Igor Andreev Apr 20, 2018:

The fact that general training means and methods addressing strength and power will improve speed is linked to the trainability of speed versus endurance. In fact, endurance is much more trainable than speed, which is more genetically set.
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For instance, trainability determines that endurance training for long-duration sport should be based mainly on specifi work, which can represent up to 90 percent of the annual training time. By contrast, the more limited speed trainability requires major focus on general elements (such as strength and its various expressions).
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This training philosophy takes to the extreme the fundamental physiological principle that a given type of work results in a specific adaptation, but contradicts the methodological principle that specifi adaptations are
maximized on the base of general adaptations, especially for low-trainability biomotor abilities such as speed.
Periodization Training for Sports by Tudor Bompa and Carlo Buzzichelli, 2014