Fortunately a muscle is nothing like a hose, it works on the same principle as a solonoid, an electric magnet. When a current is present the magnet pulls a pin further into the recepticle. The formula one motors operate the valves this way and up to 17,000 rpm. The Japanese have the superfast trains pulled by magnets.
If one keeps pulling the pins out the magnet speed slows down. If you want more speed put another solonoid in. Fast twitch/slow twitch, remember short fibres/long fibres. When the kid is growing the bones lengthen at the growth plates and the muscles stretch as do tendons. Make more solonoids, remember the short solonoids are fast.
Does stretching as an exercise lengthen the fibres or promote the growth of more short fibres.
The African gene has short calf and long tendons.