Source: The Great Interpretation of Dreams (Ibn Sirin)
Muscles in a dream indicate strength and power. Their strength indicates the man's strength, and their weakness indicates his weakness.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
Muscles indicate the family and tribe by whom a man is strengthened.
Source: Signs in the Science of Expressions (Ibn Shaheen)
Muscles are interpreted as wealth. Whoever sees his muscles are strong, his wealth will increase.