Muscles don't shorten their filaments — they slide them past each other. Myosin heads grab actin and ratchet it inward, pulling the Z-lines together. The filaments stay the same length; the sarcomere gets shorter. Watch it.
The sarcomere
Sliding filamentrelaxed
💡 During contraction the A-band stays the same width (it's the length of myosin), but the I-band and H-zone shrink as actin slides in. That's the giveaway on an exam.
📷 Reference image
A real labeled figure to compare with the interactive above.
Sliding Filament Contraction — OpenStax, CC BY 4.0 (via Wikimedia Commons)
