Ordinarily in designing tools for human use -- the science of "ergonomics" -- the USE motion is fitted to the HUMAN movements and shapes of body parts so the FORM of the tool as used by the human form and motion optimizes efficiency, effectiveness, and human strain.
In golf, the RULES of golf somewhat interfere with this basic approach, but golf grip makers DON'T USE ERGONOMICS ANYWAY, so that hasn't mattered. Grip makers have been making full-swing grips "okay" and then simply sticking a full swing grip on a putter for over a hundred years.
The only ergonomic design features have been "tackiness", "sponginess", "flat top handles", and "pistol grips" in which a rear bulging forms into the finger cradle of the human hand. Dilettante grip designers have done "two thumbs" wide grips and "fat grips" and angled grips for directing the hand motion.
The way grips "taper" to thinner at the bottom is not a real choice for design and is mostly a holdover from history and habit. Tapering makes too-thin grips AND mid-size grips bad design UNLESS the middle section of the grip is actually where the golfer's hands naturally present themselves in space. To KNOW THAT requires a) knowing good putting form and why it is that way, and b) studying standard human body sizes and shapes and angles. Putter makers and grip makers don't have either a) or b) going on. If a putter is too long for where the good-setup golfer's hands present, the golfer is forced to choose between gripping the handle too low and in the tapered too-thin area or lifting the hands higher to grip the middle of the handle where the grip diameter is at least not worse for thinness.
The pistol grip is now illegal. Of all the ergonomic designs, the only three that make much sense are flat-top handle and mid-size grips and tackiness.
The ultimate objective is not to SENSITIZE the nerves of the fingers and palm skin but to settle the hands out so they are largely PARKED and KEPT STEADY and FORGOTTEN ABOUT.
If a grip calls attention to the hands, that grip sucks. So the FAT grips are the worst of the lot.
A grip that is too thin to fill the normal human hand when the fingertips fold to the butt of the palm or nearly so has been the standard offering for decades from the likes of Golf Pride and all the rest of the usual suspects. Mid-size grips haven't really been used much except for the past ten years or so. So what's up with that?
A full swing handle fits along the fingers, not aligned in the lifeline of the palm. So the gap between the fingertips and the butt of the palm for the full swing is more open than it is for putting, especially in the lead hand and the little finger's fingertip. But in putting, the handle should align more in the palm along the lifeline with the fingertips closing the gap a bit more. If you do this with a regular full-swing grip with too-thin diameter, it makes your hand "clutch" the handle. But a MID-SIZE grip better conforms to the usual size of adult golfer hands (at least for males), and the golfer can align the mid-size grip in the palm and HOLD it steadily without a sense of "clutching" it. The fact that the mid-size make ample contact with the underneath cradling fingers is a big plus in grip function. Getting rid of the little "air pocket" between the little finger and the underside of the grip eliminates an annoying potential source of management problem, so again the mid-size is a plus.
The Rules either specifically forbid certain design choices or implicitly discourage weirdness, and I'm fine with that -- traditional golf without weird equipment and techniques is more important and valuable that some golfer getting a marginal benefit in his personal game from wacky and weird equipment and technique.
Going forward, there is no evidence that today's MID-SIZE grips are actually formed in light of human hand shapes -- the science of "anthropometry" or knowing patterns of human forms for sizes and shapes of the body and body parts. Grip makers simply are filling a gap that the market is demanding, having seen some pros wrapping their too-thin grips with gauze or tape to fatten them up a bit -- but the manufacturers still haven't started studying standard human hand forms to decide exactly what diameter the grips should have.
AND the putter manufacturers show NO EVIDENCE of ever having looked at human form of the arms as they naturally hang at address before the putter makers decide the LIE ANGLE they design and sell. The human forearm hangs off the upper arm not vertically but at a "dangle" out of vertical of about 14-16 degrees. So a lie angle of a putter that presents the shaft axis to match the forearm axis of the natural arm hang would have the shaft lean back from vertical the SAME 14-16 degrees. That would be a lie angle in the stupidly reversed golfspeak of 90-14= 76 degrees "upright", compared to standard off-the-shelf offerings of 71 degrees or 19 leaning back from vertical.
And the way the HAND naturally hangs off the end of the forearm is vertical, so the angle from forearm to hand axis is the SAME 14-16 degrees as the forearm angle to the upper arm axis. That's why aligning the handle and grip along the lifeline matches the axis of the shaft to the axis of the forearm -- the lifeline ANGLE across the palm meets the axis of the forearm in the SAME 14-16 degrees and when the hand HANGS off the forearm naturally, the lifeline drops rotationally into alignment with the forearm axis.
If you hold your hand up to your face palm-towards-you and hand extending straight off the forearm the lifeline makes an angle off the forearm axis of about 14-16 degrees, But if you cock the hand thumb inward toward the middle of the body, the lifeline aligns with the forearm axis. That is the angle the hand naturally hangs off the forearm in a resting state. The LIFELINE is the crease gravity makes by folding the butt of the thumb pad into the palm like a pillow draped on a bannister. The LIFELINE then is MADE so that a naturally-hanging hand conforms with the forearm axis of the naturally hanging forearm.
What's GOOD about these natural angles is 1) they are natural and don't require the golfer to do anything weird, and 2) they are set by gravity not the golfer so getting them is free, and 3) moving the arms is STRAIGHTER and less trouble when the arms are hanging in equilibrium with gravity as opposed to being held out away or tucked up high in OPPOSITION to gravity. Opposing gravity introduces torque forces that bother the stroke and require more muscle tension to control, whereas in contrast swinging arms in gravity equilibrium "channels" the stroke with LESS torque so straighter with less muscle control is much more likely. Variations in muscle tone plus a torque waiting to pounce is always a dumb idea. So bad angles in putter design makes for unnecessary torques.
And also in general, making the tool of the putter an EXTENSION of the forearm affords better incorporation of the tool into the brian processes for aiming and moving the putter accurately with good precision in line and distance control, more like an adopted part of the body and less like a mechanical add-on.
So there is a SECOND problem for grips -- undefined good thickness is the first, but bad too-flat lie angles are a second problem.
When the lie angle is too flat, the golfer has to make a choice: 1) either hold the shaft into the natural forearm angle with the result that the putter head is closer to the feet than designed for and the heel is up off the ground and the sole of the putter not flat to the surface, or 2) deal with the handle NOT fitting into the palm and along the lifeline and allowing the too-flat lie to meet his naturally hanging hand so the handle fits into the fingers, not the lifeline. A potential THIRD choice is to re-aim the hanging hand onto the too-flat handle to get the handle into the lifeline, but this is pointless unless the handle actually matches the FOREARM axis, and doing this with the wrist loosens the hand on the handle and makes the shaping of the thumbs and fingers "indefinite" compared to so-called "high hands" arched into the natural hanging angle off the forearms.
I like the natural hand-hang angle and not a deliberate poking down of the hand off the forearm or a deliberate arching down of the hand off the forearm. A natural hand hang plus modest grip and muscle tone shapes the hand quite nicely and athletically, and sets the hands in a natural way and without calling attention to the hands during the stroke.
But if the putter lie is too-flat -- which is ALWAYS true since putter manufacturers are NEVER attentive to human form and good putting postures and movements -- I prefer the FLAT SOLE and so opt for choice 2 above -- just deal with the bad design of the putter making the handle sub-optimal for gripping. This leaves the stroke flat thru impact to roll the ball on an axis of roll that always is perpendicular to whatever surface tilt the ball starts on, without the manipulations required to swing a heel-up putter down the line to start the ball exactly where the putter face aims at address.
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