Banging out more reps on a machine after barbell fatigue is a no brainer, you can lift more on the machine it self.
So go from the barbell to a lighter weight and you’ve got the same result.
Does more muscle recruitment=greater CNS stress? If so again no brainer between the machine and barbell.
But attributing the CNS stress is relative. Would the machine result in the same magnitude of CNS stress(CNS energy to # of recruitment) ? Would the extra overall CNS stress from barbell to machine weights really affect sprinting that much? Is your goal in the weight room to do as little CNS stress as possible?
I put question marks because I don’t know the answer.