Question: do dolphins have muscles that are made up from stronger cells, so they can swim effectively?

Valeria Senigaglia answered on 18 Jun 2012:

No dolphins muscles are very similar to ours. They effectively swim because they have more muscles, they are more train than us, they have slim and hydrodynamic bodies (made so that they “drag” less water and so their bodies encounter less resistance from the water and they can go faster).

They also have some additional proteins called mioglobins that allow them to store oxygen in the muscles but this helps them to hold their breath for longer not to swim faster.

Moreover their propulsion (moving their tail up and down) is very effective.