Journal of Orthopaedic & Sports Physical Therapy
l999;29(7)Al3-420
Resistance Properties of Thera-Band@Tubing
During Shoulder Abduction Exercise
Christopher1. Hughes, P7; PhDl
Kenneth Hurd, DP7; MS, ATC2
Allan )ones, DPP
Stephen Sprigle, P h D
Study Design: Single-group, repeated measures.
Objectives: To investigate the relationship between tubing length and tubing tension for 6
colors of Thera-Band tubing (each color representing a different level of resistance) and to
estimate the resistive shoulder toque provided during shoulder abduction exercise.
Background: Thera-Band tubing is popular for providing resistance in rehabilitation
strengthening programs. Unfortunately, it is difficult to compare use of elastic tubing with
other resistance training methods because no published data exist on how much resistance
is being provided during exercise.
Methods and Measures: Nine male and 6 female subjects (age, 25.9 3.6 years; height,
173 z 10 cm) performed shoulder abduction, using 6 colors of tubing. A strain gauge
attached at the fixed end of the tubing directly measured the tension generated during
stretch. For each color of tubing, each subject momentarily held a position at 30°, 60°, 90°,
120°, and 150" of abduction. Shoulder joint abduction, limb segment position, and tubing
length were analyzed by means of the Peak Motion Measurement System. Simple linear
regression equations predicted tubing tension from percent change in tubing length at the
joint angle positions. A 2-way (5 X 6) repeated-measuresANOVA determined the mean
differences in tubing tension across tubing colors at the shoulder abduction positions.
Results: Strong linear relationships were found for each tubing tension when referenced
according to changes in tubing length. Significant differences in tension were found for the
various colon of tubing. The resistive torque curves for each color tubing were similar to
isotonic exercise.
Conclusiom: Thera-Band tubing provides linear resistance during shoulder abduction, but
the resistive torque provided by the tubing mimics isotonic exercise. ) Orthop Sports Phys
Ther l999;29:4 13620.
+
Key Words: elastic tubing exercise, strength
Graduate School of Physical Therapy, Slippery Rock Universify Slippery Rock, Pd.
Staff physical therapist, Youngstown Orthopedic and Sports Therapy, Canfield, Ohio.
Benson Rehabilitation Services, Benson, Ariz.
Director, Center for Rehabilitation Technology, Helen Hayes Hospital, West Haverstraw, NY.
Send correspondence to Christopher Hughes, Professor, Graduate School of Physical Therapy, Slip
pry Rock Universify Slippery Rock, PA 16057. E-mail: [email protected]
I
mprovement in muscle
strength is often a desired
outcome of patient rehabilitation. To this end, therapists have a variety of training modes available. Isotonic, i s
kinetic, and isometric exercise
represent the major classifications
of strengthening exer~ise.~.'J~
Isotonic exercise requires that a segment move a constant weight
through a range of motion. Isokinetic exercise is performed whereby joint motion occurs at a preset
speed or under a controlled velocity. During isokinetic exercise, varied resistance is encountered
P
throughout the joint range of motion. Isometric exercise uses a s u b
maximal or maximal muscle effort
with no joint motion occurring.
The choice of exercise appears to
influence the amount and rate of
strength gain and the adaptations
that occur in skeletal m u ~ c l e . ~ J ~ . ~ ~
However, regardless of the choice
of exercise, the resistance must be
progressive for the most rapid
strength gains to occur." The
training method usually depends
on the patient's type of injury,
stage of recovery, and ability."
Resistance training using elastic
tubing seems to fall into a distinct
category. Unlike traditional resistance exercise methods, use of
elastic tubing relies on the tensile
'
properties of latex or other elastic polymers as a
form of resistance. The level of resistance varies according to rate and elongation of stretch of the material. The resistance properties of tubing are often
compared to the dynamics of a spring, whereby the
change in length (applied force), type of material
(modulus of elasticity), and cross-sectional area dictate the magnitude of resistance and the amount of
potential energy stored.lRSince the resistance is not
constant, elastic exercise is not formally considered
isotonic exercise. In addition, the rate of stretch may
be nonuniform, and this prohibits elastic tubing exercise from being categorized as a form of isokinetic
exercise. Despite this categorical dilemma, elastic
tubing exercise is commonly used for therapeutic exercise because of its low cost, simplicity, portability,
versatility, and nonreliance on gravity for resistance.
Elastic tubing exercise seems especially popular for
Specific protocols
shoulder rehabilitati~n.~."I~J~~~;~~
and methods have been described that advocate exclusive use of elastic bands in strengthening the rotator cuff muscles.1S21
Almost all studies investigating elastic tubing have
focused on the strength increases that one can expect when using this form of training.1J5J7.2R
Past
studies have shown elastic tubing exercise to be a
suitable method for increasing strength in the elderly, young healthy adults, and athletes. Skelton et alZ2
reported significant increases in posttest isometric
strength of the elbow flexors and knee extensors in
elderly women who underwent a 12-week training
program using isotonic or elastic tubing for resistance training. They reported 27% gains in maximum strength over the period of the study. A recent
study by Jette and colleaguesYalso showed strength
gains in communitydwelling adults, aged 60-94
years, who participated in a &month home exercise
program that exclusively used elastic bands for resistance. Mikesky et all5 showed substantial strength increases in older adults who used elastic tubing over a
12-week period. Additional studies by Brill et a l h n d
Topp et a1'4:25 also provide data supporting resistance
training benefits and carryover to function from exercise with elastic bands.
Younger subjects using tubing exercise have also
shown strength increases. Anderson et all reported
an increase of approximately 10% for the shoulder
internal rotators after 6 weeks of training. Ward et
al2%ompared free weights and Thera-Band elastic
tubing and found that both methods were equally effective in increasing external rotation strength of the
shoulder muscles after 4 weeks of training. 0'Brien17
also found strength benefits for college-aged women
who performed posterior rotator cuff exercises for 6
weeks. Furthermore, Page et all9 reported gains
when tubing was used in a "functional" or diagonal
shoulder motion to strengthen collegiate pitchers.
The researchers stated that "Many use elastic tubing
exercise as a strengthening device; however, most do
not know the extent or actual value of its resistance."19(~352)
Despite documented improvements in strength
from this type of training, few studies have detailed
the actual resistance provided by elastic bands or t u b
ing.I0 Most investigators have used a repetition limit
to decide when to progress to a higher level of resis
tance. Only the studies by 0'Brien17 and Mikesky et
all5 cite a formal method or mechanical procedure
for determining band tension as a function of elongation prior to starting a training program. Because
no data exist on how much resistance is being provided, it is difficult to compare elastic tubing exercise
with other conventional methods of training. This
makes it difficult to standardize subject effort and to
compare the training effects with other forms of exercise.
We believe a void exists in the literature. There a p
pears to be a lack of data quantifying not only the
resistance provided across the various colors (resistance levels) of tubing, but also a lack of data detailing the actual resistance provided during performance of an exercise. This information seems essential in determining the intensity of this type of training compared with other forms of resistance
exercise. Such data would assist clinicians in standardizing exercise and progression of exercise to a p
propriate levels of intensity in accordance with the
overload principle of resistance training.2.J.23.24
Furthermore, the information would assist the clinician
in helping patients progress to other forms of resistance exercise (ie, dumbbells or machines). This information could also be used to calculate the torque
provided throughout the exercise range of motion.
In a comprehensive review of skeletal muscle mechanics, Lieber and Bodine-Fowler" state that
strength must also be expressed in relation to torque
to understand the true strength requirements and effect of the exercise on the musculoskeletal system.
They further state that resistance training must include variables that relate to magnitude of force, moment arm, and angle between the moving segment
and the direction in which the resistance is acting.
Thus, not only will a particular joint movement possess a torque versus joint angle curve, otherwise
known as a strength
curve, but resistance exercise
can also generate a resistive torque curve as a function of joint position.
To rectify the lack of information concerning the
resistive properties of tubing, the objectives for our
study were to (1) determine the resistance characteristics of 6 progressive levels of Thera-Band tubing
during shoulder abduction, and (2) estimate the resistive shoulder torque provided by Thera-Band tubing during shoulder abduction exercise.
J Orthop Sports Phys Ther.Volume 29. Number 7 .July 1999
Strain Gauge Calibration Data:
Applied Force vs Measured Force
r = .9@
SEE = 2.63
0
50
100
150
200
250
Actual Force (N)
II
I
I
I
I
FIGURE 2. Strain gauge calibration data: applied versus measured force.
I
I
\
\
I
8
\
I
I
I
I
I
I
II
I
Camera #2
FIGURE 1. Diagram of camera set-up.
METHODS
Subjects
Nine men and 6 women aged 22-34 years participated in the study. All volunteers were required to
read and sign a university-approved consent form.
The criteria for inclusion in the study required s u b
jects to be able to (1) independently perform at least
150" of active shoulder abduction using their right
upper extremity, and (2) complete at least one repetition of right shoulder abduction with a 151b d u m b
bell. This weight was selected to approximate the resistance provided by the most difficult level (Silver)
of elastic tubing. Subjects were excluded if they reported a previous or current shoulder pathology or
surgery that noticeably affected normal glenohumeral rhythm of the right shoulder. Of 20 volunteers, 15
met the inclusion criteria for this study.
Instrumentation
A diagram of the set-up is shown in Figure 1. A
commercially available strain gauge (model ITC V2.0;
J Orthop Sports Phys Ther .Volume 29. Number 7 .July 1999
Innovative Research and Development Inc, Murray,
Utah) was used to record tension in the tubing during the shoulder abduction exercise. The instrument
displays a force value to the nearest 2.2 N (0.5 lb)
when a strain is induced on the load cell. We tested
the device for repeatability by recording the tension
load induced by Thera-Band elongation. Repeatability was within 2.2 N across 3 trials at each of 5 strain
levels ranging from 20% to loo%, at 20% intervals.
Strain is a normalized measure of extension and
equals the change in length divided by the original
length of the band, which was tested at a resting
length of 116.8 cm (46 in). Tests comparing the a p
plied force to the measured force displayed by the
gauge were also done. Known loads were hung on
the unit, and the force was recorded. The data demonstrated acceptable linearity, with an error range of
7% at 45 lb to 20% at 44.5 N (10 lb). The increase
in error at higher loads was attributed to the sensitivity of the digital display recording to the nearest 0.5
lb. Figure 2 shows the applied versus measured force
curve for the gauge for loads of 3.1-198.9 N (0.7 to
44.7 lb).
The strain gauge tensiometer was anchored to an
elevated wooden platform, which was constructed by
the investigators. The platform was used to limit extraneous motion of the gauge, minimize glare on the
liquid crystal display panel of the gauge, and standardize foot position for the subject (Figure 1). Each
of the 6 Thera-Band tubing colors was independently
attached to the tensiometer during testing. The other end of the tubing was attached to a revolving plastic handle that was held by the subject.
P---T*.r
Two 60-Hz AG 450 Panasonic video cameras were
used to record subject performance. One camera was
used to enlarge the digital readings on the straingauge liquid crystal display and display them on a
video monitor. The second camera was placed perpendicular to the frontal plane of the subject 15 feet
away and adjusted to capture the total area of movement of the subject. The video monitor attached to
the first camera was placed in the field of view of a
second camera, to enlarge the digital values output
from the gauge and to allow the force values to coincide with the video frames of the second camera.
Each subject wore reflective markers that attached to
standard positions on the right upper extremity, pelvis, and right lower extremity to assist in highlighting
the limb segment and to improve accuracy during
the digitization process. The Peak Performance M e
tion Measurement System was used to process the
data. The 2D data-acquisition module was used to
create a spatial model and calculate the joint position and angle data. All marker points were digitized
manually by the same investigator, to minimize error
in the digitization process.
Test Procedures
All subjects meeting the inclusion criteria were required to read and sign a university-approved informed consent form. Subjects were first required to
take part in a !%minutewarm-up consisting of active
shoulder exercises. This included pendulum and
wand exercises as well as general active stretching of
the right shoulder joint.
Subjects were dressed in shorts and a tank top, to
expose bony landmarks. Each subject's sex, height,
weight, and selected anthropomemc measures were
recorded. Anthropometric measurements included
arm length, distance from the floor to the center of
the glenohumeral joint (approximately 2 cm inferior
to the acromioclavicularjoint), and distance from
the subject's third metacarpophalangeal to the base
of the wooden platform.
During the final phase of the pretest session, bony
landmarks on the subject's right side were then located for placement of the reflective markers. The actual landmarks included (1) the estimated axis of the
glenohumeral joint 2 cm inferior to the distal end of
the acromion, (2) the medial epicondyle of the humerus, (3) the anterior midpoint of the radiocarpal
joint of the wrist, (4) the anterior-superior iliac
spine, (5) the tibia1 tubercle, and (6) the anterior
talocrural joint line. The upperextremity and trunk
markers were used to calculate the shoulder abduction angle. The glenohumeral joint marker formed
the apex and the medial epicondyle of the humerus,
and anterior-superior iliac spine markers represented
the proximal and distal segment endpoints (Figure 3).
416
FIGURE 3. Variables used in determining shoulder torque.
The test session began with the subject standing in
anatomical position on the platform. Using the right
hand, the subject pronated the wrist and gripped the
handle attached to the "free" end of the tubing.
The "anchored" end was attached to the strain
gauge device at a height that was level with the base
of the platform. The "resting" or original band
length was cut according to the distance measured
from the subject's third metacarpophalangealjoint to
the attachment point of the gauge.
Tubing colors were randomized prior to testing.
For each of the 6 tubing colors, 5 repetitions of
shoulder abduction (0-150') were performed with
the subject momentarily holding arm positions at angles of 30°, 60°, 90°, 120°, and 150".Joint angles were
approximated by use of angles created with lines of
tape on a cardboard backdrop. The backdrop was
used only to assist with correlation of a group of
frames close to the intended joint range, to minimize
the time required during the digitization process.
Each subject completed a total of 30 repetitions for
all band colors. Subjects were instructed to slowly
control the stretch of the band, to decrease the effect of acceleration, by momentarily holding at the
specific joint angle positions under investigation.
Randomization of each color served to control for
the effects of fatigue, and a rest period of 2 minutes
was provided after each tubing color was used.
The processed data fkom the digitization process
generated the following data: (1) segment length
from the glenohumeral joint center to the third metacarpophalangealjoint, (2) tubing length at each of
the 5 joint positions, (3) shoulder joint angle at the
5 joint positions, and (4) the angle created by the
long axis of the tubing and the longitudinal axis of
the right upper extremity. This angle was termed the
J Onhop Sports Phys Ther .Volume 29 Number 7-July 1999
TABLE 1. Regression equations for each color of Thera-Band tubing.
Band
color
Yellow
Red
Green
Blue
Black
Silver
r
Z
.86
.97
.99
.98
.99
.99
.74
.94
.98
.96
.98
.98
Regression equation*
SEE)
= .03 (x) + 3.07
1.07
1.54
1.67
1.97
1.94
2.29
Y'
Y'
Y'
Y'
Y'
Y'
= .12 (x) + 6.07
= .18 (x) + 8.42
= .20 (x) + 9.92
= .23 (x) + 10.38
= .35 (x) + 13.19
-Yellow
+ Red
* Green
* Blue
* Black
* Silver
Y', predicted tubing tension (N);x, percent change in tubing length.
t SEE, standard error of the estimate.
% Band Length Change
band-twnn angle. Force values were also obtained
from the strain gauge at the intended joint positions
during digitization. We calculated torque values for
each band color by using the information and equation shown in Figure 3. To allow comparison of the
resistive torque curves with traditional isotonic exercise, we used the same values to compute resistive
torque values across the same joint angles as would
be used if the subjects attempted the movement with
a 22.25 N load (5 lb) and a 44.5 N load (10 lb).
0% = Startlng Length
FIGURE 5. Tubing tension in relation to percent length change of tubing
for each band color. Standard deviations (SDs) are shown in Table 4.
RESULTS
The results of the linear regression analysis are
shown in Table 1. Figure 4 shows the tension length
curve for the averaged vials of each tubing color
across the 5 joint positions. Tension values for all
tubing
colors ranged from a minimum of 3.3 N for
Statistical Analysis
the yellow band at the 30" range to a maximum of
Simple linear regression was used to predict tubing 70.1 N for the silver tubing at the 150" range. Stantension from percent of tubing length for each color dard deviations for tension values ranged from a
minimum of 0.89 N for the yellow tubing to a maxiof tubing. A 2-way (angle X color) repeated meamum of 3.0 N for the silver tubing. Tension changes
sures ANOVA was performed to determine whether
expressed as a function of percent tubing length are
mean differences in tubing tension occurred among
tubing colors at SO0, 60°, 90°, 120°, and 150" of shoul- shown in Figure 5. Tubing length changes expressed
der abduction. If significance was found, then Tukey in relation to the original or "resting" length ranged
from a minimum of 18% stretch from resting length
post hoc testing was done to specify significant pairat the low angle of abduction to 159% at the exwise differences among the factors. A between-sub
treme range of shoulder motion. Resistive torque valjects comparison was also done to determine whether tension that developed in the tubing was indepen- ues were minimal at the extreme ranges but all
torque values were maximal at 90" of shoulder abdent of subjects. Statistical significance for all tests
duction (Figure 6). This position coincided with a
was defined as P < .05.
band-tearm angle of approximately 60" across the
-Yellow
-Yellow
+Red
+Red
* Green
* Green
+Blue
+Blue
*Black
* Black
*Silver
*Silver
+5 #
+lo#
20
40
60
80
100
120
140
160
Shoulder Angle (degrees)
FIGURE 4. Tubing tension versus joint angle for each tubing color.
Standard deviations (SDs) are shown in Table 3.
J Onhop Sports Phys Ther-Volume 29. Number 7 .July 1999
Joint Angle (degrees)
FIGURE 6. Resistive torque curves for each color of tubing. Standard deviations (SDs) are shown in Table 5.
TABLE 2. Two-factor ANOVA (tubing color X angle) for tension developed during shoulder abduction using Thera-Band elastic tubing.
Source
Angle
43806.47
4
10951.62
4136.47
.OOO*
Error
Tubing Color
Error
Angle X Color
Error
Significant at P < .05.
tubing trials. Standard deviation values for data
shown in Figures 4-6 can be found in corresponding
Tables 3-5. The analysis of variance can be found in
Table 2. Significant main effects and a significant interaction were found for the test conditions. No significant difference was found for the between-sub
jects comparison (I;,.,, = 4.17, P = .O6). Tukey's post
hoc analysis showed significant mean tension differences at each angle for all colon, except comparison
of blue and black tube tension at 30' (Figure 4).
DISCUSSION
The results of this study shed light on the resistive
properties provided by elastic tubing during exercise.
The strong linear relationship between tubing tension and tubing excursion (percent length change)
seems logical given the material properties of the
band. However, it is interesting to note that the
grade of resistance levels across tubing colors is not
standard.
Figure 4 shows fairly similar resistance for green,
blue, and black tubing but fairly discrepant slopes
for yellow, red, and silver. The mechanical strains are
unique, are a function of the thickness of material
used for each color tubing, and may also have been
influenced by the stretch rate during the trials. Our
TABLE 3. Mean (SD) tension (in newtons) for each joint angle and tubing
color.
Band
color
Yellow
Red
Green
Blue
Black
Silver
Tension at mean
shoulder angle
300
60"
900
1200
1500
3.3
(1.1
7.1
(1.5)
10.4
(1.8)
12.2
(0.38)
12.5
(2.O)
17.5
(3.O)
5.5
(1.1)
13.5
(1.6)
19.9
(2.0)
22.2
(1.5)
24.8
(1.7)
34.1
(2.1)
6.7
(0.0)
18.3
(1.7)
26.7
(1.71
30.0
(1.4)
33.8
(1.5)
49.4
(2.7)
7.1
(0.9)
22.2
(1.5)
33.4
(1.9)
37.5
(1.7)
41.4
(1.8)
60.9
(2.0)
8.6
(1.1)
24.9
(1.5)
36.9
(1.4)
41.8
(2.5)
46.3
(2.4)
70.1
(2.4)
subjects were only instructed to slowly control the
stretch of the band and then decrease the effect of
acceleration by momentarily holding at the specific
joint angle positions under investigation.
Probably the most informative data from the study
are shown by the torque angle curves in Figure 6.
Despite a progressive increase in tension response by
the band, the angle of the band to the arm plays a
significant role in the resistive torque applied to the
shoulder. This observation needs to be studied closely. When one compares the torque data from tubing
with isotonic loads of 5 and 10 lb included in Figure
6, it becomes clear that the resistive patterns are
strikingly similar. The blue tubing appears to most
closely resemble the 51b load, whereas the silver t u b
ing resembles very closely the 10-lb load. The data
indicate that, when patients use the silver tubing,
they closely approximate the torque required when
using a 10-lb weight, whereas the blue tubing replicates the 51b load. Thus, if a therapist would like a
patient to progress from tubing to isotonic exercise,
a load greater than 10 lb may be needed to stimulate
an overload response by the patient's muscle. These
results should be verified in future studies.
Kisner and Colby1I imply that a primary disadvantage of elastic resistance exercisers is related to the
linear resistance provided. This form of resistance
TABLE 4. Mean (SD) tubing tension (in newtons) for percentage length
change of tubing, for each band color.
Band
color
Yellow
Red
Green
Blue
Black
Silver
Mean tension for percentage length change
19
58
104
140
160
3.3
(1.1)
7.1
(1.5)
10.4
(1.8)
12.2
(0.38)
12.5
(2.0)
17.5
(3.0)
5.5
(1.1
13.5
(1.6)
19.9
(2.0)
22.2
(1.5)
24.8
(1.7)
34.1
(2.1)
6.7
(0.0)
18.3
(1.7)
26.7
(1.7)
30.0
(1.4)
33.8
(1.5)
49.4
(2.7)
7.1
(0.9)
22.2
(1.5)
33.4
(1.9)
37.5
(1.7)
41.4
(1.8)
60.9
(2.0)
8.6
(1.1)
24.9
(1.5)
36.9
(1.4)
41.8
(2.5)
46.3
(2.4)
70.1
(2.4)
J Orthop Sporu Phys Ther *Volume 29 Number 7 *July 1999
TABLE 5. Mean (SD) torque measurements (in newton-meters) for each
color of Thera-Band tubing.
Band
color
Yellow
Red
Green
Blue
Black
Silver
5 Ib
10 lb
Mean toque at shoulder angle
300
60"
90"
120"
1500
2.2
(0.9)
4.9
(0.9)
6.3
(1.2)
7.3
(1.1
4.6
(0.3)
9.6
(1.3)
16.3
(1.7)
16.0
(1.4)
7.9
(1.4)
11.2
(2.4)
8.13
(0.8)
18
(1.7)
22.4
(2.6)
13.2
(1.O)
4.7
(0.3)
12.9
(1.4)
17.3
(1.8)
18.9
(1.8)
20.3
(1.8)
27.5
(3.1)
19.2
(1.1)
3.7
(0.6)
10.5
(1.2)
13.3
(2.O)
16.1
(2.3)
17.9
(2.6)
25.5
(2.8)
13.35
(1.1)
1.6
(.6)
6.8
(1.2)
9.4
(2.2)
8.4
(2.5)
12.8
(2.8)
15.9
(3.3)
8.75
(1.3)
16.1
(1.6)
26.1
(2.0)
30.0
(2.3)
26.4
(2.3)
17.3
(2.6)
makes it difficult for the patient to finish the end of
range, because the muscles are weaker at the point
where the resistance is greatest.ls If one considers resistance to joint rotation, then the resistive torque
data from our study are in disagreement with this observation. The torque seems to follow an ascendingdescending pattern, with the greatest torque occurring near 90" of abduction. The 90" of shoulder abduction includes all interactions among the musculoskeletal system: muscle length, joint position, varying
resistance, and joint angle, as well as the line of resis
tance. These factors play a major role in defining an
exercise pattern and the amount of effort required
and therefore must be evaluated for each prescribed
exercise.'"rne
of these factors appear to influence
the linear resistance provided by the tubing. Even
though the resistance increases as joint angle increases, the band-to-arm angle and shoulder abduction
angle offset the linearity and vary the torque in a
manner that represents one of the most commonly
seen strength curves for the majority of muscle
groups in the body.'2
In a review of literature, Kulig et all2 showed that
the strength curve of shoulder abduction was a descending pattern, with greatest abduction strength
occurring early in the range of motion. This is where
the resistance created by arm length has the least impact on resistive torque at the shoulder, and muscle
mechanics may be more favorable, consequently allowing for increased force.
We acknowledge several limitations in the study.
The first is our use of a commercial strain gauge.
The gauge was able to record only to the nearest 0.5
pounds across all tubing colors. This influenced the
accuracy with which we could record some of the
smaller tension values, especially in tests of the yelJ Orthop Sports Phys Ther -Volume 29. Number 7 .July 1999
low tubing. Another limitation is the lack of control
for limb speed. Even though subjects were told to
perform slow, controlled movements, it is possible
that the subjects accelerated the limb, placing an additional inertial strain on the gauge and inflating the
recorded values. However, our finding of statistically
nonsignificant differences between subjects indicates
that constant tubing tension can be maintained if exercise movements are performed slowly. In addition,
the angle measures were approximated from the videotape and digitizing process. Our indirect assessment of the range of motion was limited by our ability to coincide the video frame number for joint angle measurement with the strain gauge value d i s
played in the frame field. In some analyses this value
was equal across a number of frames, and when coupled with the 0.51b resolution of the gauge, this may
have skewed our joint angle positions and inevitably
influenced the force values. This is why some of our
angle values approximated the intended joint positions under investigation. In addition. we did not use
a comprehensive model for calculating the resistive
torque at the shoulder. To calculate the torque
curves for the isotonic loads, we used the average anthropometric segment lengths obtained from our
sample and did not include individual estimated
limb weights. Furthermore, our not performing electromyographic analysis limits our discussion to loading at the glenohumeral joint and prevents fruitful
discussion regarding the role of individual shoulder
muscles in performing resistance exercise with elastic
tubing. However, a recent study by Hintermeister et
al" indicated that electromyographic levels in select
shoulder muscles were of adequate intensity when
elastic cords were used as resistance.
Despite these limitations, we feel that the results
shed light on the effects of elastic exercise on tension development. We recommend further investigations to determine strain values with accelerated exercise movements, especially with eccentric training
loads and different joint movements, and also investigations using electromyographic analysis to determine load sharing among muscles that act as prime
movers.
CONCLUSION
Our results support the linear response of TheraBand tubing in providing resistance during shoulder
exercise. However, the resistive torque pattern provided by various levels of elastic tubing appears to be
similar to that provided by traditional isotonic exercise for shoulder abduction. The minimum and maximum resistance for each tubing color were identified and can be extrapolated to other exercises that
result in similar length changes. Additional research
on the biomechanics of elastic band training needs
to be performed to more completely delineate the
419
advantages and disadvantages o f using elastic bands
as a method o f resistance exercise for patients involved in a rehabilitation program.
15.
ACKNOWLEDGMENTS
T h e authors thank the Hygenic Corporation,
ron, Ohio, f o r supplying the Thera-Band.
14.
Ak-
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J Orthop Sports Phys Ther .Volume 29. Number 7 .July 1999