A question for the uber well versed in biomechanics:
How does the hand grip type (thumbs included, no thumbs, four fingers, three fingers, two fingers, one finger) effect the muscles used in a pullup?
Dropping from four fingers to three appears to make a massive difference in the amount of power (wattage) of the pull up. I’ve measured this by determining heart rate differences between the two type. Converting from heart rate to power is a bit of a black magic art, but any conversion trick used does not seem to account for the increased work load. My guess is that the biomechanics of the pullup are more different than just the activation of some of the for arm muscles dependent on the hand grip position.
Are you talking about grip from the standpoint of how your hand holds the bar, with width unchanged, or are you talking about varying the width of the hands?
I would assume that the width remains the same and that all prehensions are pronated (palms facing away), otherwise too many variables enter the equation.
I’m no biomechanics expert, but I’ve done a fair amount of pull ups over the years, with many different prehensions, and at first I’d say that the biggest role is played by how strong the chosen prehension is, relatively to the “normal” one (four fingers and thumb). I think that when working with weaker prehensions, it’s more difficult to apply the force, with most muscles involved remaining the same and some minor changes in the muscles of the forearm.
Also, the relative lengths of the fingers play a big role when working with three or two fingers.
Removing fingers on a pull-up just creates a weak link with your grip. It would do the same for a deadlift.