MethodsParticipants between the ages of 18 and 40 years wereincluded in the study if they ran for 20 min or more at leasttwice per week. Sixty-six eligible recreational and competitiveendurance and sprint runners were recruited to participate inthe study through advertising at medical centres and fitnesscentres.
Participants were excluded if they
•Had a current severe injury, particularly acute or chronic low backpain.
•Were currently pregnant or had been pregnant in the last twoyears.
•Could not assume the correct leg positions involved in theSahrmann test.
•Had known cardiovascular disease, cancer, pre-/diabetes, coro-nary artery disease, moderate/severe angina, intermittentclaudication, moderate/severe dyspnoea or any other injury orillness which results in abnormal fatigue or muscle weakness.Informed consent was given by each participant preceding anytesting. This study was approved by the Human Research EthicsCommittee (Tasmania) Network (H0011312).Anthropometric measurements of height and weight wererecorded and body mass index (BMI) was calculated. Partici-pants performed a functional measure of anterior trunk musclestrength and then had diagnostic ultrasound image measurementsof the TrA taken. Participants then completed a questionnaireregarding frequency of ETAP symptoms. This was administeredlast to ensure blinding of the researcher collecting ultrasoundand strength information to the frequency of ETAP in theparticipants.The Sahrmann test is a functional graded exercise test used toassess the abdominal musculature, particularly TrA,10giving a scorefrom zero to five, with a higher score indicating stronger mus-cles. The Sahrmann test was described and demonstrated to theparticipants before practice attempt was performed. A stabiliserbiofeedback unit (Chatanooga group of Encore Medical, TX, USA)was placed in the natural lordotic curve of the lumbar region andthe participant instructed to perform the abdominal drawing-inmanoeuvre which consisted of the verbal cue from the investigator‘gently draw in your navel to your spine’. The biofeedback unit wasthen inflated to a pressure of 40 mmHg. Verbal cues for the cor-rect procedure of all five stages were given during the test. If thepressure on the biofeedback unit increased or decreased by morethan 10 mmHg at any time during the test the previous successfulmovement was recorded as their score. However, all five stages ofthe Sahrmann test were attempted and the test ceased after theparticipants had finished all movements or could not progress tothe next level. The participant was given a 2-min rest period inbetween trials to account for fatigue.A pilot study was initially conducted to assess the reliability ofultrasound measurements. Nine participants aged between 18 and50 had two repeated snapshot images of resting and contractedTrA conducted twice on the same day. The reliability of the operatortesting techniques was established through determination of intra-class correlation coefficient and typical error.Changes in TrA thickness during activation using ultrasound(GE LOGIQ BOOK, Jiangsu, China), were recorded with the lin-ear transducer transversely-orientated 3 cm medial to a line halfway between the 11th costal cartilage and the iliac crest.19Theparticipant was positioned in supine (crook lying) with armsbeside the body. TrA contraction was performed using the abdom-inal drawing-in manoeuvre. This manoeuvre has been shown tosignificantly increase the thickness of the TrA muscle.20Partic-ipants were given the opportunity to practice this manoeuvreprior to two ultrasound snapshots being taken immediately aftereach other with the participant in a relaxed position and thentwo snapshots during contraction of TrA. This procedure wasrepeated on the other side of the body. All images were takenat the end of normal inspiration, by the same investigator. Leftand right measurements (in cm) were summed and averaged forboth resting and contracted states, with thickness change cal-culated using the equation TrA thickness change = TrA thickness(contracted) – TrA thickness (resting). Contraction ratios were alsocalculated by dividing the contracted thickness by resting thick-ness. The reliability of these measures is reported in the resultssection.Participants then completed a questionnaire that recordedinformation regarding the severity (using a 10 cm visual analoguescale), frequency (recorded as incidence) and location of all ETAPexperiences using an A4 sized body map of the abdomen, delin-eated into 9 zones. Training volume for the total amount of physicalactivity performed (including running and other exercise sessions)was recorded as a weekly amount in hours and number of sessions.Four groups were established based on their rating of frequency ofETAP; weekly, monthly, yearly or never. The groups were coded 1for weekly incidence of ETAP, 2 for monthly, 3 for yearly and 4 fornever experiencing ETAP.Data is presented as mean and standard deviation. An analysisof variance (ANOVA) was used to compare the physical charac-teristics of the participants in the different frequency of ETAPgroups using STATA (STATA 12, College Texas). Chi-squared analy-sis was used to compare gender frequencies between the groups.Analysis of covariance (ANCOVA) using age and training as acovariates and Bonferroni post hoc test was completed to iden-tify between-group differences for muscle outcome variables (sizeand strength). Cohen’s d effect sizes were calculated on the differ-ences between groups when significant differences were identified.The relative impact of the variables of strength, age and train-ing on the outcome of ETAP frequency were assessed using mixedmethod Poisson regression to determine incident rate ratios (IRR)on z score values of the relevant variables. Pairwise correlationbetween the Sahrmann test and TrA thickness change was per-formed. The minimum significant difference was determined bya p value <0.05.Based on the dependent variable of TrA thickness from previousresearch,21detection of a difference in muscle thickness changeof 0.08 cm between the groups would require group sizes of 13 pergroup to provide a power of 0.8. Hence 66 participants were initiallyrecruited to account for potential attrition.
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