imagine that.... core endurance can affect running performance.
Let us see ...as you start to fatigue, you have a tendency to bend forward more at the waist. This is probably due to not only decreased quadriceps/hamstrings ratios but also decreased abdominal/lower back extensor endurance ratios. Of course, we could say that asyou fatigue, you become more quadriceps dominant and less gluteal dominant, which would also be correct.
Ankle eversion also increases as you fatigue. No surprise here. Think about the action of your gastroc/soleus group as the medial gastroc acts to invert the ankle and help promote supination, particularly after mid stance. Also think about all the posterior compartment musculature of the lower leg which contract eccentrically during the first phase of gait to assist in deceleration of pronation. From about mid stance on, the extensors should activate, along with the foot intrinsics to assist in providing a stable base. As we fatigue, this mechanism too appears to begin to fail.
Moral of the story? Keep your core in shape and do lots of endurance work!