It's odd that it's very easy to stumble across sets of rules that generate this same basic figure.

Name: muscles2
Description: "More Muscles"
Definitions:
{
D -> F
}
Angle: 90.0
AngleIncrement: 1.0
Width: 2.0
WidthIncrement: 1.0
Length: 1.0
LengthScale: 1.1
Axiom: D
Rules:
{
D -> DD+
}