[Mike O]

It's the lever assemblies - which include the hands, the clubhead, the shaft, the left arm which if start down to fast, you as a person just can't maintain that rate of acceleration past impact, and at the point you cease to accelerate you will experience throwaway. But the place that you monitor or sense how much acceleration you have and whether you will have or do have throwaway is the hands. So back to your question hands or clubhead?- the answer would be hands i.e. "the hands are initally over accelerating based on the length of downswing distance they must cover and the maximum speed that you can move them and your solution would be to reduce the acceleration or shorten the stroke.
Mike O. (Make sure you follow his cross references here for more insight)