Effects of mouthpiece shape and expiratory threshold loading on contraction of the lateral abdominal muscles: A cross-sectional study

Abstract

BackgroundExpiratory tasks may facilitate transversus abdominis (TrA) activity for spinal stabilization. The purpose of this study was to verify whether a combination of pursed-lip breathing (PLB) and use of an expiratory threshold loading (ETL) device to increase expiratory resistance would promote TrA contraction comparable to that for a stabilization exercise. MethodsTwenty healthy men performed expiratory tasks or an abdominal drawing-in maneuver (ADIM). Expiratory tasks comprised combinations of ETL settings with 0%, 5%, or 15% of maximum expiratory pressure, and mouthpieces with a normal shape or pursed-lip shape. B-mode ultrasound imaging of the TrA, internal oblique, and external oblique muscles was performed to determine percentage changes in muscle thickness. Percentage changes among tasks were statistically compared for each muscle. FindingsTrA thickness increased with normal lips at 15% ETL, with PLB with 5% ETL, and with ADIM (p < 0.01 each). Internal oblique thickness increased under all PLB conditions (p < 0.01 each). No significant differences in external oblique thickness were seen for any tasks. The total thickness of the lateral abdominal muscles was significantly increased not only for 15% ETL tasks and ADIM, but also for PLB with 5% ETL (p < 0.02 each). InterpretationThese results indicated that PLB with 5% ETL could facilitate the same level of TrA activity as the ADIM. PLB with 5% ETL was the only task that simultaneously increased overall lateral abdominal muscles, including the internal obliques, and might be readily applicable in clinical situations.