Download I. Introduction: Muscle Contraction

PEAK 404 - LAB 4:
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PEAK 404
EXERCISE PHYSIOLOGY
LAB 4
Muscle Contraction, Function, and Fiber Type Estimation
I. Introduction: Muscle Contraction
Voluntary contraction of skeletal muscle is the result of neural, chemical, and
mechanical events that are subject to different levels of control. The neural
control involves the execution of events planned in the motor cortex of the brain
with the signal relayed to the muscle cell via axons in the spinal cord and neurons
going from the spinal cord to the sarcolemma. A signal of sufficient strength
arising from an external origin (electricity) will cause the chemical and mechanical
events necessary to elicit a muscle contraction but without the coordination and
refinement found in typical human movement.
Lab Activity IA.
Each person in the group can act as a subject for this portion of the lab. Great care
will be taken to ensure the safety and comfort of each subject. The subject will
have two electrode pads placed on the forearm for the purpose of applying a mild
electrical stimulation to the extrinsic muscles of the wrist and hand. Only enough
current needed to elicit a contraction that flexes fingers will be used. A stronger
current will generate enough muscular force to cause wrist flexion. Current
stronger than this is uncomfortable and not recommended. Alter electrode
position as needed and to target the muscles that move specific fingers.
Lab Assignment 1A.
1) Describe the sensation you felt as a result of external stimulation for muscular
contraction. 2) Describe the chemical and mechanical events that were initiated by
the electrical stimulation (excitation-contraction coupling).
II. Introduction: Muscle Function
The properties of skeletal muscle are such that their maximal function is limited
under certain conditions. The Length – Tension Relationship, describes one of
these conditions. The result of both maximally shortened muscle and maximally
lengthened muscle is a decrease in force output regardless of the type, size,
strength, or location of the muscle. The purpose of this part of lab is to observe
the impact contraction length has on force production.
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Lab Activity IIA.
All students will be used as subjects. You will complete the following task under
three conditions: normal wrist extension, full wrist flexion, and full wrist
hyperextension. While holding the handgrip dynamometer, measure and record
the force of your maximal grip effort during the above wrist positions. Record the
grip data from each subject in class in a table separating male and female results.
Lab Assignment IIA.
1) Calculate the average force produced by male and by female students under
each wrist position condition and report in a “presentation” table labeled and
referred to appropriately. 2) Plot the data in a column graph comparing full flexion
and full extension to normal extension. Plot the data from male and female
subjects on the same graph. Title and label the graph appropriately.
Lab Assignment IIB.
1) From the data and your graph, describe the impact each wrist position condition
had on force production in men and in women and 1) explain the reason for this
phenomenon.
III. Introduction: Estimation of Muscle Fiber Type
Distributed within each muscle are fibers (cells) that possess varying qualities that
affect the performance of the entire muscle. Some of these fibers are large and can
produce a lot of force or contract very rapidly during each of a very few maximal
contractions. If the muscle is called upon to continue to contract, these fibers
fatigue at a fast rate and cannot contribute to the force production. In contrast,
there are other muscle fibers that are smaller in diameter and cannot produce as
great a force during maximal contractions and cannot contribute to force
production during very rapid contractions. Instead, these fibers resist fatigue
during repeated contractions. Muscle size and force production during physical
tasks can be used on a comparison basis to estimate the predominance of muscle
type between individuals. The purpose of this part of lab is to estimate muscle
fiber type and determine the influence fiber type has on sport performance.
Lab Activity IIIA.
Each person in your group will perform a standing, vertical jump test near a
measured wall or with a vertical leap measurement device. Record each subject’s
jump height on the data form (round to the nearest whole inch). Calculate the
jump height corrected for body weight (net jump ht (inches) * weight (lbs) ).
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Lab Activity IIIB.
Each person in your group will perform a 10-15 second sprint on the cycle
ergometer at a tension of 1 kg (male) 0.75 kg (female). The goal is to reach the
highest rpm possible. Record the maximum revolution rate accomplished.
Lab Activity IIIC.
Each person in your group will perform a 20-yard sprint run. Time the run and
record it on the data form (round to the nearest whole second).
Lab Activity IIID.
Each person in your group will have the girth of their dominant leg measured at
the point equidistant from the anterior superior iliac spine (ASIS) and the tibial
tuberosity.
Lab Activity IIIE.
Each person in your group will perform a stair run-up test to measure power. Run
up one flight of stairs while a partner records the time. Measure the vertical
distance from the bottom to top step. Record each subject’s time on the data form
(round to the nearest half second). Calculate the power corrected for body weight
(vertical distance (feet) * weight (lbs) / time (sec)
Lab Assignment IIIA.
1) Using data from the entire class generate a correlation between each of the
following and leg girth – six correlations total.
(a) net jump height
(b) jump height corrected for body weight
(c) time for stair step
(d) power for stair step
(e) cycle rpm
(f) sprint time
2) Put your correlations in a “presentation” table.
3) Briefly describe the strength of the relationship between thigh muscle size and
each of the tasks performed.
4) Describe whether performance on the tasks could be explained by the subjects’
muscle fiber type profile.
5) Describe the kinds of sports those who performed better would be genetically
predisposed to be successful.
6) Describe where you fall on the genetic/performance spectrum we developed in
class.
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7) In which sports would this make you genetically predisposed to be successful?
8) Has that actually occurred and how or why not?
Sample Presentation table:
TABLE 1. Correlationa between performance variables and thigh girth.
Predictor Variables
Jump height (in)
Jump height corrected for body wt.
Time for stair step
Power for stair step
Cycle revolutions (rpm)
Sprint time (sec)
a
Students
(N = 28)
0.78
0.92
0.64
0.70
-0.51
0.84
Sample size for women = 10. Sample size for men = 18.
DATA FORM
LAB 4
LAB ACTIVITY IIA.
Subject:
Normal Extension
Full Flexion
Full
Hyperextension
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LAB ACTIVITY IIIA-D
Subject:
Vertical
Jump
Height (in.)
Cycle
Stair Run
Ergometer Time (sec)
Sprint
RPM’s
20 yd Sprint
Time (sec)
5
Quadriceps
Girth (in.)
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