Physiology – Muscle Planning Lab
Work with a partner to collect some data about either the arm muscles, leg muscles or abdominal
muscles. You will need to choose an independent variable, dependent variable and be sure to have
controls. Be sure that your variables are quantitative (can be measured numerically) so that you are able
to produce an x-y scatter plot of your data, look for a trend, explain the trend (or lack thereof). You will
be marked using the 78 point lab report rubric. So, be sure to have a hypothesis before you start and a
list of materials and a procedure that I will check before you begin! The following information may be
helpful:
Skeletal Muscle Contraction
Skeletal muscles are attached to bone on each end by tendons. This attachment causes bones,
and thus body parts, to move when our muscles contract. Furthermore, the nature of the
attachment affects the efficiency of movement in terms of strength, speed and distance moved.
Muscles work by way of lever systems which is a rigid lever, such as a bone, that moves on a
fixed point called a fulcrum.
A teeter-totter is a good example of a lever system. The weight of each person on either side
represent the force and load, while the pivot in the middle represents the fulcrum. If the fulcrum
is in the middle of the board, two people with the same weight will balance the board.
Moving the board relative to the fulcrum will result in unbalance, making it easier for one person
to push the other up. Just as moving the fulcrum of a teeter totter can increase the effectiveness
of a force, the nature of muscle attachment to bone relative to the joint increases the efficiency of
muscle contraction and thus, body movement. A lever moves when a force (F), or effort, is great
enough to overcome a load (L), or resistance, that would otherwise resist movement. This lesson
describes the three basic lever systems utilized by our muscles and bones for body support and
movement.
First-Class Lever
Let's take a look at first-class levers. While the body has relatively few first-class levers, they
are easy to understand as they resemble a teeter-totter. In such a lever, the load is located on the
opposite side of the fulcrum as the applied force.
For example, head extension is a good example of a first-class lever system. Here, neck and
back muscles apply an force to move the head. The weight of the head it the load, and the
fulcrum is the joint between the skull and the vertebrae.
Second-Class Lever
Let's move on to second-class levers. In a second-class lever, the load is located between the
force and the fulcrum. A wheel barrow is great example of a second-class lever system. Here, the
wheel is the fulcrum, or the pivot point, the weight is the load and lifting the handles applies the
force to move the load.
What about in the body? Plantar flexion, or standing on balls of our feet, is an example of a
second-class lever in the body. Here, the ball of the foot is the fulcrum, the weight of the body is
the load, and the contraction of the calf muscles provides a lifting force, or effort. This type of
system allows a small force to move a relatively large load. In fact, moving the force further
away from the load increases the strength of the lever system. However, speed and distance of
movement are compromised at the expense of this increased strength. In other words, a relatively
small force moves a large load a relatively short distance and moves it slowly.
Plantar flexion is an example of a second-degree lever
Third-Class Lever
Now let's talk about third-class levers. Third-class levers are the most common in the human
body. Here, the force is applied between the load and the fulcrum. A broom is a good example of
a third-class lever where the hand on top of the broom represents the fulcrum, or the pivot point.
The force is applied in the middle of the broom by your other hand, which will then move the
broom (the broom being the load).
An example of a third-class lever in the body is forearm flexion, where the elbow is the
fulcrum, the biceps apply upward-directed force to the forearm. The load is the forearm itself and
anything that may be held in the hand.
Forearm flexion allows a load to move faster, but requires more strength