The transversus abdominis (TrA) is a core muscle that contributes to functional mobility and lumbar stability. This study aimed to compare the changes in TrA thickness during different Pilates exercises, and to identify the exercise that elicited the greatest TrA activation. Forty-four healthy women were divided into two groups: young (25–35 years old) and middle-aged (36–55 years old). TrA thickness was assessed by ultrasound while the participants performed five Pilates exercises: basic position, hundred, hip roll, side plank, and dead bug. A repeated measures analysis of variance revealed that the dead bug exercise induced a significantly higher increase in TrA thickness (relative to rest) than the other exercises (p < 0.05). The young group also showed a significantly higher overall TrA thickness than the middle-aged group (p < 0.05). The findings suggest that the dead bug exercise is the most effective for enhancing TrA activation among the Pilates exercises tested. The basic position and the hundred exercises can be used as warm-up exercises before performing more challenging exercises such as the hip roll, the side plank, and the dead bug. The sequence of exercises can be similar for both young and middle-aged women.

Purpose Strength of the core muscles and the transversus abdominis (TrA) play an important role in the functional mobility and lumbar stability. Quantification of TrA thickness using ultrasound is used as an indirect index of muscle recruitment. The aim of this study was to determine if, and to what extent the thickness of TrA is affected in different Pilates training positions, and which position causes the greater increase in TrA thickness. Methods Forty-four healthy women were divided into a young (25 - 35 years old) and middle-aged (age 36 - 55 years old) group. TrA thickness was quantified using ultrasound whilst the participants performed the basic position, the hundred, bridge, side plank and the dead bug exercise. Results Analysis of variance showed that dead bug exercise showed greater TrA thickness (relative to rest) than the remainder exercises (p < 0.05) while the younger group had greater overall TrA thickness than the middle-aged group (p < 0.05). Conclusions Based on these results, it is concluded that the most preferable exercise for greater TrA thickness increase is the dead bug exercise. Pilates exercises such as the basic position and the hundred exercises, can precede the exercises that present a larger TrA thickness, such as the bridge, the side plank and the dead bug. The order of exercises can be similar for both young and middle-aged women.