Difference in lateral abdominal muscle thickness during forceful exhalation in healthy smokers and non-smokers.

Abstract

The present study aims to determine whether the internal oblique (IO) and transversus abdominis (TrA) muscles, which are major lumbar stabilisers and also expiratory muscles, are affected by smoking. A total of 31 healthy individuals in their 20s (smokers: 15; non-smokers: 16) voluntarily participated in the study. They were made to maintain an upright standing posture with their scapulars on the wall. Then measurement was taken on the thickness of their right IO and TrA while they were at rest and in a state of forced expiration using a 7.5 MHz linear probe, an ultrasonic imaging system. The thickness of the muscles was converted into the percentage of change in muscle thickness (PCMT) and relative contribution ratio (RCR) using a calculation formula, and then the data were analysed. Significant differences were found between the two groups in the PCMT of the TrA and in the RCR of both TrA and IO. Smokers have a relatively higher degree of dependence on IO than TrA during forceful expiratory conditions compared with non-smokers. This relative overreaction of the IO is considered to likely cause problems in efficiently diffusing loads of the spine.