For a right handed golfer the “trail arm” is the right arm and the “lead arm” is the left, however this definition like other terminology in golf can be a little misleading. It can easily be interpreted that the lead arm is the important one and has all the control, this just isn’t the case. For sure some people will at times need to focus on specific parts of the body like the “lead arm” to achieve certain movements they are working on. A common focus for lot of golfers at some point has been on keeping the “lead arm” straighter in the back-swing.
If you were to take a look at golf swings from the viewpoint of “Ideal” then there is certainly some characteristics that often appear in the “trail arm” of these swings (usually tour golfers or plus handicap amateurs) that are different a good number of club and social golfers. I have highlighted the typical differences below at various stages in the swing.
The ideal swing will have a slight bend (about 10 degrees) in the “trail arm” at address whereas the club golfer may have a tendency to be too straight. Another point is that elbow is pointed more towards the hip joint (supinated arm or turned out slightly).
Half way back
The club golfer will tend to bend the trail too much too early so at this point the will have up to twice as much bend as the ideal. This immediately loses width and what can often be described as a “connection” between arms and torso movement.
Top of back-swing
Once again the ideal is bent a lot less than the club golfer. The ideal may have somewhere on average between 75 and 90 degrees, the club golfer being over 120 + degrees. This can often be a symptom of poor mid back mobility or/and poor scapula (shoulder blade) stability. Another point is the ideal “trail arm is more externally rotated.
Half way down
Same characteristics here with the ideal having less bend than the club golfer. Another difference will be that the wrists will have unhinged more (casted) in the club golfer whilst the ideal will still retain this leverage.
Here is where the trend reverses slightly with the club golfer having a slightly straighter “trail arm” than the ideal. This is due to the less leverage (lag) in the wrist area so the “trail arm” has compensated.
These are of course general observations of the two different standards of golf swings. The overall message is not to just think of what the “lead arm” is doing in your swing but how the “trail arm” can be an efficient piece of your golf swing puzzle.