Why a Soft Left Arm is Better (by Tom Patri, Golf Illustrated, 1995)

Rethinking one of golf’s oldest swing instruction ideas — the “stiff’ left arm (Part 1)

Keep your left arm straight! That is one of the oldest and most misinterpreted commands in all of golf swing instruction. Most golfers, ever anxious to not lose control of the club, accept the dictum without question. Anything less than a straight left arm would seem too loose. Won’t the club wobble during the swing? How can you generate enough power without a ram-rod arm doing the work, the way a machine stamps out steel plate? The result of this misguided thinking is tension. Thus, the stiff left arm produces the opposite of what it’s supposed to yield. The swing of both arms is, or should be, a momentum. Momentum is to say, speed. Speed (plus the mass of the clubhead) develops power. Muscular tension impedes speed.

Perhaps the misinterpretation derives not only from verbal instruction, but from what the game’s best players appear to do. It looks like their left arm is straight. But, in fact, there is a certain give that may not be discernible to the naked or untrained eye. There are, by my reckoning, 11 key joints in your golf body — the joint in your neck that allows your head to swivel, the rotator cuffs, elbows, wrists, knees and ankle joints. Six of the 11 joints are in your arms, which is why I’m concerned with arm-swing tension.
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Fred Couples is a well-known proponent of the soft left arm swing. Note the bent left arm at the
top of his backswing (left), and that it has straightened at impact, when it counts the most (right).

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The left arm represents half of the total arm swing, and relative to the right arm will have a straighter attitude. But if it’s rigid, you’re giving up nearly 50 percent of the power you would otherwise get from your arms. If I can convince you that the left arm should not be rigid, that a “soft” left arm is the way to play, you will have at impact all the power possible. How to do it?
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To achieve a “soft” left arm:
The swing is initiated not by the hands or arms, but by the upper back muscles. This move is reflected by the “lag” take away (Fig. 1), in which the clubhead is effectively the last to leave the ball. The hands seem to be pulling the club back, although that is not actually the case.