a car basically needs two things to run: an engine and a chassis. The human body works very similarly.
in order for a car to put the performance of its engine as efficiently as possible onto the pavement, you need to tighten up the chassis in the right spots. Again, the human body works very similarly.
translated into the human body: in order for the heart to put its performance as best and as efficiently as possible onto the road, the core muscles attached to the pelvis need to be comprehensively trained by a specific core strength- and conditioning program.
no need to overdo it, though. the more muscles you have, the more weight you carry around.
An improved core strength will help you to perform and execute better technique especially in the latter stages of a race, where you need to rely on more than just endurance output.