The same is true of runners. Compare them with body builders or football players (to use and extereme example). "Arnold" needs to move a massive amount of weight at one time. It requires larger bundles of muscle fibre. while the long distance runner only needs to repeat the same efficient motion 1 million times. This requires thinner muscles.
I did the Face of America Tour a few years ago to commemorate the 911 victims. There were lots of police and fire fighters on the ride from New York to Virginia. The "big burly" guys, while generally fit, had a hard time with distance and speed, while the lightweights cyclists spun along at a nice pace. It's a mater of musclel type.
This is of course a generalization. There are many exceptions to the rule.