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De Blaiser C.1, De Ridder R.1, Willems T.1,2, Danneels L.1, Vanden Bossche L.3, Palmans T.1, Roosen P.1
1Ghent University, Department of Rehabilitation Sciences and Physiotherapy, Gent, Belgium, 2Ghent University, Department of Physical Therapy and Orthopedics, Gent, Belgium, 3Ghent University, Physical and Rehabilitation Medicine, Sportsmedicine, Gent, Belgium
Background: Numerous clinical tests have been suggested to help evaluate and identify deficiencies in core muscle performance. Isometric trunk holding tests, used to measure the endurance capacity of the core muscles are often applied. A frequent issue encountered in studies using such clinical screening measures is the insufficient validity and reliability of these tests. The reliability and especially validity of the commonly used prone bridging endurance test to measure localized abdominal muscle fatigue has not yet been investigated due to lack of a gold standard procedure. However, electromyographic (EMG) spectrum analysis has been extensively used to monitor the development of localized muscle fatigue, since fatigue causes a decrease of the median frequency content of the EMG signal.
Purpose: The aims of this study were to research the amplitude and median frequency slope characteristics of selected abdominal, back and hip muscles of healthy subjects during a prone bridging endurance test, based on surface electromyography (sEMG), (1) to determine if the prone bridging test is a valid field test to measure abdominal muscle fatigue, and (2) to evaluate if the current method of administrating the prone bridging test is reliable.
Methods: Thirty healthy subjects (15 ♂, 15 ♀) participated in this experiment. Electromyographic activity of seven abdominal, back and hip muscles was bilaterally measured to investigate validity. Amplitude and normalized median frequency slopes were computed from the EMG power spectra. A one-way analysis of variance with repeated measures design and post hoc pair-wise comparisons were made to compare the normalized median frequency slopes. Pearson correlation coefficients were calculated between the normalized median frequency slopes and the endurance time to evaluate their relationship. Finally, multiple backward linear regression analyses was performed to assess which normalized median frequency slopes best predicted the endurance time. For evaluating the reliability, the tests were performed on two separate days. Intraclass correlation coefficients (ICC) with 95% confidence intervals (CI) were used to assess reliability by utilizing a two-way random effects model with single measure reliability (ICC (2,1)).
Results: Significant differences in normalized median frequency slope values between several abdominal, back and hip muscles could be demonstrated. Moderate to high correlation coefficients were shown between normalized median frequency slopes and endurance time. Multiple backward linear regression revealed that the test endurance time could only be significantly predicted by the normalized median frequency slope of the rectus abdominis. Furthermore, statistical analysis showed excellent inter- and intra-tester reliability (ICC = 0.87-0.89).
Conclusion(s): This study is the first to support the validity and report an excellent reliability of the prone bridging test until failure for evaluating abdominal core muscle fatigue.
Implications: These results justify the use of this easy to administer, cost-effective test on a healthy population as a screening tool to detect abdominal core muscle endurance deficiencies and can be used in the fields of injury prevention, rehabilitation and athletic training.
Funding acknowledgements: No funding was used in this study.
Topic: Musculoskeletal
Ethics approval: This study was approved by the ethics committee of the University Hospital of Ghent.
All authors, affiliations and abstracts have been published as submitted.
