Biology Forums - Study Force

Hi, would anyone have the answers for the Skeletal Muscle lab in PhysioEx 8.0 for:

Activity 7:
4. Why does the force begin to decrease with time? Note that a decrease in force indicates muscle fatigue.

Activity 8:
7. What happens to the passive and active forces as the muscle length is increased from 50 mm to 100 mm?
Passive force:
Active force:
Total force:
Explain the dip in the total force curve. (Hint: Keep in mind you are measuring the sum of active and passive forces.)

Activity 9:

5. What do you see happening to the muscle during the flat part of the tracing? Click Stimulate to repeat if you wish to see the muscle action again.
6. Return the 0.5-g weight to the cabinet. Drag the 1.5-g weight to the muscle. Click Stimulate,  and then click Record Data.
Which of the two weights used so far results in the highest initial velocity of shortening?
Weight g
Velocity mm/sec
7. Repeat step 6 for the remaining two weights.
Weight ________________ g
Velocity _______________ mm/sec
Weight ________________ g
Velocity _______________ mm/sec
9. What does the plot reveal about the relationship between resistance and the initial velocity of shortening?
15. Describe the relationship between starting length and initial velocity of shortening.

Content hidden

Thank you! :)

Activity 7

Why does the force begin to decrease with time? Note that a decrease in force indicates muscle fatigue.

ATP is being consumed by the muscle faster than it is being produced.

Turning the stimulator off allows a small measure of recovery. The muscle will produce force for a longer period if the stimulator is briefly turned off than if the stimulations were allowed to continue without interruption. Explain why.

The muscle then can catch up with ATP production.

Describe the difference between the current tracing and the myogram generated in step 6.
The second tracing shows faster fatigue than the tracing with the stimulator turned on and off.

Activity 8

What happens to the passive and active forces as the muscle length is increased from 50 mm to 100 mm?
Passive force: it starts at 0 then it increases sharply at 84mm
Active force: increases steadily until about 75mm, then falls with increased length
Total force:  At first it rises, then it begins to fall at 76mm, then at 94mm it starts to rises again causing a dip in the curve.

Explain the dip in the total force curve. (Hint: Keep in mind you are measuring the sum of active and passive forces.)
There is a rise on the left side of the total force because of the rise in active force (passive force has no influence on this). When the force curve begins to fall it is because the active force falls. The total force does not fall as fast as the active force because the passive force is simultaneously raising. The increase at the right of the total force curve is basically because of the passive force.

Activity 9

What do you see happening to the muscle during the flat part of the tracing? Click Stimulate to repeat if you wish to see the muscle action again.

Muscle rises from the surface of the platform and then descends again.

Does the force the muscle produces change during the flat part of the tracing (increase, decrease, or stay the same)?

No. It stays the same.

Which of the two weights used so far results in the highest initial velocity of shortening?
Weight _________ g
Velocity __________mm/sec

Weight: 1.5g  Velocity: 0.45mm/sec


Repeat step 6 for the remaining two weights.
Weight ________________ g
Velocity _______________ mm/sec
Weight ________________ g
Velocity _______________ mm/sec

Weight: 1.0g Velocity: 1.34mm/sec
Weight: 2.0g Velocity: 0.00mm/sec

What does the plot reveal about the relationship between resistance and the initial velocity of shortening?
As the resistance increases the initial velocity of shortening decreases.

Describe the relationship between starting length and initial velocity of shortening.

The length is increased from 60mm to 90mm by increments of 5mm. The initial velocity of shortening increases at first, then it decreases.

Thanks for your help! :)

You're very welcome!!  :)

so helpful!

Thanks!!