you were able to hold the wall-sit in Table 3.
6. Allow your muscles to rest for approximately two minutes, reset the stopwatch, and repeat Steps 3 – 5.
7. Again, allow your muscles to rest for approximately two minutes, reset the stopwatch, and repeat Steps 3 – 5. You should have three trials of data.
| Table 3: Muscle Fatigue Data | |
| Trial | Time (seconds) |
| Trial 1 | |
| Trial 2 | |
| Trial 3 |
Post-Lab Questions
1. What happened to the time intervals between Trial 1 and Trial 3? What caused this change?
2. Identify three muscles which were engaged during the wall-sit.
3. Explain the biochemical reasoning behind muscle fatigue.
