What is Scalpel technique in Guitar ?
I searched on internet but does not show proper results.It says
"Scalpel - move only your thumb and forefinger"
Can you please guide me through videos,images that can be helpful.
After watching the video in the linked thread from the comment, this last guess is closer to the mark. It's a tremolo technique apparently. As PD in the first video comments, being rigid will lead to fatigue. And allowing more muscles to help will distribute the effort. From a Hatha Yoga perspective, even your left big toe should be doing it's part to help: gripping the floor ever so slightly to counterbalance the other muscular forces.
This video appears to lay-out the exact differences among the different tremolo styles. Scalpel apparently involves just the thumb and forefinger, as you had already gathered, with the hand anchored but not rigid.
There are a number of conflicting physical phenomena that make it difficult to find a comfortable balance. For a nice tremolo picking, you want an even, sustained sound.
If you choke-up on the pick and allow only sharp tip of the point to attack the string, the friction will be low and less energy will be lost into the strings. Less friction means less sound, less oscillatory power is being transferred to the strings. Also, again since little energy is transferred, it will require some musculatory action to stop and turn around.
If you allow more of the pick to attack the string, you may find a sweet-spot where the energy lost from the movement of the hand is exactly what your hand needs to do the stopping. Then you can factor-out that muscle action. Your fingers and wrist don't need to expend energy on the slow-down turn-around. As a baseball analogy, you don't try to land on home plate, you aim for a spot past the plate so you don't throw away your speed, you pass the plate at full-tilt. I suppose the analogy doesn't really hold because our poor ballplayer is obliged to trip over the plate every time.
Ehrm. Does that make any sense?
The video also talks about changing the angle of the pick so there's more edge. This gives a scraping, shimmering effect somewhat evocative of a Sitar which uses a wire plectrum striking the string edge-on. That's friction. It pulls energy out of the motion, so adding this effect will require more expenditure from the muscles to compensate.