Transcript task123x - Science and Mathematics Academy

The difference in strengthening of isometric and dynamic exercise
routines on the external rotators of the shoulder in adolescents
Lucas Spaeth
Mentored by Susan Dumler, OT Coordinator; OTR/L, CHT, CLT-UE
Introduction
Methods (continued)
Results (continued)
The Center for Disease Control states that almost twenty percent of
adults strength train more than twice a week, but experts do not agree
on which form of strength training increases muscle strength the most:
isometric or dynamic. Isometric strength training programs use static
force to train the muscle as the participant contracts muscles without
changing the overall muscle length (Hoffman, 2002). Dynamic
strength training requires the muscle to shorten and lengthen with both
concentric and eccentric contractions, improving strength by moving
joints across the full range of motion (Hoffman, 2002). The shoulder is
one of the most frequently injured joints on the human body, because it
is one of the most frequently used joints in many physical activities.
As a result, it is important to prevent injury, by strengthening all of the
muscles in the glenohumeral joint. Little is known about strength
training two muscles, the infraspinatus and the teres minor, which
perform external rotation as well as provide stabilization of the
glenohumeral joint. Few, if any, studies have explored the differences
between isometric and dynamic strength training in strengthening the
external rotators of the shoulder. The purpose of this study is to obtain
data on these differences in adolescents. Due to the popular use of
dynamic lifts during strength training, it was hypothesized that
subjects should gain more strength with a dynamic exercise.
A Manual Muscle Tester (MMT) was used to record strength gains
during the five weeks of strengthening. To ensure accurate testing
subjects were placed into a splint which kept the glenohumeral joint at
ninety degrees of abduction, and the elbow at ninety degrees of flexion
(Figure 3). Subjects were tested using the Kendall method with all
subjects lying prone on a table with their right arm in the splint and
their left arm at their side (Kendall, 1983).
All force data was recorded after five weeks for each subject. The
box plot shows a number of outliers, especially in the isometric group
of subjects. Normality graphs (not shown) were also made which
verified that the isometric group is fairly normal while the dynamic
group is slightly skewed right. Due to subject number, data choice, and
the outliers present in both exercises, a Mann-Whitney test was
performed on the data. This test gave a significance level of 0.0921 for
the null hypothesis of isometric strength gain and dynamic strength
gain being equal.
Methods
In order to compare these two
exercises, twenty four subjects
(twelve females and twelve
males) between the ages of
fourteen to eighteen were
randomly placed into two
groups. One group performed a
dynamic exercise routine
(Figure 1) and the other
Figure 1 (above): a dynamic exercise being
performed an isometric exercise performed. Subject was side-lying with the
routine (Figure 2).These
head supported.
routines were performed for
approximately five minutes
Figure 2 (left): an
isometric exercise
twice a week for five weeks.
being performed; feet
Each dynamic subject lifted
are placed shoulder
seventy-five percent of their one
width apart with the
repetition maximum which then
forearm against the
wall. The subject
determined the amount of sets
pushes on the wall
and repetitions done during the
for five seconds, ten
exercise routine.
times, for two sets.
Figure 3 (left): the strength testing
procedure for the external rotators of
the shoulder. The subject was laying
prone on a level surface with their
right arm in the splint off the table. A
force that was resisted, was applied to
the subject’s wrist. A hand was placed
on the subject’s back to ensure that the
subject only utilized the strength in
their external rotators.
Results
MMT Data, collected from February 2nd to March 8th, was
compared between the isometric and dynamic groups. The percentage
change in strength for subjects in each group, which was found by
finding the ratio of the difference in force between the initial and final
test and the initial tests, was plotted in box plots (Graph 1).
Conclusions
While it was originally hypothesized that a dynamic exercise would
strengthen more than an isometric exercise routine because of its
popularity among weight trainers, it makes sense that when the
exercises are performed by people who have not weight trained,
isometric would have a higher strength gain. This is due to the fact that
isometric exercises are primarily used with strength training during
early recovery from injury. However, this can only be said for the data
when looking at the mean and median. When the statistical results of
the Mann-Whitney test are analyzed, it can not be concluded as to
whether dynamic or isometric strength training programs cause a
greater increase in strength in a healthy adolescent population. With a
p-value of 0.0921, greater than an alpha level of 0.05, there is not
enough statistical evidence to reject the null hypothesis that isometric
and dynamic strength gains are equal. Since people will gain equal
strength from the exercises, both will help prevent shoulder injuries in
adolescent athletes. Neither exercise caused a sufficient enough
strength gain to be proven more effective. A larger subject pool and
increased time for strengthening may support differences in the two
exercises. Both exercises are viable ways to strengthen the external
rotators of the shoulder to provide stability during rigorous training.
References
Hoffman, J. (2002). Physiological Aspects of Sport Training and Performance.
Champaign, IL: Human Kinetics.
Kendall, F. (1983). Muscles, testing and function. Baltimore, MD: Williams & Wilkins.
Acknowledgements
Graph 1 (above): a box plot of the percentage of strength gained for each group. The
isometric exercise had higher percentages of strength gain than the dynamic.
Thanks to the staff at the Union Memorial Sports Medicine Center
especially Marian Mackenzie for her extensive help at the beginning of
the project. Thanks to my faculty advisor Mrs. Gabriel and all of those
who participated and helped in my study.