J

O

Ta

K

a

b

R

I

Ti

cGT

1d

ournal of Science and Medicine in Sport (2007) 10, 447—455

RIGINAL PAPER

runk muscle endurance tests: Reliability,nd gender differences in athletes

errie Evansa,b,∗, Kathryn M. Refshaugea, Roger Adamsa

School of Physiotherapy, The University of Sydney, AustraliaSchool of Physiotherapy and Exercise Science, Griffith University, Australia

eceived 21 August 2006; accepted 7 September 2006

KEYWORDSTrunk muscle endurance;Reliability;Athletes;Gender

Summary Adequate trunk muscle endurance may play an important role in injury-free performance among athletes. However, reliability of tests of isometric trunkmuscle endurance in common use has not been clearly established and few stud-ies have reported normative data for athletes. This study first examined intra-raterand inter-rater reliability of the side bridge endurance test and a test of trunkflexor endurance in a group of non-athletes, then measured performance of a groupof elite athletes on tests of trunk muscle endurance commonly used in the clinic.The side bridge endurance test and the trunk flexor endurance test were found tohave high intra-rater and inter-rater reliability, albeit with relatively large stan-dard error of measurement (S.E.M.) values. In contrast with previous studies ofnon-athletes, male athletes had equivalent holding times on the Biering—Sørensentrunk extensor endurance test to those of female athletes. However, female ath-letes had significantly lower holding times on the side bridge endurance tests than

their male counterparts. The implication of the significant difference in enduranceperformance between male and female athletes in some muscle groups but notothers is that testing and training of trunk muscle endurance should be ‘mul-tidirectional’ for all athletes who aim to optimise performance and minimiseinjury risk.

Aus

m

© 2006 Sports Medicine

ntroduction

raining programs undertaken by athletes oftenncorporate exercises designed to optimise trunk

∗ Corresponding author at: School of Physiotherapy and Exer-ise Science, Griffith University, Gold Coast Campus, PMB 50,old Coast Mail Centre, Qld 9726, Australia.el.: +61 7 5552 8821; fax: +61 7 5552 8674.

E-mail address: Kerrie.Evans@griffith.edu.au (K. Evans).

trtfifailb

440-2440/$ — see front matter © 2006 Sports Medicine Australia. Publisheoi:10.1016/j.jsams.2006.09.003

tralia. Published by Elsevier Ltd. All rights reserved.

uscle strength and endurance, and it is suggestedhat these exercises should reflect the multidi-ectional nature of the stability demands on therunk during athletic performance.1,2 While suf-cient trunk muscle strength may be necessaryor some sport-specific tasks,3 evidence, at least

mong non-athlete groups, suggests that the abil-ty of the trunk muscles to maintain appropriateevels of activation over long periods of time maye more important than maximum strength in terms

d by Elsevier Ltd. All rights reserved.

K. Evans et al.

celwrlmtt

sdttttoaertwHdio

tt

448

of protecting the passive structures of the lumbarspine from injury.4—6 It has also been suggested thatsufficient trunk muscle endurance contributes tospinal stability over strenuous and prolonged physi-cal tasks7 and therefore may be important for manyof the complex and demanding tasks performedby athletes. However, from either a performanceperspective or an injury prevention perspective,the role of isometric muscle endurance testing andtraining for athletes is unclear.

A number of isometric tests of trunk mus-cle endurance have been described for the trunkextensors, flexors and lateral musculature of thetrunk.6,8—10 Typically these tests require minimal,inexpensive equipment, and are safe and simpleto employ in clinical environments where perfor-mance is evaluated by recording the maximumtime a person can maintain the test position. Itis important that tests chosen to evaluate isomet-ric trunk muscle endurance have good reliabilityto allow their use in studies comparing trainingprotocols, predicting injury, or for calculation ofthe training change necessary to infer improve-ment. Except for the Biering—Sørensen test oftrunk extensor endurance (Fig. 1), reliability ofother common isometric trunk muscle tests isnot well established,11,12 with conflicting findingsreported, as well as difficulties in implementingtest protocols.11,13

Of the isometric trunk endurance tests describedin the literature, the Biering—Sørensen test oftrunk extensor endurance has received the mostattention. This test has been shown to have goodreliability whether or not there is a history oflow back pain (LBP), with ICC(1,1) ≥0.77.14 Innon-athlete populations, poor performance on theBiering—Sørensen test has been shown to predictfuture episodes of LBP,5,6 although this has not beendemonstrated in the athlete populations investi-gated to date.15,16 The results however may be

specific to the types of sports investigated in thesestudies (i.e., golfers, basketballers, track and fieldathletes) and cannot necessarily be generalised toathletes from other sports.

Figure 1 The Biering—Sørensen test of trunk extensorendurance6.

thprntecbw

afplA

Figure 2 Side bridge endurance test18.

Rather than a fixed, absolute level of enduranceapacity of the trunk muscle groups, it is reducedxtensor endurance relative to the trunk flexors andateral musculature that has been found in peopleith a history of low back trouble.17 Although this

esult has not yet been clearly demonstrated in ath-ete populations, reliable tests of the lateral trunkusculature and trunk flexors are required in order

o examine whether or not this relationship holdsrue.

For testing the lateral trunk musculature, theide support or side bridge exercise (Fig. 2)escribed by McGill et al.18 has been suggestedo optimally challenge quadratus lumborum andhe muscles of the anterolateral trunk wall.2,8 Inheir study, McGill et al.18 recorded the holdingimes of 75 healthy subjects (mean age 21 years)n endurance tests for the trunk extensors, flexorsnd lateral flexors. Reliability of these tests wasxamined on a small subset of five subjects. Intra-ater reliability was excellent (ICC ≥ 0.97) for allests over 5 consecutive days, and remained highhen follow-up data at 8 weeks were included.owever, the reliability component of this studyid not include inter-rater reliability or confidencentervals and standard deviations so the precisionf the tests could not be calculated.

A number of isometric endurance tests for therunk flexors have been described8—10 and, whilehe method evaluated by McGill et al.18 challengeshe abdominal musculature,8 significantly longerolding times than those reported in the originalaper have been observed by Chen et al.19 For thiseason, and because these latter researchers didot report reliability data, this test was examined inhe present study. An alternate test of trunk flexorndurance described by Ito et al.9 was included foromparison, since the test—retest ICCs reported foroth healthy subjects and those with chronic LBPere 0.95 and 0.90, respectively.To determine if trunk muscle endurance testing

nd training is useful for athletes from a per-

ormance perspective and/or an injury preventionerspective, the tests chosen to evaluate an ath-ete’s trunk muscle endurance need good reliability.dditionally, in order to help interpret the results of

Trunk muscle endurance tests: Reliability, and gender differences in athletes 449

Table 1 Physical characteristics, and holding times of participants from occasion 1 (Part 1)

Mean (S.D.) Range

Age (years) 35.3 (14.4) 16—57Weight (kg) 74.7 (14.2) 49—105Height (cm) 173.3 (9.9) 152—188BMI (kg/m2) 24.7 (2.8) 19.2—30.7Right side bridge endurance test (s) 87.5 (36.4) 20—203

92.0 (45.8) 19—251353.3 (271.9) 53—900

ttbfitwce(te

M

Pe

TiseattlcttswRf

ST3iuSRab

medical conditions that contraindicated vigorousexercise. No subject had to be excluded becauseof these criteria.

RatersTwo raters, one an exercise science graduate andthe other a manipulative physiotherapist, per-formed all measurements. Prior to data collection,the raters practised using the test protocols toensure standardised procedures were employed.

ProtocolBoth raters applied each test, in random order, ontwo occasions separated by 2 weeks. Prior to per-formance of each test, the raters explained anddemonstrated the test procedure. Measurementsfrom the two raters were recorded on separate datacollection forms to ensure that they were blinded toeach other’s results and their own previous results.

VariablesThe side bridge endurance (Fig. 2) and trunk flexorendurance tests (Fig. 3) were measured using themethod described by McGill et al.18 For the sidebridge test, subjects lay on their side with theirlegs extended, resting on their forearm with theelbow flexed to 90◦. Subjects were instructed tolift the hip off the bed and maintain a straight linewith the whole body throughout the test.18 Thestarting position for the trunk flexor endurance testinvolved positioning subjects on a plinth with their

Left side bridge endurance test (s)60◦ trunk flexor endurance test (s)

runk muscle endurance testing and assist in settingraining targets, normative data are required foroth male and female athletes participating in dif-erent sports. In the present study, intra-rater andnter-rater reliability of the side bridge enduranceest and the trunk flexor endurance test at 60◦ere first examined using a non-athlete sample ofonvenience. The second part of the study thenxamined the performance of male and female elitei.e., state level) athletes from different sports onests commonly employed to measure trunk musclendurance.

ethods

art 1: reliability of trunk musclendurance tests

he aim of the first part of the study was to examinentra-rater and inter-rater reliability of the rightide bridge endurance test, the left side bridgendurance test and the trunk flexor endurance testt 60◦ in a group of healthy subjects. Examininghe reliability of a test for subjects who are likelyo have a restricted range of scores may lead toow reliability coefficients.20 So, the subjects hereovered the spectrum from no sport participationhrough to consistent recreational sport and it washerefore expected that this group would repre-ent a range of endurance capabilities. This studyas approved by The University of Sydney Humanesearch Ethics Committee and consent was gainedrom all subjects prior to data collection.

ubjectswenty-four subjects (16 males, 8 females), aged5.3 ± 14.4 years (mean ± S.D.) and with body massndex (BMI) between 19.2 and 30.7 kg/m2, vol-nteered to participate in the study (Table 1).

ubjects completed a modified Physical Activityeadiness Questionnaire (PAR-Q)21 and were askedbout any history of cardiovascular disease, dia-etes, previous back surgery, orthopaedic and other Figure 3 Trunk flexor endurance test at 60◦ 18.

450

RSapepe

PT1et

VFpljlt(mTsabp

suatwiiab

Figure 4 Ito et al.9 trunk flexor endurance test.

back resting against a wedge that maintained 60◦flexion from the horizontal. Knees were flexed to90◦ and the feet secured with a seat belt (Fig. 3).

Part 2: application of trunk muscleendurance tests to athlete group

The purpose of the second part of this study wasto examine the performance of a group of maleand female elite athletes on a set of trunk mus-cle endurance tests. Trunk extensor endurance wasmeasured using the Biering—Sørensen endurancetest14 (Fig. 1). Side bridge endurance was mea-sured using the protocol described in Part 1 of thisstudy18 and trunk flexor endurance using two dif-ferent methods: the trunk flexor endurance test at60◦18 and the Ito et al.9 trunk flexor endurance test(Fig. 4). In addition to approval from The Univer-sity of Sydney Human Research Ethics Committee,this part of the study also gained approval from theinstitution with which the athletes were affiliatedand consent was gained from all subjects prior todata collection.

SubjectsA total of 79 elite (state level) athletes, aged21.2 ± 2.3 years (mean ± S.D.), from six differentsports volunteered to participate (Table 2).

DIu

Table 2 Characteristics of athlete groups

Sport Gender N

Netball Female 1Water polo Male 1Hockey Female 1Soccer Male 1Soccer FemaleRowing MaleRowing FemaleGolf MaleGolf Female

Total 7

K. Evans et al.

aterso that athletes could be tested within their squadnd their usual training time, a total of 18 raterserformed the measurements. Ten raters werexercise science graduates and eight raters werehysiotherapists with a mean of 5.8 years experi-nce.

rotocolests were conducted in random order with at least0 min rest between tests. Prior to performance ofach test, the rater explained and demonstratedhe test to subjects using standardised instructions.

ariablesor trunk extensor endurance (Fig. 1), subjects layrone with the upper body resting on a chair and theower body fixed to a plinth by three seat belts. Sub-ects were asked to cross their arms over the chest,ift the upper body and maintain a horizontal posi-ion for as long as possible.6 Side bridge enduranceFig. 2) and the trunk flexor test at 60◦ (Fig. 3) wereeasured using the protocols described in Part 1.he Ito et al.9 trunk flexor endurance test involvedubjects lying supine, arms crossed over their chestnd hips and knees flexed to 90◦ (Fig. 4). The testegins when subjects lift their upper body off thelinth.

For all endurance tests, in both Parts 1 and 2,ubjects were encouraged to hold the test positionntil fatigue, and were given feedback if they devi-ted from this position. Tests were terminated ifhey could not maintain the position or if thereere any obvious signs of fatigue or a significant

ncrease in their pain or other symptoms. The max-mum holding time was recorded in seconds using

stopwatch. Subjects had at least 10 min restetween consecutive tests.

ata analysisntra-rater and inter-rater reliability was estimatedsing intraclass correlation coefficients, ICC(3,1)

umber of subjects Mean age (S.D.)

4 22.8 (2.1)2 20.8 (3.9)4 22.5 (3.3)2 17.3 (1.3)8 20.4 (3.8)3 21.3 (0.6)5 21.0 (0.7)5 21.8 (2.0)6 22.8 (3.3)

9 21.2 (2.3)

Trunk muscle endurance tests: Reliability, and gender differences in athletes 451

Table 3 Mean holding times and intra-rater reliability for the right and left side bridge endurance tests and thetrunk flexor endurance test at 60◦

Test Rater Occasion 1,mean (S.D.) (s)

Occasion 2,mean (S.D.) (s)

p-Value(t-test)

ICC(3,1) (95% CI) S.E.M.

Right side bridge A 87.5 (36.4) 81.5 (34.2) 0.18 0.82 (0.63—0.92) 14.9endurance test B 80.8 (37.5) 79.6 (32.5) 0.79 0.81 (0.61—0.91) 15.2Left side bridge A 92.0 (45.8) 83.4 (45.0) 0.10 0.85 (0.69—0.93) 17.4endurance test B 82.8 (46.3) 83.6 (37.8) 0.88 0.82 (0.63—0.92) 17.8

◦ .1 (2.09

afiecetsFcieafws

R

Pe

IIwS

fe

IIa(tflTmwst

Pe

Buae

60 trunk flexor A 353.3 (271.9) 373endurance test B 351.8 (274.5) 365

nd ICC(2,1), respectively.22 For each ICC, 95% con-dence intervals (CI) were generated. The standardrror of measurement (S.E.M.) for each test wasalculated as the square root of the mean squarerror from the appropriate analysis of variance23

o provide an estimate of the precision of the mea-urement, expressed in the units of the measure.or the athlete group, Pearson’s product momentorrelation coefficient (r) was calculated to exam-ne the relationship between performance on eachndurance test. Independent-samples t-tests werelso conducted to compare results for male andemale subjects on the endurance tests. Analysisas performed using SPSS-Windows software (Ver-

ion 11.5.0).

esults

art 1: reliability of trunk musclendurance tests

ntra-rater reliabilityntra-rater reliability values were high for all tests,ith the lowest ICC(3,1) being 0.81 (Table 3)..E.M.s for the side bridge endurance tests ranged

lapa

Table 4 Mean holding times and inter-rater reliability for60◦ trunk flexor endurance test for occasions 1 and 2

Test Rater A, mean(S.D.) (s)

Rat(S.D

Occasion 1Right side bridge endurance test 87.5 (36.4) 80Left side bridge endurance test 92.0 (45.8) 8260◦ trunk flexor endurance test† 362.5 (274.1) 351

Occasion 2Right side bridge endurance test 81.5 (34.2) 79Left side bridge endurance test 83.4 (45.0) 8360◦ trunk flexor endurance test† 373.1 (253.7) 361† One female subject, due to cyclic pain, could not complete a

between mean values reported here and those reported in Table 3.

53.7) 0.26 0.95 (0.89—0.98) 59.1(255.9) 0.47 0.95 (0.88—0.98) 77.6

rom 14.9 to 17.8 s and, for the trunk flexorndurance test, from 59.1 to 77.6 s (Table 3).

nter-rater reliabilitynter-rater reliability values were also high forll tests, with the lowest ICC(2,1) being 0.82Table 4). S.E.M.s for the side bridge enduranceests ranged from 10.5 to 18.9 s and, for the trunkexor endurance test, from 50.2 to 60.2 s (Table 4).here were no significant inter-rater differences inean values obtained except on the first occasion,here Rater A recorded significantly longer right

ide bridge endurance times (p = 0.04). This was nothe case on the second occasion.

art 2: application of trunk musclendurance tests to athlete group

ecause of time constraints from training sched-les, not all tests were completed by all 79thletes. The Biering—Sørensen and side bridgendurance tests were completed by >95% of ath-

etes. The trunk flexor endurance test at 60◦nd Ito trunk flexor endurance tests were com-leted by 24% of subjects. Mean holding timesnd standard deviations are shown in Table 5. The

the right and left side bridge endurance tests and the

er B, mean.) (s)

p-Value(t-test)

ICC(2,1) (95% CI) S.E.M.

.8 (37.5) 0.04 0.91 (0.78—0.96) 10.5

.8 (46.3) 0.11 0.82 (0.63—0.92) 18.9

.8 (274.5) 0.49 0.97 (0.92—0.99) 60.2

.6 (32.5) 0.57 0.89 (0.77—0.95) 11.1

.6 (37.8) 0.95 0.91 (0.81—0.96) 12.4

.4 (251.0) 0.32 0.98 (0.94—0.99) 50.2

trunk flexor endurance test, thereby causing the differences

452 K. Evans et al.

Table 5 Mean holding times for the five isometric trunk endurance tests performed by the athletes

All athletes Male athletes Female athletes

n Mean (S.D.) (s) n Mean (S.D.) (s) n Mean (S.D.) (s)

Biering—Sørensen 76 163.6 (50.7) 29 157.4 (42.9) 47 167.4 (55.0)Right side bridge 75 104.8 (44.1) 29 126.6 (44.9) 46 91.1 (38.0)*

Left side bridge 77 103.0 (41.3) 30 121.2 (44.4) 47 91.4 (35.0)**

Trunk flexor 19 223.0 (134.4) 8 224.4 (128.0) 11 222.0 (145.1)Ito trunk flexor 19 148.8 (97.7) 8 162.6 (116.5) 11 138.7 (86.1)

Tests where holding times were significantly lower for female athletes than male athletes are indicated by asterisks.

sardtttsbs

D

Imrsetwgh

* p = 0.000.** p = 0.002.

holding time for the Biering—Sørensen trunk exten-sor endurance test was (mean ± S.D.) 164 ± 51 s,range 59—320 s. For the right and left side bridgeendurance tests, holding times were, respectively,105 ± 44 s, range 35—259 s, and 103 ± 41 s, range34—238 s (Table 5). The holding time for the trunkflexor endurance test18 was 223 ± 134 s, range70—480 s, and for the Ito trunk flexor endurancetest, the mean holding time was 149 ± 98 s, range23—381 s.

Relationship between performance on theendurance testsPerformance on the right and left side bridgeendurance tests was strongly correlated (r = 0.86and p = 0.01). Performance on the Biering—Sørensentest was significantly related to the left sidebridge endurance test time but with low correla-tion (r = 0.26 and p = 0.01).24 The relationship withright side bridge time was similarly low (r = 0.20and p = 0.05). There were no other significant rela-tionships among performances on the endurancetests.

Gender differencesMale athletes achieved significantly longerendurance times on both the right and left

ht

d

Table 6 Mean side bridge holding times for male and fema

Sport Gender Right side bridgeholding time (s)

Netball Female 75.9Water polo Male 132.0Hockey Female 113.8Soccer Male 133.8Soccer Female 85.1Rowing Male 112.0Rowing Female 91.0Golf Male 108.4Golf Female 79.8

ide bridge endurance tests than their femalethlete counterparts (p = 0.001 and p = 0.002,espectively). However, male and female athletesid not differ in terms of their performance onhe Biering—Sørensen trunk extensor test, nor didhe smaller subgroup of athletes who performedhe trunk flexor endurance tests demonstrate anyignificant gender difference. Results for the sideridge endurance tests for athletes from individualports are presented in Table 6.

iscussion

n the group of non-athletes whose level of involve-ent in sport ranged from none to consistent

ecreational, reliability values associated with theide bridge endurance tests and the trunk flexorndurance test at 60◦ were all >0.80. As expected,he lowest holding times on the endurance testsere recorded by participants in the non-athleteroup, yet this group also produced two of the threeighest scores, suggesting that this group had the

eterogeneity needed to examine reliability of therunk muscle endurance tests.

ICCs for the side bridge endurance tests con-ucted here with 24 subjects were all ≥0.81. While

le athletes in different sports

Left side bridgeholding time (s)

Mean sidebridge time (s)

74.4 75.2 (6.6)119.9 125.4 (18.5)111.9 112.9 (10.9)128.7 131.3 (10.8)93.4 89.3 (8.5)

115.7 113.8 (13.2)101.2 96.1 (11.8)109.0 108.7 (21.0)72.5 77.4 (19.2)

T er d

trvmaicrimmctrTartadoea3wstffutrtMtmhgtwWtt

patiipwfhcsl

settdis(imiatpfcaaacttlt

fBttwbfatsttcvbtttl

tw(wed

runk muscle endurance tests: Reliability, and gend

hese results indicate that these tests have higheliability,24 the ICCs were lower than those pre-iously reported (ICC ≥ 0.96) when McGill et al.18

easured five subjects. If the side bridge testsre to be used in making program decisions forndividual athletes, information relating to the pre-ision or the consistency of the measurement isequired. The measure of statistical consistencys the S.E.M., and it has the same units as theeasurement of interest and influences the mini-um detectable change (MDC); i.e., the minimum

hange required in a person’s score to be confidento a given degree that true change has occurred,ather than change due to measurement error.24

he MDC, at the 90% confidence level, is calculateds

√2 × 1.64 × S.E.M.24 For both raters on both the

ight and left side bridge endurance tests, rela-ively large changes in an individual’s holding timesre required before a clinician could be 90% confi-ent that change beyond measurement error hasccurred. For example, for the right side bridgendurance test, Rater A showed a S.E.M. of 14.9 s,nd thus a MDC, at the 90% confidence level, of4.6 s. Given that the mean for Rater A for this testas 87.5 s, a person would have to score 122 s on the

econd occasion before there could be confidencehat a true change had occurred. Unfortunately,or many tests in sports science the MDCs requiredor this level of certainty about improvement arenattainably large,25 and it is therefore necessaryo consider the consequences of making decisionsegarding individuals at a level of certainty lesshan that typically employed for statistical tests.26

easurement error may be associated with the ini-ial or subsequent testing occasions. It would seemore likely that a person would score lower than

is/her true endurance capacity; thus training tar-ets may be set too low or, in subsequent testing,he clinician assumes that a person has not changedhen in fact his/her endurance capability has.hether a test’s level of precision is acceptable,

herefore, may depend on the intended use of theest.

Adding another element to an athlete’s physicalreparation program, even if it was included afterfalse positive endurance test score, would seem

o be relatively benign. With reference to chang-ng an endurance time by training, other sources ofnformation not evaluated in the present study mayrovide evidence relevant to decision-making abouthat constitute clinically important/significant dif-

erences. For example, if patients improved their

olding time by only a small amount but their per-eived level of effort in doing so was lower, this mayupport inferring improvement from change valuesess than the MDC.

dtay

ifferences in athletes 453

Although the male and female athletes in thistudy achieved similar times on the trunk extensorndurance test, the side bridge endurance times ofhe male athletes were significantly greater thanhose of the female athletes. Notably, when theifferent sports included in the study were exam-ned separately, this effect was observed in allports where both males and females participatede.g., soccer, rowing and golf). Thus the differencen lateral trunk muscle endurance observed hereay possibly be attributed to gender differences

n anatomic structure or muscle mass distribution,s it does not appear to be sport-specific. Alterna-ively, this gender-based result may due to trainingreferences; i.e., the training programs designedor female athletes may not include sufficient spe-ific endurance exercises for the muscles of thenterolateral trunk. Notably, other studies havelso found significant differences between malesnd females in the performance on trunk mus-le endurance tests. For example, consistent withhe present findings, male basketballers and malerack athletes16 and healthy male subjects18 all hadonger holding times on the side bridge enduranceest than their female counterparts.

Several studies of non-athletic populations haveound females to have longer holding times on theiering—Sørensen test of trunk extensor endurancehan males,27,28 although this was not the case withhe group of athletes examined in this study norith the group of athletes in the study conductedy Leetun et al.16 where holding times were similaror both sexes. By virtue of participating in sport atn elite level, male athletes may develop greaterrunk extensor muscle endurance and thereforecore equivalent trunk extensor endurance timeso female athletes. Studies examining the contribu-ions from other factors are needed before such aonclusion can be reached. However, levels of moti-ation, self-efficacy and body mass index27 have alleen shown to influence a person’s holding time onhe Biering—Sørensen test, so further studies inves-igating these factors, as well as the influence ofraining preferences among male and female ath-etes, are warranted.

Although high ICC values were obtained for therunk flexor endurance test at 60◦, the S.E.M.sere large and the mean values (>350 s) and S.D.s

>±253.7) observed in Part 1 of the present studyere much larger than those reported by McGillt al.18 where the mean ± S.D. was 147 ± 90 s,espite our adherence to the protocol as originally

escribed. The findings here are, however, consis-ent with the results of Chen et al.19 who reportedn average holding time of 375.4 s (±252.5 s) foroung, healthy female subjects.

R

454

Accordingly, the Ito et al.9 test was includedin the present study as an alternate test of trunkflexor endurance. This test has been suggested tohave good reliability and may reduce the likelihoodof exacerbating low back symptoms by minimis-ing lumbar lordosis during the test procedure.9

Although male athletes recorded longer holdingtimes than the female athletes on this test, thedifference was not significant. However, becauseboth the trunk flexor endurance tests were admin-istered to only 24% of the athlete group, there wascorrespondingly lower power for detecting genderdifferences on these tests.

From a performance perspective, the signifi-cance of the difference between male and femaleathletes in performance of some endurance testsbut not others is unknown. From an injury perspec-tive, while Leetun et al.16 found that performanceon the side bridge endurance test did not predictfuture lower limb or low back injury for basket-ballers or track athletes, Evans et al.15 reportedthat it was those young male elite golfers whohad a right side deficit relative to their left sidein holding time on the side bridge endurance testwho were more likely to report future episodesof moderate—severe LBP. Since the relationshipbetween anterolateral trunk muscle endurance andLBP may be sport- and/or gender-specific, fur-ther studies of athletes from different sports arewarranted. As well, assessment of specific train-ing protocols aimed at improving trunk lateralflexor endurance could be examined in a test ongroups of subjects in a randomised controlled trialdesign.

Conclusion

The side bridge endurance test has high intra-raterand inter-rater reliability and may be appropriatefor use in clinical environments for testing lateraltrunk muscle endurance, establishing treatmentgoals and monitoring progress, although relativelylarge changes in holding times are required tobe confident true change has occurred. Consis-tent with other findings and recommendations, datahere suggest that no single endurance test pro-vides information about trunk muscle endurance inall four directions. The implication of the signifi-cant difference in endurance performance betweenmale and female athletes on some trunk muscle

tests but not others is that both trunk muscleendurance testing and training should be ‘multi-directional’ for all athletes who aim to optimiseperformance and minimise injury risk.

K. Evans et al.

Practical implications

1. Isometric tests of trunk muscle endurancerequire minimal, inexpensive equipment andare safe and simple to employ in clinical set-tings.

2. While the side bridge endurance test hashigh reliability, a relatively large change ina person’s holding time following training isrequired, to be confident a true change hasoccurred.

3. Male and female state-level athletes inhockey, golf and rowing have similar holdingtimes on the Biering-Sørensen test of trunkextensor endurance and on two tests of trunkflexor endurance.

4. Male athletes in these sports have signifi-cantly longer side-bridge holding times thantheir female counterparts.

5. Trunk muscle endurance should be testedand trained for multi-directional competenceirrespective of gender.

eferences

1. Barr KP, Griggs M, Cadby T. Lumbar stabilization: core con-cepts and current literature, Part 1. Am J Phys Med Rehabil2005;84(6):473—80.

2. Kavcic N, Grenier S, McGill SM. Determining the stabiliz-ing role of individual torso muscles during rehabilitationexercises. Spine 2004;29(11):1254—65.

3. Cronin J, Crewther B. Training volume and strength andpower development. J Sci Med Sport 2004;7(2):144—55.

4. McGill SM, et al. Coordination of muscle activity to assurestability of the lumbar spine. J Electromyogr Kinesiol2003;13(4):353—9.

5. Luoto S, et al. Static back endurance and the risk of lowback pain. Clin Biomech 1995;10(6):323—4.

6. Biering—Sørensen F. Physical measurements as risk indica-tors for low-back trouble over a one-year period. Spine1984;9(2):106—19.

7. Koumantakis GA, Watson PJ, Oldham JA. Supplementationof general endurance exercise with stabilisation trainingversus general exercise only: physiological and functionaloutcomes of a randomised controlled trial of patients withrecurrent low back pain. Clin Biomech 2005;20(5):474—82.

8. Juker D, et al. Quantitative intramuscular myoelectricactivity of lumbar portions of psoas and the abdominalwall during a wide variety of tasks. Med Sci Sports Exerc1998;30(2):301—10.

9. Ito T, et al. Lumbar trunk muscle endurance testing: an inex-pensive alternative to a machine for evaluation. Arch PhysMed Rehabil 1996;77(1):75—9.

10. Moreland J, et al. Interrater reliability of six tests of trunk

muscle function and endurance. J Orthop Sports Phys Ther1997;26(4):200—8.

11. Essendrop M, et al. Measures of low back func-tion: a review of reproducibility studies. Clin Biomech2002;17(4):235—49.

T er d

runk muscle endurance tests: Reliability, and gend

12. Moreau CE, et al. Isometric back extension endurancetests: a review of the literature. J Manip Physiol Ther2001;24(2):110—22.

13. Suni JH, et al. Health-related fitness test battery foradults: aspects of reliability. Arch Phys Med Rehabil1996;77(4):399—405.

14. Latimer J, et al. The reliability and validity of theBiering—Sørensen test in asymptomatic subjects andsubjects reporting current or previous nonspecific lowback pain including commentary by Smidt GL. Spine1999;24(20):2085—90.

15. Evans K, et al. Predictors of low back pain in youngelite golfers: A preliminary study. Phys Ther Sport2005;6(3):122—30.

16. Leetun DT, et al. Core stability measures as risk factors forlower extremity injury in athletes. Med Sci Sports Exerc2004;36(6):926—34.

17. McGill S, et al. Previous history of LBP with work loss isrelated to lingering deficits in biomechanical, physiological,personal, psychosocial and motor control characteristics.Ergonomics 2003;46(7):731—46.

18. McGill SM, Childs A, Liebenson C. Endurance times for lowback stabilization exercises: clinical targets for testing and

training from a normal database. Arch Phys Med Rehabil1999;80(8):941—4.

19. Chen L-W, et al. Endurance times for trunk-stabilizationexercises in healthy women: comparing three kinds oftrunk—flexor exercises. J Sports Rehabil 2003;12:199—207.

Available online at www.

ifferences in athletes 455

20. Domholdt E. Physical therapy research: principles andapplications. 2nd ed. Philadelphia: Saunders; 2000.

21. Kenney WL, et al. ACSM’s guidelines for exercise test-ing and prescription. Baltimore: Williams and Wilkins;1995.

22. Shrout PE, Fleiss JL. Intraclass correlations: Uses inassessing rater reliability. Psychol Bull 1979;86(2):420—8.

23. Fleiss J. The design and analysis of clinical experiments.New York: Wiley; 1986.

24. Munro BH. Statistical methods for health care research. 3rded. Philadelphia: Lippincott; 1997.

25. Weir JP. Quantifying test—retest reliability using the intra-class correlation coefficient and the S.E.M. J Strength CondRes 2005;19(1):231—40.

26. Charter RA, Feldt LS. Meaning of reliability in termsof correct and incorrect clinical decisions: the art ofdecision making is still alive. J Clin Exp Neuropsychol2001;23(4):530—7.

27. Kankaanpaa M, et al. Age, sex, and body mass indexas determinants of back and hip extensor fatigue in theisometric Sørensen back endurance test. Arch Phys MedRehabil 1998;79(9):1069—75.

28. Mannion AF, et al. A new skin-surface device for mea-suring the curvature and global and segmental ranges ofmotion of the spine: reliability of measurements and com-parison with data reviewed from the literature. Eur SpineJ 2004;13(2):122—36.

sciencedirect.com