Roger N wrote:
A close grip gives you faster and slightly more powerful strikes...
Roger N wrote:
A wide grip gives you... slower and slightly weaker strike
You got the engineer in me thinking with these ones Roger; and I don't its as simple as that.
A single sword cut uses a whole chain of muscle movements involving wrists, forearms and shoulders both on the left and right arm (I'm intentionally leaving out hip or other body force generation for the moment). And these muscle groups are really important because they will define speed & impact strength specially at 2 very important moments in any attack:
a) The start of the attack (where the sword starts moving from say, a guard)
b) The onset or 'ending' of an attack (where the moving sword is about to strike or cut its target)
The start of the attack is where your sword starts its movement from its starting point (a guard like pflug or vomtag). To do that, you use the "big muscles" (a quick, linear, sniping shot from vomtag would only use forearms; a powerful, circular cut from pflug would start with the shoulders)
and its my experience that a wider grip helps to accelerate the sword at this stage easier than with a short grip, precisely because of the "rotational point" the wider grip gives you, keeps the sword at a fixed angle from your lever (in this case your arm) and the tip isn't left behind in the attack, making your movement more efficient.
Now at the onset of the attack is where the physics get complicated (because your attack comes in a complex curve, and at high speeds some materials start to bend; also at this point the force generated by hip and other body parts must be taken in consideration in total strike "speed" and impact).
But its at this stage that the wrists shine because of the important job they do (the wringing motion as if with a towel, Magnus & Andrew mentioned). And yes, a close grip with both hands tight together would get your (already-moving) sword accelerate even more than keeping the wide grip you started with.
Trying to sum it up, I guess the mechanics of chopping wood with a long-hafted axe would illustrate what I see.
You raise the axe (to vomtag!) effortlessly with a very wide grip, and bring it down quickly with a close grip. In jargon:
Translational acceleration (where the sword always faces your body the same way even though the tip changes angle) is accomplished easier (with less effort spent) with a wide grip.
Rotational acceleration (where the sword changes angle AND face regarding your body) is easier with a close grip.
Which grip is best for speed and impact strength, will depend on the kind & angle of attack you wish to make (and also if you think you'll need to parry or attack again in a hurry).
Sorry for the mess!