The effect of size, sex and running discipline on the shape of rectus abdominis muscle: A 3D geometric morphometric approach.

Sex had a significant effect on the 3D shape of the rectus abdominis muscle at rest.

• Males showed a more triangularly shaped rectus abdominis, wider in its superior part.
• Females showed a more rectangular muscle.
• Shape was assessed with 3D geometric morphometrics on in vivo models built from CT scan slices.

Running discipline had a significant effect on rectus abdominis 3D shape.

• Sprinters showed thicker and more rectangular muscles than endurance runners.
• The sample consisted of athletes specialised in endurance running or sprinting.
• This matches the hypothesis that the explosive demands of sprinting require a more specialised morphology.

The study modelled the in vivo 3D shape of the rectus abdominis from CT scans, a muscle whose 3D morphology is poorly documented in living people.

• The muscles were measured directly from CT scan slices.
• 3D geometrical models were created by triangulating 3D coordinates.
• The design was observational and cross-sectional, with muscle shape analysed at rest.

The study tested for allometric (size-related), sexual dimorphism and running-discipline effects on muscle shape.

• The hypotheses were that allometric effects, sexual dimorphism and a more specialised sprinter morphology would be present.
• The abstract reports significant effects of sex and running discipline; it does not state a size effect as a main finding.

The authors suggest the functional anatomy of the rectus abdominis may differ by sex and running discipline, with possible implications for biomechanics and respiratory performance.

• The muscle is closely related to trunk stabilization and breathing.
• The authors state the approach could be applied in sports science and in clinical settings.