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Journal of Orthopaedic & Sports Physical Therapyl999;29 7)Al3-420

Resistance Properties of Thera-Band@TubingDuring Shoulder Abduction ExerciseChristopher1. Hughes, P7; Ph DlKenneth Hurd, DP7; MS, ATC2Allan )ones, DPPStephen Sprigle, Ph D

Study Design: Single-group, repeated measures.Objectives: To investigate the relationship between tubing length and tubing tension for 6colors of Thera-Band tubing (each color representing a different level of resistance) and toestimate the resistive shoulder toq ue provided during shoulder abduction exercise.Background: Thera-Band tubing is popular for provid ing resistance in rehabilitationstrengthening programs. Unfortunately, it is difficult to compare use of elastic tubing withother resistance training methods because no published data exist on how much resistanceis 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 gaugeattached at the fixed end of the tubing directly measured the tension generated duringstretch. For each colo r of tubing, each subject momentarily held a position at 30 60 90120 and 150"of abduction. Shoulder joint abduction, limb segment position, and tubinglength were analyzed by means of the Peak Motion Measurement System. Simple linearregression equations predicted tubing tension from percent change in tubing length at thejoin t angle positions. A 2-way (5 X 6) repeated-measures ANOVA determined the meandifferences in tubing tension across tubing colors at the shoulder abduction positions.Results: Strong linear relationships were found for each tubing tension when referencedaccording to changes in tubing length. Significant differences in tension were found for thevarious colon of tubing. The resistive torque curves for each colo r tubing were similar toisotonic exercise.Conclusiom: Thera-Band tubing provides linear resistance during shoulder abduction, butthe resistive torque provided by the tubing mimics isotonic exercise. ) Orthop Sports PhysTher 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, Slippry Rock Universify Slippery Rock, PA 16057. E-mail: [email protected]

I provement in musclestrength is often a desiredoutcome of patient rehabil-itation. To this end, thera-pists have a variety of train-ing modes available. Isotonic, i skinetic, and isometric exerciserepresent the major classificationsof strengthening exer~is e.~ .'J ~so-tonic exercise requires that a seg-ment move a constant weightthrough a range of motion. Isoki-netic exercise is performed where-by joint motion occurs at a preset 'speed or under a controlled veloc-ity. During isokinetic exercise, var-ied resistance is encountered Pthroughout the joint range of mo-tion. Isometric exercise uses a su bmaximal or maximal muscle effortwith no joint motion occurring.The choice of exercise appears toinfluence the amount and rate ofstrength gain and the adaptationsthat occur in skeletal m u ~ c l e . ~ J ~ . ~ ~However, regardless of the choiceof exercise, the resistance must beprogressive for the most rapidstrength gains to occur." Thetraining method usually dependson the patient's type of injury,stage of recovery, and ability."

Resistance training using elastictubing seems to fall into a distinctcategory. Unlike traditional resis-tance exercise methods, use ofelastic tubing relies on the tensile


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properties of latex or other elastic polymers as aform of resistance. The level of resistance varies ac-cording to rate and elongation of stretch of the ma-terial. The resistance properties of tubing are oftencompared to the dynamics of a spring, whereby thechange in length (applied force), type of material(modulus of elasticity), and cross-sectional area dic-tate the magnitude of resistance and the amount ofpotential energy stored.lRSince the resistance is notconstant, elastic exercise is not formally consideredisotonic exercise. In addition, the rate of stretch maybe nonuniform, and this prohibits elastic tubing ex-ercise from being categorized as a form of isokineticexercise. Despite this categorical dilemma, elastictubing exercise is commonly used for therapeutic ex-ercise because of its low cost, simplicity, portability,versatility, and nonreliance on gravity for resistance.Elastic tubing exercise seems especially popular forshoulder rehabilitati~n.~."I~J~~~;~~pecific protocolsand methods have been described that advocate ex-clusive use of elastic bands in strengthening the rota-tor cuff muscles.1S21

Almost all studies investigating elastic tubing havefocused on the strength increases that one can ex-pect when using this form of training.1J5J7.2Raststudies have shown elastic tubing exercise to be asuitable method for increasing strength in the elder-ly, young healthy adults, and athletes. Skelton et alZ2reported significant increases in posttest isometricstrength of the elbow flexors and knee extensors inelderly women who underwent a 12-week trainingprogram using isotonic or elastic tubing for resis-tance training. They reported 27% gains in maxi-mum strength over the period of the study. A recentstudy by Jette and colleaguesY lso showed strengthgains in communitydwelling adults, aged 60-94years, who participated in a &month home exerciseprogram that exclusively used elastic bands for resis-tance. Mikesky e t all5 showed substantial strength in-creases in older adults who used elastic tubing over a12-week period. Additional studies by Brill et a l h n dTopp et a1'4:25 also provide data supporting resistancetraining benefits and carryover to function from ex-ercise with elastic bands.

Younger subjects using tubing exercise have alsoshown strength increases. Anderson et all reportedan increase of approximately 10% for the shoulderinternal rotators after 6 weeks of training. Ward etal2%ompared free weights and Thera-Band elastictubing and found that both methods were equally ef-fective in increasing external rotation strength of theshoulder muscles after 4 weeks of training. 0'Brien17also found strength benefits for college-aged womenwho performed posterior rotator cuff exercises for 6weeks. Furthermore, Page et all9 reported gainswhen tubing was used in a "functional" or diagonalshoulder motion to strengthen collegiate pitchers.The researchers stated that "Many use elastic tubing

exercise as a strengthening device; however, most donot know the extent or actual value of its resis-tance."19(~352)

Despite documented improvements in strengthfrom this type of training, few studies have detailedthe actual resistance provided by elastic bands or t u bing.I0 Most investigators have used a repetition limitto decide when to progress to a higher level of resistance. Only the studies by 0'Brien17 and Mikesky etall5 cite a formal method or mechanical procedurefor determining band tension as a function of elon-gation prior to starting a training program. Becauseno data exist on how much resistance is being pro-vided, it is difficult to compare elastic tubing exercisewith other conventional methods of training. Thismakes it difficult to standardize subject effort and tocompare the training effects with other forms of ex-ercise.

We believe a void exists in the literature. There a ppears to be a lack of data quantifying not only theresistance provided across the various colors (resis-tance levels) of tubing, but also a lack of data detail-ing the actual resistance provided during perfor-mance of an exercise. This information seems essen-tial in determining the intensity of this type of train-ing compared with other forms of resistanceexercise. Such data would assist clinicians in stan-dardizing exercise and progression of exercise to a ppropriate levels of intensity in accordance with theoverload principle of resistance training.2.J.23.24ur-thermore, the information would assist the clinicianin helping patients progress to other forms of resis-tance exercise (ie, dumbbells or machines). This in-formation could also be used to calculate the torqueprovided throughout the exercise range of motion.In a comprehensive review of skeletal muscle me-chanics, Lieber and Bodine-Fowler" state thatstrength must also be expressed in relation to torqueto understand the true strength requirements and ef-fect of the exercise on the musculoskeletal system.They further state that resistance training must in-clude variables that relate to magnitude of force, mo-ment arm, and angle between the moving segmentand the direction in which the resistance is acting.Thus, not only will a particular joint movement pos-sess a torque versus joint angle curve, otherwiseknown as a strength curve, but resistance exercise-can also generate a resistive torque curve as a func-tion of joint position.

To rectify the lack of information concerning theresistive properties of tubing, the objectives for ourstudy were to (1) determine the resistance character-istics of 6 progressive levels of Thera-Band tubingduring shoulder abduction, and (2) estimate the re-sistive shoulder torque provided by Thera-Band tub-ing during shoulder abduction exercise.

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III

II

IIII I\ I

\ II I8 I\ I

Camera #2

FIGURE 1. Diagram of camera set-up.

METHODSSubjects

Nine men and 6 women aged 22-34 years partici-pated in the study. All volunteers were required toread and sign a university-approved consent form.The criteria for inclusion in the study required s u bjects to be able to (1) independently perform at least150" of active shoulder abduction using their rightupper extremity, and (2) complete at least one repe-tition of right shoulder abduction with a 151b dum bbell. This weight was selected to approximate the re-sistance provided by the most difficult level (Silver)of elastic tubing. Subjects were excluded if they re-ported a previous or current shoulder pathology orsurgery that noticeably affected normal glenohumer-al rhythm of the right shoulder. Of 20 volunteers, 15met the inclusion criteria for this study.InstrumentationA diagram of the set-up is shown in Figure 1.A

commercially available strain gauge (model ITC V2.0;

Strain Gauge Calibration Data:Applied Force vs Measured Force

r = .9@SEE = 2.63

0 50 100 150 200 250Actual Force (N)

FIGURE 2. Strain gauge calibration data: applied versus measured force.

Innovative Research and Development Inc, Murray,Utah) was used to record tension in the tubing dur-ing the shoulder abduction exercise. The instrumentdisplays a force value to the nearest 2.2 N (0.5 lb)when a strain is induced on the load cell. We testedthe device for repeatability by recording the tensionload induced by Thera-Band elongation. Repeatabil-ity was within 2.2 N across 3 trials at each of 5 strainlevels ranging from 20% to loo%, at 20% intervals.Strain is a normalized measure of extension andequals the change in length divided by the originallength of the band, which was tested at a restinglength of 116.8 cm (46 in) . Tests comparing the a p P - - - Tplied force to the measured force displayed by thegauge were also done. Known loads were hung onthe unit, and the force was recorded. The data dem-onstrated acceptable linearity, with an erro r range of7% at 45 lb to 20% at 44.5 N (10 lb). The increasein error at higher loads was attributed to the sensitiv-ity of the digital display recording to the nearest 0.5lb. Figure 2 shows the applied versus measured forcecurve for the gauge for loads of 3.1-198.9 N (0.7 to44.7 lb).

The strain gauge tensiometer was anchored to anelevated wooden platform, which was constructed bythe investigators. The platform was used to limit ex-traneous motion of the gauge, minimize glare on theliquid crystal display panel of the gauge, and stan-dardize foot position for the subject (Figure 1). Eachof the 6 Thera-Band tubing colors was independentlyattached to the tensiometer during testing. The oth-er end of the tubing was attached to a revolving plas-tic handle that was held by the subject.

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Two 60-Hz AG 450 Panasonic video cameras wereused to record subject performance. One camera wasused to enlarge the digital readings on the strain-gauge liquid crystal display and display them on avideo monitor. The second camera was placed per-pendicular to the frontal plane of the subject 15 feetaway and adjusted to capture the total area of move-ment of the subject. The video monitor attached tothe first camera was placed in the field of view of asecond camera, to enlarge the digital values outputfrom the gauge and to allow the force values to coin-cide with the video frames of the second camera.Each subject wore reflective markers that attached tostandard positions on the right upper extremity, pel-vis, and right lower extremity to assist in highlightingthe limb segment and to improve accuracy duringthe digitization process. The Peak Performance M etion Measurement Systemwas used to process thedata. The 2D data-acquisition module was used tocreate a spatial model and calculate the joint posi-tion and angle data. All marker points were digitizedmanually by the same investigator, to minimize errorin the digitization process.Test Procedures

All subjects meeting the inclusion criteria were re-quired to read and sign a university-approved in-formed consent form. Subjects were first required totake part in a !%minutewarm-up consisting of activeshoulder exercises. This included pendulum andwand exercises as well as general active stretching ofthe right shoulder joint.

Subjects were dressed in shorts and a tank top, toexpose bony landmarks. Each subject's sex, height,weight, and selected anthropomemc measures wererecorded. Anthropometric measurements includedarm length, distance from the floor to the center ofthe glenohumeral joint (approximately 2 cm inferiorto the acromioclavicular oint) , and distance fromthe subject's third metacarpophalangeal to the baseof the wooden platform.

During the final phase of the pretest session, bonylandmarks on the subject's right side were then locat-ed for placement of the reflective markers. The actu-al landmarks included (1) the estimated axis of theglenohumeral joint 2 cm inferior to the distal end ofthe acromion, (2) the medial epicondyle of the hu-merus, (3) the anterior midpoint of the radiocarpaljoint of the wrist, (4) the anterior-superior iliacspine, (5) the tibia1 tubercle, and (6) the anteriortalocrural joint line. The upperextremity and trunkmarkers were used to calculate the shoulder abduc-tion angle. The glenohumeral joint marker formedthe apex and the medial epicondyle of the humerus,and anterior-superior iliac spine markers representedthe proximal and distal segment endpoints (Fig-ure 3).

FIGURE 3. Variables used in determining shoulder torque.

The test session began with the subject standing inanatomical position on the platform. Using the righthand, the subject pronated the wrist and gripped thehandle attached to the "free" end of the tubing.The "anchored" end was attached to the straingauge device at a height that was level with the baseof the platform. The "resting" or original bandlength was cut according to the distance measuredfrom the subject's third metacarpophalangeal oint tothe attachment point of the gauge.

Tubing colors were randomized prior to testing.For each of the 6 tubing colors, 5 repetitions ofshoulder abduction (0-150') were performed withthe subject momentarily holding arm positions at an-gles of 30, 60, 90, 120, and 150". Joint angles wereapproximated by use of angles created with lines oftape on a cardboard backdrop. The backdrop wasused only to assist with correlation of a group offrames close to the intended joint range, to minimizethe time required during the digitization process.Each subject completed a total of 30 repetitions forall band colors. Subjects were instructed to slowlycontrol the stretch of the band, to decrease the ef-fect of acceleration, by momentarily holding at thespecific joint angle positions under investigation.Randomization of each color served to control forthe effects of fatigue, and a rest period of 2 minuteswas provided after each tubing color was used.

The processed data fkom the digitization processgenerated the following data: (1) segment lengthfrom the glenohumeral joint center to the third me-tacarpophalangeal oint, (2) tubing length at each ofthe 5 joint positions, (3) shoulder joint angle at the5 joint positions, and (4) the angle created by thelong axis of the tubing and the longitudinal axis ofthe right upper extremity. This angle was termed the

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TABLE 1. Regression equations for each color of Thera-Band tubing.Bandcolor r Z Regressionequation* SEE)

Yellow .86 .74 Y' = .03 (x) + 3.07 1.07Red .97 .94 Y' = .12 (x) + 6.07 1.54Green .99 .98 Y' = .18 (x) + 8.42 1.67Blue .98 .96 Y' = .20 (x) + 9.92 1.97Black .99 .98 Y' = .23 (x) + 10.38 1.94Silver .99 .98 Y' = .35 (x) + 13.19 2.29Y', predicted tubing tension (N);x, percent change in tubing length.

t SEE, standard error of the estimate.

band-twnn angle.Force values were also obtainedfrom the strain gauge at the intended joint positionsduring digitization. We calculated torque values foreach band color by using the information and equa-tion shown in Figure 3. To allow comparison of theresistive torque curves with traditional isotonic exer-cise, we used the same values to compute resistivetorque values across the same joint angles aswouldbe used if the subjects attempted the movement witha 22.25 N load (5 lb) and a 44.5 N load (10 lb).

StatisticalAnalysisSimple linear regression was used to predict tubing

tension from percent of tubing length for each colorof tubing. A 2-way (angle X color) repeated mea-sures ANOVA was performed to determine whethermean differences in tubing tension occurred amongtubing colors at SO0, 60 90 120 and 150" of shoul-der abduction. If significancewas found, then Tukeypost hoc testing was done to specify significant pair-wise differences among the factors. A between-subjects comparison was also done to determine wheth-er tension that developed in the tubing was indepen-dent of subjects. Statistical significance for all testswas defined as P < .05.

20 40 60 80 100 120 140 160Shoulder Angle (degrees)

-Yellow+Red*Green*Blue*Black* ilver

%Band Length Change0% = Startlng LengthFIGURE 5. Tubing tension in relation to percent length change of tubingfor each band color. Standard deviations (SDs) are shown in Table 4.

RESULTSThe results of the linear regression analysis are

shown in Table 1. Figure 4 shows the tension lengthcurve for the averaged vials of each tubing coloracross the 5 joint positions. Tension values for alltubing colors ranged from a minimum of 3.3 N forthe yellow band at the 30" range to a maximum of70.1 N for the silver tubing at the 150" range. Stan-dard deviations for tension values ranged from aminimum of 0.89 N for the yellow tubing to a maxi-mum of 3.0 N for the silver tubing. Tension changesexpressed as a function of percent tubing length areshown in Figure 5. Tubing length changes expressedin relation to the original or "resting" length rangedfrom a minimum of 18% stretch from resting lengthat the low angle of abduction to 159% at the ex-treme range of shoulder motion. Resistive torque val-ues were minimal at the extreme ranges but alltorque values were maximal at 90" of shoulder ab-duction (Figure 6). This position coincided with aband-tearm angle of approximately 60" across the

-Yellow+ R e d*Green+Blue*Black*Silver

FIGURE 4. Tubing tension versus joint angle for each tubing color.Standard deviations (SDs) are shown in Table 3.

-Yellow+R ed* reen+Blue*Black*Silver+5 #+ l o #

Joint Angle (degrees)FIGURE 6. Resistive torque curves for each color of tubing. Standard de-viations (SDs) are shown in Table 5.

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TABLE 2. Two-factor ANOVA (tubing co lor X angle) for tension developed during shoulder abduction using Thera-Band elastic tubing.Source

Angle 43806.47 4 10951.62 41 36.47 .OOO*ErrorTubing ColorErrorAngle X ColorErrorSignificant at P < .05.tubing trials. Standard deviation values for datashown in Figures 4-6 can be found in correspondingTables 3-5. The analysis of variance can be found inTable 2. Significant main effects and a significant in-teraction were found for the test conditions. No sig-nificant difference was found for the between-subjects comparison (I;,.,, = 4.17, P = .O6). Tukey's posthoc analysis showed significant mean tension differ-ences at each angle for all colon , except comparisonof blue and black tube tension at 30' (Figure 4).DISCUSSION

The results of this study shed light on the resistiveproperties provided by elastic tubing during exercise.The strong linear relationship between tubing ten-sion and tubing excursion (percent length change)seems logical given the material properties of theband. However, it is interesting to note that thegrade of resistance levels across tubing colors is notstandard.

Figure 4 shows fairly similar resistance for green,blue, and black tubing but fairly discrepant slopesfor yellow, red, and silver. The mechanical strains areunique, are a function of the thickness of materialused for each color tubing, and may also have beeninfluenced by the stretch rate during the trials. OurTABLE 3. Mean (SD) tension (in newtons) for each joint angle and tubingcolor.

Tension at meanBand shoulder anglecolor 300 60" 900 1200 1500

subjects were only instructed to slowly control thestretch of the band and then decrease the effect ofacceleration by momentarily holding a t the specificjoint angle positions under investigation.

Probably the most informative data from the studyare shown by the torque angle curves in Figure 6.Despite a progressive increase in tension response bythe band, the angle of the band to the arm plays asignificant role in the resistive torque applied to theshoulder. This observation needs to be studied close-ly. When one compares the torque data from tubingwith isotonic loads of 5 and 10 lb included in Figure6, it becomes clear that the resistive patterns arestrikingly similar. The blue tubing appears to mostclosely resemble the 51b load, whereas the silver t u bing resembles very closely the 10-lb load. The dataindicate that, when patients use the silver tubing,they closely approximate the torque required whenusing a 10-lb weight, whereas the blue tubing repli-cates the 51b load. Thus, if a therapist would like apatient to progress from tubing to isotonic exercise,a load greater than 10 lb may be needed to stimulatean overload response by the patient's muscle. Theseresults should be verified in future studies.

Kisner and Colby1I imply that a primary disadvan-tage of elastic resistance exercisers is related to thelinear resistance provided. This form of resistance

TABLE 4. Mean (SD) tub ing tension (in newtons) for percentage lengthchange of tubing, for each band color.Band Mean tension for percentage length changecolor 19 58 104 140 160

Yellow 3.3 5.5 6.7 7.1 8.6(1.1 (1.1) (0.0) (0.9) (1.1)Red 7.1 13.5 18.3 22.2 24.9(1.5) (1.6) (1.7) (1.5) (1.5)Green 10.4 19.9 26.7 33.4 36.9(1.8) (2.0) (1.71 (1.9) (1.4)Blue 12.2 22.2 30.0 37.5 41.8(0.38) (1.5) (1.4) (1.7) (2.5)Black 12.5 24.8 33.8 41.4 46.3(2 O) (1.7) (1.5) (1.8) (2.4)Silver 17.5 34.1 49.4 60.9 70.1(3 .O) (2.1) (2.7) (2.0) (2.4)

Yellow 3.3 5.5 6.7 7.1 8.6(1.1) (1.1 (0.0) (0.9) (1.1)Red 7.1 13.5 18.3 22.2 24.9(1.5) (1.6) (1.7) (1 5) (1.5)Green 10.4 19.9 26.7 33.4 36.9(1.8) (2.0) (1.7) (1.9) (1.4)Blue 12.2 22.2 30.0 37.5 41.8(0.38) (1.5) (1.4) (1.7) (2.5)Black 12.5 24.8 33.8 41.4 46.3(2.0) (1.7) (1.5) (1.8) (2.4)Silver 17.5 34.1 49.4 60.9 70.1(3.0) (2.1) (2.7) (2.0) (2.4)

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TABLE 5. Mean (SD) torque measurements (in newton-meters) for eachcolor of Thera-Band tubing.Band Mean toque at shoulder anglecolor 300 60" 90" 120" 1500

Yellow 2.2 4.6 4.7 3.7 1.6(0.9) (0.3) (0.3) (0.6) (.6)Red 4.9 9.6 12.9 10.5 6.8(0.9) (1.3) (1.4) (1 2) (1.2)Green 6.3 16.3 17.3 13.3 9.4(1.2) (1.7) (1.8) (2 O) (2.2)Blue 7.3 16.0 18.9 16.1 8.4(1.1 (1.4) (1.8) (2.3) (2.5)Black 7.9 18 20.3 17.9 12.8(1.4) (1.7) (1.8) (2.6) (2.8)Silver 11.2 22.4 27.5 25.5 15.9(2.4) (2.6) (3.1) (2.8) (3.3)5 Ib 8.13 13.2 19.2 13.35 8.75(0.8) (1O) (1.1) (1.1) (1.3)

10 lb 16.1 26.1 30.0 26.4 17.3(1.6) (2.0) (2.3) (2.3) (2.6)

makes it difficult for the patient to finish the end ofrange, because the muscles are weaker at the pointwhere the resistance is greatest.ls If one considers re-sistance to joint rotation, then the resistive torquedata from our study are in disagreement with this ob-servation. The torque seems to follow an ascending-descending pattern, with the greatest torque occur-ring near 90" of abduction. The 90"of shoulder ab-duction includes all interactions among the musculo-skeletal system: muscle length, joint position, varyingresistance, and joint angle, as well as the line of resistance. These factors play a major role in defining anexercise pattern and the amount of effort requiredand therefore must be evaluated for each prescribedexercise.'"rne of these factors appear to influencethe linear resistance provided by the tubing. Eventhough the resistance increases as joint angle increas-es, the band-to-arm angle and shoulder abductionangle offset the linearity and vary the torque in amanner that represents one of the most commonlyseen strength curves for the majority of musclegroups in the body.'2

In a review of literature, Kulig et all2 showed thatthe strength curve of shoulder abduction was a de-scending pattern, with greatest abduction strengthoccurring early in the range of motion. This is wherethe resistance created by arm length has the least im-pact on resistive torque at the shoulder, and musclemechanics may be more favorable, consequently al-lowing 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 0.5pounds across all tubing colors. This influenced theaccuracy with which we could record some of thesmaller tension values, especially in tests of the yel-

low tubing. Another limitation is the lack of controlfor limb speed. Even though subjects were told toperform slow, controlled movements, it is possiblethat the subjects accelerated the limb, placing an ad-ditional inertial strain on the gauge and inflating therecorded values. However, our finding of statisticallynonsignificant differences between subjects indicatesthat constant tubing tension can be maintained if ex-ercise movements are performed slowly. In addition,the angle measures were approximated from the vid-eotape and digitizing process. Our indirect assess-ment of the range of motion was limited by our abili-ty to coincide the video frame number for joint an-gle measurement with the strain gauge value d i splayed in the frame field. In some analyses this valuewas equal across a number of frames, and when cou-pled with the 0.51b resolution of the gauge, this mayhave skewed our joint angle positions and inevitablyinfluenced the force values. This is why some of ourangle values approximated the intended joint posi-tions under investigation. In addition. we did not usea comprehensive model for calculating the resistivetorque a t the shoulder. To calculate the torquecurves for the isotonic loads, we used the average an-thropometric segment lengths obtained from oursample and did not include individual estimatedlimb weights. Furthermore, our not performing elec-tromyographic analysis limits our discussion to load-ing at the glenohumeral joint and prevents fruitfuldiscussion regarding the role of individual shouldermuscles in performing resistance exercise with elastictubing. However, a recent study by Hintermeister etal" indicated that electromyographic levels in selectshoulder muscles were of adequate intensity whenelastic cords were used as resistance.

Despite these limitations, we feel that the resultsshed light on the effects of elastic exercise on ten-sion development. We recommend further investiga-tions to determine strain values with accelerated ex-ercise movements, especially with eccentric trainingloads and different joint movements, and also investi-gations using electromyographic analysis to deter-mine load sharing among muscles that act as primemovers.CONCLUSION

Our results support the linear response of Thera-Band tubing in providing resistance during shoulderexercise. However, the resistive torque pattern pro-vided by various levels of elastic tubing appears to besimilar to that provided by traditional isotonic exer-cise for shoulder abduction. The minimum and max-imum resistance for each tubing color were identi-fied and can be extrapolated to other exercises thatresult in similar length changes. Additional researchon the biomechanics of elastic band training needsto be performed to more completely delineate the

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advantages and disadvantages o f using elastic bandsas a me th od o f resistance exercise fo r patients in-volved in a rehabilitation program.

ACKNOWLEDGMENTSTh e authors than k the Hygenic Corporation, Ak-

ron, Ohio, fo r supplying the Thera-Band.

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J Orthop Sports Phys Ther Volume 29. Number 7 .July 1999

July1999 RR Hughes

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