Nisus is a noun that refers to a mental or physical effort to attain an end.
Nisus comes directly from the Latin (NEEZ zoos) where its pronunciation may differ a little from its English descendant, but its meaning has remained roughly the same. A nisus is an effort, but more specifically, it one to reach a particular goal.
No matter what nisus he employed, Larry simply couldn’t finish the race. It bothered him to fall short of his goal in spite of his best efforts.