WENDELL P. LIEMOHN,' TED A. BAUMGARTNERJ^* AND LAURA H . GAGNON^
'Department of Exercise, Sport, and Leisure Studies, University of Tennessee, Knoxville, Tennessee 37996;-Department of Exercise Science, University of Georgia, Athens, Georgia 30602.
ABSTRACT. Liemohn, W,P,, T.A. Baumgartner, and L.H. Gag-non. Measuring core stability. J. Strength Cond. Res. 19(3):583-586. 2005.—In this study, a 4-item battery of core stability (CS)tests modeled on core stabilization activities used in trainingand rehabilitation researcb was developed, and a measurementschedule was established to maximize internal consistency andstability reliabilities. Specifically, we found that 4 test admin-istrations on each of 4 days produced intraclass correlation co-efficients that in most instances exceeded 0,90 and stability re-liability coefficients on the third and fourth days of testing thatexceeded 0.90 for 2 of tbe tests and 0.80 for the other 2. Thus,it is recommended that in future research, examiners administerthe battery for at least 3 days and consider the data collectedon day 3 as the best estimate of participant CS.
m he term core stability (CS) has attained a highdegree of prominence in the past few years;quite possibly, it may bave emanated from tbeexercises popularized hy the San Francisco
Spine Institute (SFSI) wben the concept of the neutralspine was stressed in their 1989 manual titled DynamicLumbar Stahilization Program (32). During this era, sta-bilization training was used with both athletic and non-athletic populations {27, 29-311. Core stability remains akey component in <a) clinical rehabilitation (12, 23, 28),(b) the training of competitive athletes (15, 16, 21), and(c) the training programs of individuals who are endeav-oring to improve tbeir health and pbysical fitness (1, 5,19).
Panjabi (26) presented a conceptualization of CS (hecalled it spinal stability) that is based on 3 subsystems:the (a) passive spinal column, (b) active spinal muscles,and (c) neural control unit. Drawing from Panjabi, we de-fine CS as the functional integration of the passive spinalcolumn, active spinal muscles, and tbe neural control unitin a manner tbat allows the individual to maintain tbeintervertebral neutral zones within physiologic limitswhile performing activities of daily living.
Following Panjabbi's (26) previously mentioned con-ceptualization scheme, our discussion will emphasize theactive core muscles and the neural control unit, for thepassive spinal column is the least amenable to training.Altbougb the terms core stability and core strengtb aresometimes used intercbangeably, we bave chosen to sub-sume core strengtb within CS. Core stability requires co-ordination in addition to core strength and endurance.
In our discussion of core muscles, we will follow Berg-mark's (4) classification scheme tbat groups core musclesinto either the Global Stabilization System (GSS) or theLocal Stabilization System (LSS). The larger and smallermuscles of the trunk are tbe cbief contributors to the GSS
and the LSS, respectively. The role of the LSS is relatedmore to the coordination and control of motion segmentsthan to the more forceful movements provided by tbemuscles of the GSS that bave larger masses and longermoment arms of force (2). Tbe LSS muscles also are closerto tbe spinal column and thus can provide varying de-gi-ees of segmental control. For example, tbe intertrans-versarii mediales, interspinales, and rotatores are ex-tremely close to the center of rotation of the spinal seg-ments. Their very small pbysiological cross-sectional areaand their higb density of muscle spindles (4.5-7.3 timesricher than the number in the multifidus |24|) suggeststhat they may act primarily as position transducers of tbespinal column (6, 9, 22). This would suggest that tbeseLSS muscles would appear to be particularly importantto the coordination required in CS.
Tbe major purpose of tbis researcb was to develop ameasurement scbedule that would enable us to quantifyCS and maximize internal consistency reliability and sta-bility reliability. In our prior researcb, although internalconsistency reliability was satisfactory, stability reliabil-ity was not (17, 18); this was attributed to the fact thatour CS tests require balance and coordination (that canimprove with repeated testing) in addition to strength.
M E T H O D S
Experimental Approach to the Problem
Wben the SFSI's CS training activities (32) are analyzed,coordination and balance appear to be key elements, foreven in the more difficult tasks, tbe thoracic extensorsare used at but a fraction of tbeir maximum voluntarycontraction (7, 20). Altbough tbere are numerous ways tomeasure strength of tbe core musculature (10, 11, 14, 16),tbese tests emphasize strength and/or endurance, wbere-as performance on the SFSI's stability exercises also re-quires balance and coordination. Cosio-Lima et al. (8)used a standing balance test as an indicator of CS; wechose to try to replicate actual CS training postures inour balance tests.
Because tbe surface area of our force platform is notlarge enough to accommodate postures such as the quad-ruped used in the SFSI's stabilization exercises, we choseto use the Stability Platform (Lafayette Instrument Co,,Lafayette, IN). Tbe Stability Platform is a very sensitiveinstrument tbat was designed for the measurement ofstanding balance with the feet typically placed parallel tothe tilt axis (25, 33); however, the large size of its plat-form (—66 X 106 cm) accommodates postures used in tbeSFSI's CS training program, including Bridging 1.12 andQuadruped Arm Raises 2.9 (32), We used 2 versions ofthe latter test (Figure 1) in our battery, 1 witb the bodyparallel and 1 with the hody perpendicular to the tilt axis.We also added a test in wbicb from a kneeling posture on
583
584 LiE.MOHN, BAUMGARTNEK, AND GAGNON
FIGURE 1. Quadruped arm raise (body parallel to tilt axis).In this test, the suhject alternately raises each arm in concertwith the metronome (i.e., each arm is raised 20 times to shoul-der level in each 3G-second test).
the Stability Platform, subjects alternately raised tbeirarms in time with a metronome; Hodges and Richardson(13) found that there was delay in activation of the trans-versus abdominis as back patients performed this activi-ty. For the latter test, tbe arm raising was done witb themetronome set at 60 bmin '; for tbe 2 quadruped armraise tests, tbe metronome was set at 40 b-min '. All ourhalance tasks were of 30-second duration, and tbe tilt lim-its of tbe balance board were set at 5° to eitber side; withtbis arrangement, the clock counter counts the number ofseconds witbin tbe 30-second test tbat the subject did notmaintain balance within tbe 10" arc. Additional data col-lected hut not reported here included (a) tbe number oftimes tbat tbe subject was outside the 10" arc in eacb 30-second trial and (b) ratings of perceived exertion for eachtest.
SubjectsSixteen university students (9 men, 7 women) free of anyorthopedic disability tbat would have precluded tbeir par-
ticipation volunteered to participate. Men and womenwere combined because our objective was to determinetbe reliability of our test protocol, and our prior researcb(17, 18) did not suggest tbat gender was an importantissue. Tbe procedures were reviewed and approved by ouruniversity's Institutional Review Board; eacb subjectsigned a written informed consent before participating intbis study.
ProceduresBased on our prior investigations (17, 18), we knew tbatcollecting multiple trial scores on eacb day of multipledays was necessary to identify a measurement scbeduletbat would yield reliable test scores because subjectstended to improve performance witb practice. For tbis in-vestigation, we selected 4 tests from our 6-balance-testbattery and administered eacb of tbese tests on 4 dayswith 5 trials administered on eacb day. The 4 days of testadministration were typically spread out over an 8-12-day period. Eacb day a test was administered, tbe testwas explained, and a 20-second trial was given, and tbenthe participants were administered each test once; trials2-5 were similarly administered without the 20-secondpractice period. The score of a participant was the num-her of seconds out of balance, so the smaller a score, thehetter the score. We hypothesized that tbe scores fromtbe first day of testing would he much worse than tbescores from subsequent days of testing, so tbe first-daytrials were considered practice trials for the participantsto learn to perform the test. Also, we hypothesized thattbe first trial for days 2—4 of testing sbould also be con-sidered a practice trial.
Statistical AnalysesIntraclass reliability coefficients for tbe trial scores of aparticipant using a 1-way analysis of variance design (3)were calculated for eacb testing day of each test. Stabilityreliability for the score of a participant on a single dayusing the data from days 2 and 3, days 3 and 4, and days2—4 was estimated using an intraclass reliability coeffi-cient formula from Baumgartner et al. (3).
RESULTSPresented in Table 1 are the trial means for each test andeach day of testing. Tbe trial means for tbe first day of a
TABLE 1. Trial means for each day of testing for each test.
MeanTest lay
1234123412341234
Trial 1
15.410.25.11.6
13.26.24.44.0
10.44.42.92.1
10.46.33.54.3
Trial 2
13.56.63.02.19.74.83.32.87.13.32.82.08.06.64.44.1
Trial 3
10.56.22.92.18.54.73.82.65.82.71.61.85.24.33.53.7
Trial 4
9.46.22.51.87.54.93.12.54.02.12.62.36.94.23.03.0
Trial 5
8.75.62.62.16.94.12.93.14.03.11.62.15.05.63.04.0
Kneeling arm raise
Quad arm raise (parallel)
Quad arm raise (perpendicular)
Bridging
CORE STABILITY 585
TABLE 2. Reliability coeffeients and means for each day oftesting for eacb test.
TABLE 3. Stability reliability of a day sum and means of daysums.
Test Day Reliability Mean
Kneeling arm raise
Quad arm raise (parallel)
Quad arm raise (perpendicular)
Bridging
0.950.940.950.910.910.890.710.780.940.870.900,91
6.12.82.04.63.32.72.82.12.05.23.53.7
test are markedly higher (worse) than the trial means forthe second day of a test as hypothesized. Usually themean for the first trial of a day for any ofthe 4 tests wasthe highest mean for the day. Based on the means re-ported in Table 1, the decision was made to consider day1 of testing as a practice day and the first trial of a testfor days 2-4 as a practice trial. The score of a participantfor a day would then be the mean or sum of the trial 2 -5 scores.
Intraclass reliability coefficients for the sum or meanofthe trial scores of a participant using a 1-way analysisof variance design (3) were calculated for each testing dayof each test. Intraclass reliability coefficients for the sumor mean ofthe trial 2-5 scores within a day and the meanscore for a day are reported in Table 2. The reliabilitycoefficients are high, usually at least 0.90. The 2 reliabil-ity coefficients in the 0.70s for test 3 are low, but reli-ability ofthe test scores for test 3 increased daily. Meansfor testing days decreased considerably from day 2 to day3 but decreased less from day 3 to day 4.
Another decision in establishing a measurementschedule is the number of days to administer the test inorder to obtain a reliable score. Reliability of the scoreswithin a day (internal consistency reliability) must behigh in order to obtain high reliability between days (sta-bility reliability). Stability reliability for the score of aparticipant on a single day using the data from days 2and 3, days 3 and 4, and days 2-4 was estimated usingan intraclass reliability coefficient formula from Baum-gartner et al. (3). Reliability coefficients for the score of aparticipant on a single day using the scores from days 2 -4 were low, ranging from 0.56 to 0.76. Means for daysand stability reliability coefficients using data from 2days are reported in Table 3. Reliability coefficients forthe score of a participant on a single day are low usingthe scores from testing days 2 and 3 but are higher usingthe scores from testing days 3 and 4. Reliability coeffi-cients in the 0.80s are considered good and in the 0.90sare considered high.
DISCUSSION
For each test, 5 trials of the test were administered oneach of 4 days. Participants received an explanation anddemonstration of a test before being tested each day. Wehypothesized that the test scores from the first day oftesting would have to be considered practice to learn toperform the tests. This hypothesis was supported by thedata since for each test the mean trial scores were mark-
TestKneeling arm raise
Quad arm raise (par-allel)
Quad arm raise (per-pendicular)
Bridging
Day
234
234
234234
Mean24.411.2
8.0
18.413.210.8
11.28.48.0
20,814.014.8
Reliability
Days 2and 30.52
0.68
0.51
0.68
Days 3and 4
0.94
0.93
0.84
0,83
edly higher (worse) on the first day than on other days oftesting. Also, we hypothesized that the test scores fromthe first trial of a day would have to be considered prac-tice/warm-up to perform the test. This hypothesis wassupported by the data since typically the mean for trial 1was the highest (worst) mean. In fact, for the first 3 daysof testing, the mean for trial 1 was always the highestmean. Thus, internal consistency reliability was calculat-ed for days 2-4 of testing using the scores for trials 2-5.Internal consistency reliability was acceptable on testingdays 2-4 for all 4 tests. Internal consistency reliabilitytended to be best on the fourth day of testing. Trial meansfor a day were fairly consistent for trials 2-5,
Stability reliability coefficients for the score of a par-ticipant collected on a single day were calculated usingthe scores for testing days 2 and 3 and for testing days 3and 4. We had hoped to find sufficiently high stabilityreliability coefficients to be able to suggest that in thefuture only testing on days 1 and 2 would be necessary.However, stability reliability was low using the testscores for days 2 and 3 and sufficiently high using thetest scores for days 3 and 4. Means for the days decreasedmore from day 2 to day 3 than from day 3 to day 4. Thus,test scores are fairly stable from day 3 to day 4 of testing.The intraclass correlation coefficient used to estimate sta-bility reliability is affected by changes in the mean scorefrom day to day. The high stability reliability coefficientsobtained suggest that the score and rank of a participantin a group is fairly stable from day 3 of testing to day 4of testing.
Based on the findings in this study, administering 5trials on each of 3 days of the Stability Platform testsused in this study is sufficient to obtain a test score withgood internal and stability reliability. The test score of aparticipant would be the sum or mean of trials 2-5 onday 3 of testing.
PRACTICAL APPLICATIONS
Now that we are comfortable with both the internal andthe stability reliability of our measurement schedule forour 4 CS tests on the Stahility Platform, we are testingsubjects on the previously mentioned tests as well as ontheir performance on a series of core strength activitiesthat require varying degrees of coordination (e.g., floor vs.
586 LIEMOHN, BAUMGARTNER, AND GAGNON
Swiss-ball strength training activities/tests). We also planto use one of our CS tests as tbe primary dependent var-iable when we examine tbe effectiveness of a Pilatestraining program against a more conventional one in therehabilitation of patients witb low baek pain.
REFERENCES
1. ALLEN, S,, G,A. DUDLEY, M, IOSIA, D. STANFORTH, AND B.STEHERWALD. Core strength training, Gatoraide Sports ScienceInstitute, 2002, 13(1); 14.
2. AROKOSKt, J.P., M. KAAIIKAANPAA, T. VALTA, L JUVONEN, J .PARTANEN, AND S, TAIMELA. Back and hip extensor musclefunction during therapeutic exercise. Arch. Phys. Med. Rehabil.80:842-850, 1999.
3. BAtJMGARTNER, T.A., A.S. JACKSON, M.T. MAHAR, AND D.A.RowE. Measurement for Evaluation in Physical Education andExercise Science (7th ed.). Madison, WI: McGraw-Hill, 2003.
4. BERGMARK, A. Stability of the lumbar spine: A study in me-chanical engineering, Acla Orthop. Scand. 230(Suppl,);20-24,1989,
5. BLACK. S.A. Training the core. Fitness Manage. (October):60-63, 2001.
6. BOGDUK, N. Clinical Anatomy of the Lumbar Spine and Sa-crum (3rd ed.), London: Churchill Livingstone, 1998,
7. CHOLEWICKI.J., M. PANJABI, AND A, KHACHATRYAN, Stabilizingfunction of trunk flexor-extensor muscles around a neutralspine posture. Spine 22:2207-2212. 1997.
8. Cosio-LiMA, L,M,, K,L, REYNOLDS, C. WINTER, V. PAOLONE,AND M.T. JONES. Effects of physioball and conventional floorexercises on early phase adaptations in back and abdominalcore stability and balance in women, J. Strength Cond. Res. 17:721-725, 2003.
9. CRISCO, J.J,, AND M.M. PANJABI, The intersegmental and mul-tisegmental muscles of tbe spine: A biomecbanical model com-paring lateral stabilising potential. Spine 16:793-799, 1991,
10. FRITZ, J ,M,, AND G.E. HICKS, Exercise protocols for low backpain. In: Exercise Prescription and the Back. W, Liemobn, ed.New York: McGraw-Hill Medical Publishing Division, 2001. pp.167-181.
11. GRAVES, J.E., M.L. POLLOCK, AND C.X. BRYANT. Assessment ofmuscular strength and endurance. In: ACSM's Resource Man-ual for Guideline.'^ for Exercise Testing and Prescription. J.L,Roitman, ed. Baltimore: Lippincott Williams & Wiikins, 2001.pp. 448-155.
12. HIDES, J.A., G.A, JULL, AND C,A. RICHARDSON. Long-term ef-fects of specific stabilizing exercises for flrst-episode low backpain. Spine 26:E243-E248. 2001.
13. HODGES, P.W., AND C.A. RICHARDSON Inefficient muscular sta-bilisation of tbe lumbar spine associated with low back pain:A motor control evaluation of transversus abdominis. Spine 21:2640-2650. 1996.
14. ITO, T., O. SHIRADO, H . SUZUKI, M. TAKAHASHI, K. KANEDA,AND T.E. STRAX. Lumbar trunk muscle endurance testing: Aninexpensive alternative to a macbine for evaluation. Arch.Phys. Med. Rehabil. ll:lb'13. 1996.
15. JEFTREYS, L Developing a progressive core stability program.Strength Cond. J. 24(5):65-66. 2002.
16. LEETUN, D.T., M.L. IRELAND, J.D. WILLSON, B.T, BALIJ\NTYNE,AND I.M. DAVIS. Core stability measures as risk factors for low-er extremity injury in athletes. Med. Sci. Sports Exerc. 36:926—934. 2004.
17. LIEMOHN, W,, T,A, BAUMGARTNER, AND K.A, KELLY, Core sta-bility: The genesis of a test battery. Med. Sci. Sports Exerc.35(Suppl, 5):S275,- 2003.
18. LIEMOHN, W., R.C, JOHNSON, J.C. SANDERS, AND J. WOODS.Measuring cores strength and core stability: A pilot study. Med.Sci. Sports Exerc. 34(Suppl, 5):S153. 2002.
19. LIEMOHN, W., AND G. PARISER, Core strengtb: Implications forfitness and low back pain, ACSM's Health & Fitness J. 6(5):10-16, 2002,
20. McGlLL, S.M, Low Back Disorders: Evidence-Based Preventionand Rehabilitation. Champaign, IL: Human Kinetics, 2002.
21. McGiLL, S.M, Low back stability: From formal description toissues for performance and rehabibtation. Exerc. Sport Sci. Rev.29:26-31. 2001.
22. McGiLL, S.M. Mechanics and pathomechanics of muscles act-ing on the lumbar spine. In: Kinesiology: The Mechanics andPathomechanics of Human Movement. C.A. Oatis, ed, Philadel-phia: Lippincott Williams & Wilkins, 2004, pp. 563-575.
23. McGiLL, S.M,, AND J. CHOLEWICKI. Biomechanical basis forstability: An explanation to enbance clinical utility. J. Orthop.Sports Phys. Ther. 31:96-100, 2001,
24. NiTZ. A.J., AND D. PECK. Comparison of muscle spindle con-centrations in large and small buman epaxial muscles actingin parallel combinations. Am. Surg. 52:273-277. 1986.
25. NORDAHL, S.H., T, AASEN, B.M. DYRKORN, S. EIDSVIK, AND O.MoLVAER. Static stabilometry and repeated testing in a normalpopulation, Mnat. Space Environ. Med. 71:889-893. 2000.
26. PANJABI, M.M, The stabilizing system of the spine, part I.Function, dysfunction, adaptation, and enhancement, J. SpinalDisord. 5:383-389. 1992.
27. SAAL, J.A. Dynamic muscular stabilization in the nonoperativetreatment of lumhar pain syndromes. Orthop. Rev. 19:691-700.1990.
28. SAAL, J.A, Natural history and nonoperative treatment of lum-bar disc herniation. Spine 21(Suppl. 24):S2-S9. 1996.
29. SAAL, J.A. Rebabilitation of football players with lumbar spineinjury (part 1 of 2), Physician Sports Med. 16(9):61-68. 1988.
30. SAAL, J.A, Rebabilitation of football players with lumbar spineinjury (part 2 of 2). Physician Sports Med. 16(10): 117-125.1988,
31. SAAL, J.A., AND J.S. SAAL. Nonoperative treatment of herniatedlumbar intervertebral disc witb radiculopathy—An outcomestudy. Spine 14:431-437. 1989.
32. SAN FRANCISCO SPINE INSTITLTTE. Dynamic Lumbar Stabiliza-tion Program. San Francisco: San Francisco Spine Institute,1989.
33. SHEA, C.H., AND G. WLILE. Enhancing motor learning tbrougbexternal-focus instructions and feedback. Hum. Mov. Sci. 18:553-571. 1999.
![Ch 5: Measurement Concepts. Reliability Reliability refers to the consistency or stability of a measure of behavior [p92] If you weighed yourself.](https://static.documents.pub/doc/80x56/551bd5c6550346af588b57e6/ch-5-measurement-concepts-reliability-reliability-refers-to-the-consistency-or-stability-of-a-measure-of-behavior-p92-if-you-weighed-yourself.jpg)
