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Skeletal and Muscle Biomechanics
11
M ATERIALS
•
hand dynamometer
•
human skeleton
•
Tape measure and blood pressure cuff
•
textbook and lecture notes for reference
O BJECTIVES
Upon the completion of these laboratory exercises, you should be able to:
1.
Identify various the various muscle fiber types and how they function in the human body.
2.
Understand how different exercises influence the type of muscles fibers utilized
4.
Understand both active and passive insufficiency and examples of each in human motion.
5. Understand the types of lever systems in the body and how to apply them.
E XERCISE 1. M USCLE F IBER TYPES AND M ETABOLISM
A majority of the body’s muscle is skeletal muscle. Skeletal muscles are multinucleated tissues and
have several important functions in the human body. They enable the body to move (locomotion) and
keep the body upright against gravity. They also generate heat through their contractions that aid in
maintaining the body’s temperature. The skeletal muscle cells are long, cylindrical, and
multinucleated. Since skeletal muscles attach to the skeleton, it will directly affect the bones and
joints associated with the skeleton. This type of muscle is the only muscle under voluntary control.
There are over 600 of these muscles in the human body. Look at the cross section of the muscle.
Notice the individual muscle fiber, which is wrapped in areolar connective tissue called
endomysium. Several of these fibers are wrapped in a stronger collagen membrane called
perimysium. The bundle that is created is called a fascicle. All the fascicles are wrapped in dense
connective tissue called the epimysium. This will become continuous with the tendons of the
muscles. There are histological differences between the individual muscle fibers. Skeletal muscle is
composed of a heterogeneous collection of 3 different types of muscle fibers. Their classifications are
based on histological differences, speed of muscle contraction, and the preferred method of ATP
production. A cross section of skeletal muscle allows the 3 different muscle fiber types to easily be
visualized (Figure 1).
Slow oxidative fibers (Type 1) contain greater amounts of mitochondria and myoglobin (oxygenbinding protein) and limited glycogen stores, making aerobic respiration their preferred form of
metabolism. These fibers are adapted for activities that require endurance and are resistant to
fatigue. They are found in higher concentrations in the muscles responsible for maintaining posture
and balance. These types of muscle fibers are dominant in the muscles of the back and neck.
Fast glycolytic fibers (Type 2B) are rich in enzymes for the phosphagen–glycogen–lactic acid
systems. These enzymes are adapted for producing ATP quickly by glycolysis. They contain fewer
mitochondria, which makes them more susceptible to fatigue. They store higher concentrations of
glycogen, making them suited for anaerobic metabolism. These muscles are adapted to hydrolyze
ATP faster, which increases contraction speed. They are beneficial for movements that require speed
and power. The extraocular eye muscles, gastrocnemius, and biceps brachii contain higher
percentages of these fibers.
Fast oxidative fibers (Type 2A) contain characteristics of both slow twitch type 1 and fast twitch 2B
fibers. They can hydrolyze ATP rapidly for energy yet they also have increased mitochondria, making
them moderately resistant to fatigue. These fibers usually make up about 10% of the total muscle
fibers. However, this number may vary based on the individual’s genetics. Type 2A fibers in
individuals who train aerobically will develop more of the characteristics consistent with the slow
oxidative Type 1 muscle fibers. Type 2A fibers in individuals who train anaerobically will develop
more of the characteristics consistent with the fast glycolytic Type 2B muscle fibers.
Muscle fatigue is the state when the muscle loses its ability to contract. It occurs during exercise
when ATP production fails to keep pace with ATP requirements of the muscle. The result is elevated
levels of lactic acid. If sufficient quantities of oxygen are not present in the mitochondria, respiration
is halted and anaerobic metabolism will be the preferred source of ATP production. The buildup of
lactic acid reduces the pH within the muscle. This interferes with its ability to contract. Excessive
levels of lactic acid are also responsible for the burning sensation felt during exercise. Contrary to
popular belief the soreness that is felt 24 to 48 hours after exercising is not due to lactic acid
production. It is believed that the soreness is caused by microscopic damage to the muscles. This is
also referred to as DOMS (Delayed Onset Muscle Soreness).
FIGURE 1.
Type 1 muscle fibers stain the darkest because of their high concentrations of the oxygen-binding
protein myoglobin. The high density of capillaries found in this type makes them adapted for aerobic
respiration. Notice the Type 2B fibers’ relative light color. These fibers contain a diminished vascular
supply and have low levels of myoglobin. They are designed for anaerobic respiration. Type 2A fibers
also have a red appearance due to their increased vascularity and myoglobin content.
This experiment will look at 2 similar exercises:
1.
Have the subject sit in a chair holding a dynamometer in their left hand
2.
Squeeze the dynamometer as hard as possible. Record the maximum grip strength produced.
Repeat this procedure for the right arm.
Maximum left: _________________ psi
Maximum right: _________________ psi
3.
Have the subject count the number of repetitions to completely fatigue their forearm muscles
while repeatedly squeezing the hand dynamometer at 75% maximal grip strength. For example,
if the maximum grip strength was 20 psi, repeatedly squeeze the grip at 15 psi until completely
fatigued. Record the number of repetitions in Table 1.
4.
Place a blood pressure cuff on the proximal forearm. Inflate the cuff to 150 mm Hg. Repeat the
activity in step 3. Record the number of repetitions in the table below (Table 1)
5.
Take a 2-minute break prior to starting this next step.
6.
Record the time to fatigue the left forearm muscles by holding the hand dynamometer at 100%
of maximal grip strength (static hold). Record in the table below (Table 1).
7.
Inflate a blood pressure cuff to 150 mm Hg on the proximal forearm. Repeat the activity in step 6.
Record in the table below (Table 1)
TABLE 1
Grip Activity Type
Repetitions to Fatigue
Left hand dynamometer with repetition
Right hand dynamometer repetition with blood pressure cuff
Grip Activity Type
Time in Seconds to
Fatigue
Left hand dynamometer with static hold
Right hand dynamometer static hold with blood pressure cuff
1.
Which of the following activities caused the muscles of the forearm to fatigue the fastest? Explain
why.
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
2.
What effect did the blood pressure cuff have on muscle fatigue?
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
a.
What does this imply about blood flow and onset of fatigue?
__________________________________________________________________________________________________________
__________________________________________________________________________________________________________
b.
Which metabolic pathway would be preferred for ATP production when blood flow is
reduced?
__________________________________________________________________________________________________________
__________________________________________________________________________________________________________
c.
What muscle fiber type would be adapted for periods of reduced blood flow? __________________
__________________________________________________________________________________________________________
__________________________________________________________________________________________________________
3.
Which activity was most resistant to fatigue?
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
a.
What would be the preferred muscle fiber type for this activity?
__________________________________________________________________________________________________________
__________________________________________________________________________________________________________
b.
What is the preferred metabolic pathway for ATP production for this activity? _________________
__________________________________________________________________________________________________________
__________________________________________________________________________________________________________
Exercise2.
A
B
C
1. Have the exercise subject perform a static (holding) squat position where the
thighs are just short of parallel. (Position A) Record the time that they can
maintain this position.
2. Give the exercise subject a three-minute break.
3. Now perform a traditional full squat in which the subject’s legs move through
the full range of motion demonstrated by the illustration. (Transition though all
positions) The traditional squat should be done at a comfortable pace. In the
following chart, record the time it takes for the subject to fatigue during this
activity.
Squat Type
Time in
Seconds to
Fatigue
Metabolic
Pathway
Used
Dominant
Muscle
Fiber Type
Traditional
squat
Static (hold)
squat
1.
Which type of squat will the subject be able to do longer?
_________________________________________________________________________
2.
Which type of squat will require a larger number of muscle fibers to
contract?
_________________________________________________________________________
a. What effect will the increased number of muscle fibers required have on the
blood supply to the muscle? (Hint: Will contractions of more muscle fibers
compress the blood vessels or allow for adequate blood flow?)
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
b. What effect will this have on the metabolism of the muscle (anaerobic vs.
aerobic)?
____________________________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
c. What muscle fiber type muscle fiber will be preferred for this activity?
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
d. What type of muscles fibers would you expect a world class sprinter might
naturally have a greater percentage?
__________________________________________________________________________
__________________________________________________________________________
e. What type of muscles fibers would you expect a world class marathon runner
might naturally have a greater percentage of ?
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
Exercise 3.
Active vs. Passive Insufficiency
1. When a multi-joint muscle contracts simultaneously over 2 joints the muscle is unable to generate
a maximum muscle contraction is an example of?
______________________________________________________________________________________________________________
2. Agonist muscle unable to reach full range of motion because of inadequate length of antagonistic
two joint muscle is an example of:
______________________________________________________________________________________________________________
3.
Test the isometric strength of wrist flexors.
1. Make a fist while your hand is in a neutral position. °
2. Measure the grip strength with a hand dynamometer. Record the number in the table below.
3. Repeat the procedure with your wrist flexed 45° Record in the table below.
4. Repeat the procedure with your wrist extended 45° Record in the table below.
5. The muscles involved are the finger and wrist flexors and extensors. Determine which
muscle group is an example of either active or passive insufficiency. Record in the table
below.
6. Which position was the grip strength the greatest? Explain
______________________________________________________________________________________________________________
_____________________________________________________________________________________________________________
______________________________________________________________________________________________________________
Position
Wrist Neutral
Wrist Flexed 45°
Wrist extended 45°
Grip strength (PSI)
Finger/wrist Flexors
Finger /wrist extensors
6. Lie prone on your stomach and flex your knee as much as possible. Why can’t your heel touch
your buttocks? (Which muscles are responsible for flexing your knee? Which muscle is limiting
it? Is this active or passive insufficiency? ________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
7. Test the person’s knee flexion strength while in prone with knee in a maximally flexed
position. Repeat the procedure by placing a towel under the thigh. What effect does this have
on the muscles ability to generate strength? _______________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
8. Test the person’s knee flexion strength bending over the table at with their hip flexed at a 30°.
What effect does this have on the muscles ability to generate strength? Explain ________________
__________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
9. Which machine would the biceps be able to create more force? Explain.
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
______________________________________________________________________________________________________________
E XERCISE 2. A N ATOM ICAL L EVERS
In order to understand how human movement occurs, an appreciation of basic biomechanics
relating to lever systems is necessary. Levers are rigid objects that can multiply the mechanical
force (effort) that can be applied to another object or resistance force (load). The joints of the
body function as the fulcrum or axis for anatomical movement. The classification of levers is
determined by the arrangement of three specific points. They include the fulcrum, effort arm,
and resistance arm. The fulcrum is the fixed point that the lever rotates around. The effort arm is
the distance between the fulcrum (joint) and the muscle attachment (insertion). The resistance
arm is the distance between the fulcrum and applied force. This is the weight or load the effort
arm has to overcome. A measurement of how efficient a lever is in moving an object can be
expressed as its mechanical advantage (effort arm/resistance arm). In general, lever systems
can either favor force or speed. If the mechanical advantage is <1, speed will be favored. If it is
>1, force will be favored. The human skeleton with all of its bones, ligaments, and muscles form
functional levers for the body to create movement. There are 3 major types of anatomical lever
systems in the body (Figure 2)
The first-class lever system is where the fulcrum is in the middle. The nodding motion of the
head is considered a first-class lever system. If the fulcrum moves closer to the resistance arm,
force is favored (the effort arm > resistance arm). The longer the force arm, the easier it is to do
work (greater force produced with the same muscle exertion). These are the most efficient class
of levers.
A second-class lever system has two distinct features. First, the resistance and effort arm are
on the same side of the fulcrum. Second, the resistance arm is closer to the fulcrum. This type of
system favors force production over speed. The wheelbarrow demonstrates a second-class lever
system. They are rare in the human body. Standing on one’s tippy toes (plantar flexion) or
performing push-ups are examples of activities that take advantage of second-class lever
systems.
In third-class lever systems the resistance and effort arm are also on the same side of the
fulcrum with the effort arm being closer. Lifting a carton of milk and shoveling are examples of
third-class levers. Most of the joints in the human body function as third-class lever systems.
These systems favor speed over force.
FIGURE 2
LEVER SYSTEM EXPERIMENT
1. Measure the distance between the acromion process of the scapula and the insertion of the
deltoid muscle on the humerus (effort arm). Record in Table 2 under (D2). It will remain the
constant throughout the experiment.
2. Place an ankle weight in the subject’s hand. Measure the distance from the shoulder joint
(acromion process) to the ankle weight held in the subject’s hand. This provides the
resistance arm. Record in Table 2 under (D1 ) for hand.
3. Calculate the mechanical advantage: (effort arm/resistance arm) = (D 2)/(D1 ) (Show work.)
4. Now have the subject repeatedly abduct their arm to 90° while holding the weight in their
hand until their deltoid is completely fatigued. Record the number of repetitions in Table 10.5.
5. Let the subject rest their arm for 3 minutes. Measure the distance from the acromion process
to the elbow. This provides the resistance arm. Record in Table 2 under (D1 ) for elbow.
6. Calculate the mechanical advantage: (effort arm/resistance arm) =(D 2)/ (D1 ) (Show work.)
7. Now with the weight wrapped around their elbow, have them repeatedly abduct their arm to
90° until their deltoid is completely fatigued. Record the number of repetitions in Table 2
8. Calculate the force produced by the deltoid, both when the weight is held in the hand and
when wrapped around the elbow (F2). Use the following equation.
F1 × D1 = F2 × D2 (Show work.)
F1 = weight of the resistance
D1 = length of the resistance arm
F2 = the force produced by the muscle
D2 = length of the effort arm
TABLE 2
Ankle
Weight
lbs (F1)
Effort
Arm
(cm)
(D2)
Resistance
Arm (cm)
(D1)
Mechanical
Advantage
Muscular
Force
Produce
d (F2)
Repetitions
to Fatigue
Hand
Elbow
ANATOMICAL LEVER QUESTIONS
1.What type of lever system does this activity test? ____________________________________
2. What effect does doubling the length of the effort arm (D2 ) have on the muscular force
produced? (Show work.)
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
3. What relationship did the length of the resistance arm have on both mechanical advantage
and muscular force produced? _________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
5. Define the anatomical lever system for the following activities: Draw in the Axis, load and
effort.
a. Skull crusher ________________________________________________________________
b. Bench press: _________________________________________________________________
C:
Calf rises: Do the same lever systems apply for both machines ?Explain.
__________________________________________________________________________
__________________________________________________________________________
Do these machines isolate specific muscles? Explain.
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
Which anatomical lever system is used with the muscles identified in the previous question? ____
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
Are standing on ones tippy toes and pressing on a gas peddle the same lever system? Explain ______
__________________________________________________________________________
__________________________________________________________________________
D: Latissimus pull down: _________________________________________________________