Intensity, Muscle Size and Power
In the Olympics, which track athletes have the largest muscles?
Is it marathoners, who train by running up to 60 miles per week, then engage in an event that lasts about 2 to 3 hours?
Or is it sprinters, whose entire run lasts for about 10 seconds?
Compare a shot putter to a baseball pitcher? Who puts in more time? Who has the larger muscles?
The biological reason is that efforts that require a great amount of power require large muscles, whereas efforts that require a long effort only require a good blood supply and efficient energy system for a small muscle.
But here is the interesting point. In the sprinters, and in the shot putter's, even though their effort is all out, they are not exhausting the intermediate twitch, or the slow twitch fibers. And yet still their muscles grow larger then even the people who only exert slightly less power over only slightly longer times periods (400 meter people, javelin and discuss throwers)
If it took long duration efforts to produce muscle, or if duration (the extra time spent) helped build muscle, even a little, then the musculature distinctions between each higher distance, lower speed event would not be so clear.
At almost every increase in distance, and in time to the event, the average muscles size goes down.