Experiment #5
Strength measurement and static work capacity
Objectives:
1. To measure the maximum voluntary contraction (MVC) for a muscle group.
2. To find the relationship between the maximum voluntary contraction and the
endurance time in a static muscle contraction.
3. To measure MVC at different hand – wrist – arm configuration.
4. To study the factors that affect on the value of the MVC.
Background:
Muscles comprise about 40% of the weight of the body; the most important
characteristic of muscle is its ability to shrink to half its normal length (muscular
contraction). Each muscle fiber contracts with a certain force, and the strength of the
whole muscle is the sum of these muscle fibers. The person’s inherent muscle strength
depends in the first instance on the cross section of his or her muscles.
Strength can be measured either of two conditions: dynamic conditions, when the
body member is actually being moved, and static conditions, when the force is
applied against a fixed object, with no displacement of the body member.
During static muscular effort the blood vessels are compressed by the internal
pressure of the muscle tissue, so that blood no longer flows through the muscle.
During dynamic muscular effort, on the other hand, the muscle acts as a pump in the
blood system. Compression squeezes blood out of the muscle, and the subsequent
relaxation releases a fresh flow of blood into it. By this means the blood supply
becomes several times greater than normal.
Picture ( static and dynamic) blood flow
Maximum voluntary contraction (MVC) is a static strength measure which is the
maximum force exerted isometrically in a single voluntary effort. Strength depends on
a large number of variables. Some of these variables are the overall body posture, the
joint angle of the body parts involved in the activity, and the point of application of
the force. Other important factors are the level of motivation and the instructions
provided to the subject.
The ability of people to maintain a given muscular force is related to the magnitude of
the force. So Endurance is the time duration for which we can do a job.
It is obvious that people can maintain their maximum force very briefly, were as they
can maintain a force of around 25% or less of their own force for some what extended
period.
Equipments
Hand Dynamometer : (figure 1)
This device has two scales
The first scale is index for the force (in Kg).
Its range (0-100) Kg.
The second one measures the grip span(in
mm)
Figure 1: Hand Dynamometer
Stop watch:
Goniometer :
To measure and control the joint angle
Procedure:
1. Subjects are request to sit in an adjustable chair. Te elbow angle at 90 degree
with the forearm resting on the arm support. (use goinometer to measure the
angle)
2. each subject should exert at the MVC force for 5 seconds then rest for one
minute and repeat trials for three times.
3. Calculate the average of the three trials to obtain the MVC for each subject.
4. Repeat steps 1, 2, and 3 for an ulnar and radial deviation for each subject.
5. Make sure that the subjects are performing the experiments at a power grip
and record the grip span for each subject.
6. fill the data in the tables (1,2,3) below
7. For the endurance part calculate 20%, 40%, 60%, and 80% of MVC for each
subject and ask him or her to grasp at each level as long as he or she can,
while being comfortable and feeling no pain or fatigue. ( fill the calculations in
tables 4, and 5 ).
Neutral
MVC
Grip
Name gender Age Trial Trial Trial average SD CV
span
1 2 3
Ulnar
MVC
Name Average SD CV
Trial 1 Trial 2 Trial 3
Radial
MVC CV
Name Average SD
Trial 1 Trial 2 Trial 3 Trial 1
Name Average(MVC) 20% MVC 40% MVC 60% MVC 80% MVC
Endurance for different percent of MVC
Name
20% MVC 40% MVC 60% MVC 80% MVC
Analysis:
1. Show how repeatable are the MVC values for each subject using the
coefficient of variance.
2. If the group consists of male and female, then study the gender effect on the
MVC.
3. If the group consists of male and female, then find the gender effect on the
endurance time.
4. Plot MVC values versus grip Span.
5. Plot the MVC at the different wrist deviation.
6. Plot the MVC versus endurance time.
7. Perform a survey of the literature. Observe and identify a job that has a static
work element (i.e. standing or sitting in a position). Make suggestions to
reduce the amount of static work in the job discussed if possible.
8. What is the source of error in this experiment?