Anterior and posterior rectus abdominis sheath stiffness in relation to diastasis recti: Abdominal wall training or not?

Introduction: This study explores the anatomical relation of the rectus abdominis muscles with the anterior and posterior rectus sheaths. The elastic behavior of these fascial sheets is also assessed. Both of these analyses form an anatomic-biomechanical basis for diagnosis and treatment, especially in relation to diastasis recti abdominis (DRA). Method: Fundamental observational, biomechanical study. Seven post-mortem, embalmed human specimens were dissected. The abdominal muscles and the fascial sheets of the abdominal wall were dissected. 4 x 4 cm samples of the anterior and posterior rectus sheaths were loaded in longitudinal and transverse direction, while recording elongation by means of a displacement sensor. The main outcome measures were anatomical descriptions and elongation of fascia samples in mm (mean and standard +/- deviation). Results: In longitudinal direction the posterior rectus sheath samples stretched over 1.67 +/- 0.48 mm, while in transverse direction the mean stretch was 0.29 +/- 0.18 mm (p = 0.001). In contrast, no significant difference between longitudinal (0.78 +/- 0.43 mm) and transversal displacement (0.50 +/- 0.23 mm) was observed in the anterior rectus sheath (p = 0.56). Discussion and conclusion: The posterior rectus sheath is functionally more related to the transverse abdominis muscle than to the rectus abdominis muscle. From this connection, in combination with the specific stiffness of the posterior fascia in the lateral direction, it is assumed that the transverse abdominis muscles play an important role in the etiology but also in reduction of DRA. The transverse abdominis and rectus abdominis muscles collaborate in support of the abdominal wall. (C) 2019 Elsevier Ltd. All rights reserved.