In regard to the cyclists this observation has , at least in one review, been used to bolster the argument that "too much exercise" is harmful , i.e. support for the "U-Shaped" curve theory."Too much " exercise certainty can be harmful (maybe that is what "too much" means) but reduced resting EF in elite athletes is not proof of that contention.
The "wisdom of the body "may dictate that maintenance of stroke volume a priority and not EF. These athlete have large preloads ( aka end diastolic volumes) so that a smaller percentage can be ejected to maintain the resting stroke volume. These basketball players had a normal increase in stroke volume and EF with exercise as did the NFL players.I believe the exercise EF was not measured in the cyclists.
1.Abergel, E. Serial left ventricular adaptations in world -class professional cyclists.J AM Coll Cardiology July 2004.