This kind of exercise is comparible to the kind of flexibility training performed by martial artists and gymnasts. Its called active static and active dynamic flexibility. This is just like a martial artist having the ability to perform a high kick, or to hold the leg in the air for extended periods of time. Its requires both flexibility of some muscles (those that tense and resist the motion) and strength in others (those that have to power the motion). Im no expert of this, but have read up on the subject.
In the case of the hand, and playing wide chords, there seems to be several criteria:
- Ability to reach maximum stretch in a short period of time (ie, the time it takes to hit a chord)
- Ability to hold this position for the required duration with no assistence from outside forces
- Ability to remain relaxed
All of these criteria would benefit from the right strength and flexibility training imo. The only question remains, whether it is safe to perform such exercises on the hand? This Im not sure. If ligaments are being stretched rather than muscles, then it will result in major problems (as Schubert discovered!).
However, such problems usually arise from isometric exercises, and this is not what we're talking about. I believe that relaxed static stretches combined with dynamic exercises would help a great deal.
Ofcourse, one has to be realistic. If a chord is out of reach, then it is out of reach! In this case, it might be more wise to spend this time developing the ability to arpegiate the chord instead.
As far as tw0k1ngs is concerned, Im really not sure what to recommend. Maybe practicing single hand scales in 11ths and 12ths, while trying to keep the hand relaxed (and stopping as soon as tension sets in). Maybe playing a hard chord and holding it until the muscles completely relax. Things like this are the safest and should help.
Id be interested to know whether you can form a 180 split between 1-5? If so, then its really the opposing muscles that need to be trained so that they are strong enough to reach this range of motion quickly and effortlessly.
SJ