This seems to ring true, imo.
With the heart rate increase, fine and complex motor skills will initially increase in effectiveness, but only up to a point. And once that point is reached, they will deteriorate rapidly until they are lost to use.
For example the motor skills needed for Sight Shooting will improve until the heart rate reaches about 110 BPM, then they will rapidly deteriorate and be lost to use when the heart rate reaches about 130 BPM.
And as will be detailed below, the heart rate will at a minimum, go over 145 BPM in a real close quarters life and death situation.
As such, the fine motor skills that are needed for Sight Shooting will be lost to use.